リョウブとコバノズイナ（姫リョウブ）はいずれも「リョウブ」と呼ばれることがある種類で、植栽されることのある落葉樹です。本来分類的には全く異なる種類ですが、花のつけ方や葉や果実の性質などが似ており、混同されてコバノズイナを「リョウブ」と呼んでしまう事例もあります。2種を区別するには葉・花・果実をきちんと確認する必要がありますが、知っていれば比較的区別は容易です。本記事ではリョウブとコバノズイナ（姫リョウブ）の分類・形態について解説していきます。

リョウブ・コバノズイナ（姫リョウブ）とは？

リョウブ（令法） Clethra barbinervis は日本の北海道（南部）・本州・四国・九州；朝鮮（済州島）に分布し、山地の岩場や乾いた斜面などに生え、公園などに植栽されることが多い落葉小高木です（神奈川県植物誌調査会，2018）。春に枝の先にかたまってつく若芽は山菜になり食用します。

コバノズイナ（小葉の瑞菜） Itea virginica は別名アメリカズイナ、姫リョウブ。アメリカ合衆国南東部原産で、日本では園芸で利用され、観賞用や生け花用に庭木や鉢植えとして栽培される落葉低木です。

いずれも「リョウブ」と呼ばれることがある種類で、総状花序を出し、白い小さな花を多数つける点や、葉に鋸歯がある点、果実が蒴果（乾燥しており裂開して種子を落とす果実）などはかなり似ています。

生け花ではコバノズイナを、「姫リョウブ」または単に「リョウブ」と呼ぶことがあり、大きな混乱を招いています。

リョウブとコバノズイナ（姫リョウブ）の違いは？

しかし、まず分類が大きく異なっています（茂木ら，2003；神奈川県植物誌調査会，2018）。

リョウブはリョウブ科リョウブ属に含まれるのに対して、コバノズイナはズイナ科ズイナ属に含まれます。

そのため、2種は全く異なる仲間であり、本来は2種を混同するのはあってはならないと言えるレベルに異なっています。

まず、葉に関してはリョウブでは濃緑色で、シワが少ないのに対して、コバノズイナでは鮮緑色で、シワが多いという違いがあります。

また、リョウブの葉下面の細脈は目立つのに対して、コバノズイナでは目立ちません。

花に関しては、リョウブでは花弁が長楕円形で、先はややへこみ、柱頭が薄い緑色であるのに対して、コバノズイナでは花弁が細く線形で、先はやや尖り、花全体としては星形になり、柱頭は白いか緑でも目立たないという違いがあります。

リョウブの柱頭が緑色である点は他の花に比べても特に目立つ特徴です。

果実（蒴果）に関しては、リョウブでは平たい球形で毛が密生するのに対して、コバノズイナは細長く毛は少ないという違いがあります。

References

Kanagawa Prefecture Flora Survey Association. (2018). Kanagawa Prefecture Flora 2018 Electronic Edition. Kanagawa Prefecture Flora Survey Association. ISBN: 9784991053726,https://flora-kanagawa2.sakura.ne.jp/efloraofkanagawa.html

茂木透・高橋秀男・勝山輝男・石井英美. (2003). 樹に咲く花 合弁花・単子葉・裸子植物. 山と溪谷社. ISBN: 9784635070058

Akichoji, Sekiyanoakichoji, and Yamahakka belong to the genus Mentha in the Lamiaceae family. These perennial herbs are found in forests and are notable for their remarkably long corollas compared to other members of the Lamiaceae family. While identification can sometimes be confusing, you can generally distinguish them by paying attention to the corolla and leaves. Identifying whether it is Yamahakka requires careful consideration, as there are eight species in the genus Mentha in Japan, but only Akichoji and Sekiyanoakichoji have remarkably long corollas. This article will explain the classification and morphology of the genus Mentha.

What are Akichouji, Sekiyanoakichouji, and Yamahakka?

Isodon longitubus, also known as autumn clove, is a perennial herb that grows in the shade of trees in the mountains from Gifu Prefecture westward to Kyushu in Japan (Kitamura et al., 1957).

Isodon effusus, also known as Sekiya-no-akichouji (Sekiya's Autumn Clove), is a perennial herb distributed along the Pacific coast of central Honshu, Japan (from Tochigi Prefecture to Aichi Prefecture), growing in woodlands and forest edges in hilly to mountainous areas from the Castanopsis/Oak zone to the Beech zone (Kanagawa Prefecture Flora Survey Association, 2018). Its Japanese name comes from "Sekiya," a hut where guards at checkpoints were stationed, and it was described based on a specimen from Hakone Seki in Kanagawa Prefecture (one of the checkpoints that existed during the Edo period).

Isodon inflexus, also known as mountain mint, is distributed in Hokkaido, Honshu, Shikoku, and Kyushu in Japan; the Korean Peninsula; and central to northeastern China. It is a perennial herb that grows in alluvial plains and mountainous areas from the oak and chestnut zones to the beech zone, including grasslands, forests, and forest edges.

Both belong to the genus Mentha in the Lamiaceae family, and are perennial herbs found in forests. They have remarkably long corollas and conspicuous flowers, making them stand out even among Lamiaceae plants.

Specifically, the upper lip of the corolla is strongly recurved and shallowly four-lobed, the lower lip is boat-shaped and undivided, and the stamens extend along the lower lip.

However, you might sometimes get confused about the distinction between the three types.

What are the differences between *Akichouji*, *Sekiyanoakichouji*, and *Yamahakka*?

Since there are eight known species of the genus *Mentha* in Japan alone, it's impossible to list all the identification methods here, but we will consider methods for distinguishing three of them.

What are the differences between *Akichouji*, *Sekiyanoakichouji*, and *Yamahakka*?

The biggest difference is the corolla: in *Akichouji* and *Sekiyanoakichouji*, the corolla is 16-20 mm long with a remarkably long tube, while in *Yamahakka*, the corolla is 6-7 mm long with a short tube.

Among the genus Mentha, only Mentha japonica and Mentha japonica var. sekiyanensis have remarkably long corollas.

Another difference is that while *Akichouji* and *Sekiyanoakichouji* lack dark purple spots on the upper lip of the corolla, *Yamahakka* has dark purple spots on the upper lip of the corolla.

Another difference is that in *Akichouji* and *Sekiyanoakichouji*, the calyx is bilabiate, with the upper lip being 3-lobed and shorter than the lower lip which is 2-lobed, whereas in *Yamahakka*, the calyx is almost equally 5-lobed, but confirming this point may be difficult.

Regarding the leaves, there is a difference in that the leaf tips of *Akichouji* and *Sekiyanoakichouji* elongate into a tail-like shape, while those of *Yamahakka* do not.

What is the difference between *Akichouji* and *Sekiya no Akichouji*?

Autumn jasmine and Sekiya jasmine are very similar, making them difficult to distinguish.

However, it's important to note that while *Akichouji* is distributed from Gifu Prefecture westward to Kyushu in Japan, *Yamahakka* is distributed on the Pacific side of central Honshu (from Tochigi Prefecture to Aichi Prefecture).

Therefore, identifying them by region is the easiest method.

Morphological differences include the fact that in *Akichouji*, the pedicels are short, less than 10 mm in length, and the calyx tips are blunt, while in *Sekiya-no-akichouji*, the pedicels are long, 10-25 mm in length, and the calyx tips are pointed.

It is probably impossible to distinguish them by their leaves.

References

Kanagawa Prefecture Flora Survey Association. (2018). Kanagawa Prefecture Flora 2018 Electronic Edition. Kanagawa Prefecture Flora Survey Association. ISBN: 9784991053726,https://flora-kanagawa2.sakura.ne.jp/efloraofkanagawa.html

Kitamura, S., Murata, G., & Hori, K. (1957). Illustrated Flora of Japan in Color: Herbaceous Plants, Vol. 1 (Revised Edition). Hoikusha. ISBN: 9784586300150

Petunias (Ipomoea purpurea) and calibrachoa both belong to the Solanaceae family. Originally, the genus Calibrachoa was included in the genus Ipomoea, but it is now treated as a separate genus. The two species are very closely related, making taxonomic identification extremely difficult. However, in horticultural varieties, they can be distinguished by leaf size and stickiness. However, hybrids also exist, so it may be difficult to distinguish them 100%. This article will explain the classification and morphology of the genera Ipomoea and Calibrachoa.

What are petunias and calibrachoas?

Petunia x atkinsiana, also known as the Japanese morning glory, is commonly called petunia. While the scientific name Petunia x hybrida has long been used and is almost exclusively found in Japanese books and websites, it is treated as a synonym overseas (Soares et al., 2025). It is a horticultural hybrid created by artificial crossbreeding of Petunia axillaris and Petunia integrifolia, both native to South America, and is a non-hardy perennial (usually an annual in Japan) cultivated worldwide for ornamental purposes.

Calibrachoa x hybrida is a horticultural hybrid created by crossing multiple species belonging to the genus Calibrachoa. In Japan, Suntory first introduced the Million Bells® Series in the 1990s, and since then, a great many horticultural varieties have been created. It is a non-hardy perennial (usually an annual in Japan). Calibrachoa is the name of the genus (group), so it is originally a general term for all species belonging to the genus Calibrachoa, including species such as Calibrachoa parviflora, but in general, when people say Calibrachoa in horticulture, they are referring to the group of hybrids.

Both belong to the Solanaceae family, and while the genus Calibrachoa was originally included in the genus Ipomoea, it is now treated as a separate genus (Fregonezi et al., 2013).

Because they produce beautiful fused-petal flowers and are relatively easy to cultivate, these two species are very popular in horticulture and are grown in gardens and other places around the world for ornamental purposes.

However, the two species are very closely related, and their flowers are very similar, so many people may not be able to tell the difference.

What is the difference between petunias and calibrachoas?

In conclusion, it is very difficult to distinguish between petunias (Ipomoea nil) and calibrachoas cultivated in gardens.

Academically, the genera *Ipomoea* and *Calibrachoa* have traditionally been considered separate genera based on differences in chromosome number. *Ipomoea* has n = 7 chromosomes, while *Calibrachoa* has n = 9 (Reis et al., 2002).

Other differences have also been discovered, such as the following:

However, it would be difficult to verify these points outdoors.

In practical terms, petunias have large, sticky leaves, while calibrachoa have smaller, non-sticky leaves compared to petunias (The Garden Party, 2024).

Also, petunias tend to have larger corollas.

However, in recent years, hybrids between the genera *Ipomoea* and *Calibrachoa* have increased, so it is thought that 100% distinction is not possible. This is called *Pechoa* x * Petchoa *.

Petunias are not naturally creeping plants, while calibrachoas are. However, the petunia cultivar called Surfinia is creeping, so this characteristic can no longer be used for identification.

Are there any similar species?

There are no other closely related species, but it seems that it is sometimes confused with other species that have fused petals.

Many people seem to search for the difference between vinca and petunias, but vinca has propeller-shaped flowers, so they look completely different.

What are the differences between periwinkle, climbing periwinkle (Vinca), and dwarf periwinkle? An explanation of how to distinguish between similar species – Ecological Notes Web

Periwinkle, Vinca minor, and dwarf periwinkle all belong to the Apocynaceae family and are cultivated in Japan for ornamental purposes, and are herbaceous plants that can be frequently seen even in urban areas. They are popular for their interesting fused petals that have five propeller-shaped lobes at the tip, but their names are...

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References

Fregonezi, JN, Turchetto, C., Bonatto, SL, & Freitas, LB (2013). Biogeographical history and diversification of Petunia and Calibrachoa (Solanaceae) in the Neotropical Pampas grassland. Botanical Journal of the Linnean Society, 171 (1), 140-153. https://doi.org/10.1111/j.1095-8339.2012.01292.x

Reis, CD, Sajo, MDG, & Stehmann, JR (2002). Leaf structure and taxonomy of Petunia and Calibrachoa (Solanaceae). Brazilian Archives of Biology and Technology, 45, 59-66. https://doi.org/10.1590/S1516-89132002000100010

Soares, LS, Stehmann, JR, & Freitas, LB (2025). The genus Petunia (Solanaceae): Evolutionary synthesis and taxonomic review. Plants, 14 (10), 1478. https://doi.org/10.3390/plants14101478

The Garden Party. (June 25, 2024). Easy! Compare and understand the difference between petunias and calibrachoas! The Garden Party - https://gardenparty87.jp/apps/note/flower/petunia/t20210315

Jerusalem artichoke, Helianthus tuberosus, and Helianthus retusus all belong to the Asteraceae family. They are characterized by erect stems, scales on the receptacle, and yellow ray florets, but their appearance is so lacking in distinct features that they could be described as "The Asteraceae." Distinguishing between them is difficult if you only look at the flower heads, but Jerusalem artichoke and Helianthus tuberosus are the only ones that produce tubers, and they can be distinguished by carefully observing the leaves and the involucral bracts of the flower heads. This article will explain the classification and morphology of the genera Helianthus and Helianthus retusus.

What are Jerusalem artichokes, dog Jerusalem artichokes, and false Jerusalem artichokes?

Helianthus tuberosus, also known as the Jerusalem artichoke, is a perennial plant native to North America (Canada and the United States) that has naturalized throughout the world, including Japan (RBG Kew, 2026). It was introduced to Japan around the end of the Edo period and was widely cultivated during wartime for processing and animal feed. Although it is not widely cultivated now, it can sometimes be found growing wild in the corners of fields or at the foot of mountains (Hayashi et al., 2013).

Helianthus tuberosus var. willdenowianus, also known as the dog's Jerusalem artichoke, is a naturalized population in Japan (Kanagawa Prefecture Flora Survey Association, 2018). Currently, it is rarely distinguished from other species.

Heliopsis helianthoides, also known as false Jerusalem artichoke, is a perennial plant native to North America (Canada and the United States) that has naturalized throughout the world, including Japan.

Both belong to the broad tribe Heliantheae or Heliantheae within the Asteraceae family. They are characterized by erect stems, scales on the receptacle, and yellow ray florets, but their overall appearance lacks distinct features, making them often referred to as "The Asteraceae."

However, Jerusalem artichokes and Heterocarya erythrorhizon have the unique characteristic of producing edible tubers underground, which is rarely seen in other species and can be considered their most distinctive feature.

What Native Americans called "sun root" and cultivated was spread throughout the world after European colonization (Tapera et al., 2024). It is particularly drought-resistant and highly valued as a famine food.

In Japan, inulin was cultivated from the late Edo period onward, but it never became a major food source and doesn't seem to be a significant part of daily life. However, it plays a very important role in the production of inulin.

Inulin is not digested, is completely filtered in the glomeruli of the kidneys, and is neither secreted nor reabsorbed by the renal tubules. Therefore, it is used as an indicator substance for measuring important renal function (especially glomerular filtration rate) as "inulin clearance." It is a topic that is always covered in high school biology.

Furthermore, inulin and fructooligosaccharides contained in Jerusalem artichoke tubers are expected to improve gut and blood metabolites, thus playing a role as glucose substitutes and prebiotics (Liava et al., 2021).

However, it looks very similar to the false Jerusalem artichoke, which does not produce such tubers, and is often confused with it.

What are the differences between Jerusalem artichoke, Helianthus praecox, and false Jerusalem artichoke?

These three species can be distinguished by carefully examining their leaves and flower heads (the clusters of flowers characteristic of the Asteraceae family) (Kanagawa Prefecture Flora Survey Association, 2018).

What are the differences between Jerusalem artichoke, Helicobacter jezoensis, and false Jerusalem artichoke?

First and foremost, it's important to understand that Jerusalem artichoke and Helicobacter erythrorhizon belong to the genus Helicobacterium, while false Jerusalem artichoke belongs to the genus Helicobacterium. Therefore, there are differences in their classification.

In terms of specific morphological differences, in Jerusalem artichoke and Heterocarya erythrorhizon, the lower leaves are opposite, while the upper leaves are alternate, and the fruit falls off before it is fully ripe. In contrast, in false Jerusalem artichoke, all the leaves are opposite, and the ray florets remain until the fruit is fully ripe.

Furthermore, while the serrations on the leaves of Jerusalem artichoke and Heterocarya erythrorhizon are not very prominent, they are clearly visible in Heterocarya erythrorhizon.

Furthermore, there is a difference between Jerusalem artichoke and Heterocarya erythrorhizon: the involucral bracts of Heterocarya erythrorhizon are arranged in multiple rows and are all herbaceous, while those of Heterocarya erythrorhizon are arranged in one or two rows and are herbaceous to membranous. However, this difference is a bit troublesome as it requires examining the leaf-like structures on the underside of the flower head.

As mentioned above, Jerusalem artichoke and Heterocarya erythrorhizon have tubers, but false Jerusalem artichoke does not.

What is the difference between Jerusalem artichoke and dog's Jerusalem artichoke?

In Japan, *Hercules jellyfish* is considered a wild variety of *Hercules jellyfish*, and has traditionally been distinguished from it. However, this distinction is not made in North America, where it is native, and it is a classification unique to Japan that is not considered a global view.

Furthermore, since it is known that intermediate individuals exist, a clear distinction is considered impossible.

Therefore, there will likely be no need to distinguish between Jerusalem artichoke and Heterocarya erythrorhizon in the future.

However, since it might have ecological significance, I'll briefly explain the difference here.

In contrast to Jerusalem artichoke, the leaves are dark green with distinct serrations, the flowers bloom in early summer with 10-20 ray florets that are three-lobed at the tip, and the tuber is large and rough. In contrast to Helicobacter erythrorhizon, the leaves are grayish-green with shallow and indistinct serrations, the flowers bloom from late summer to autumn with 8-15 ray florets that are not lobed at the tip, and the tuber is somewhat smaller, less rough, and spindle-shaped.

Are there any other similar species?

There are many species of yellow ray florets in the Asteraceae family, so caution is needed.

For more information on the sunflower genus, which includes Jerusalem artichokes, please see our separate article.

What are the differences between sunflowers, dwarf sunflowers, and white sunflowers? We explain how to distinguish between similar species! Is it a myth that "sunflowers face the sun"? Why are they the national flowers of Russia and Ukraine? – Ecological Notes Web

Sunflowers are said to face the sun, giving them a cheerful and bright image, and they are now a familiar plant in Japan. While there are many varieties native to North America, only a limited number of sunflower species can be found in Japan, including the common sunflower, dwarf sunflower, and dusty sunflower.

ecological-information.com

References

Hayashi, Yasaka, Kadota, Yuichi, and Hirano, Takahisa. (2013). Yamakei Handy Illustrated Guide 1: Wildflowers (Revised and Expanded New Edition). Yama-kei Publishers. ISBN: 9784635070195

Kanagawa Prefecture Flora Survey Association. (2018). Kanagawa Prefecture Flora 2018 Electronic Edition. Kanagawa Prefecture Flora Survey Association. ISBN: 9784991053726,https://flora-kanagawa2.sakura.ne.jp/efloraofkanagawa.html

Liava, V., Karkanis, A., Danalatos, N., & Tsiropoulos, N. (2021). Cultivation Practices, Adaptability and phytochemical composition of Jerusalem artichoke (Helianthus tuberosus L.): A weed with economic value. Agronomy, 11(5), 914. https://doi.org/10.3390/agronomy11050914

RBG Kew. (2026). The International Plant Names Index and World Checklist of Vascular Plants. Plants of the World Online. http://www.ipni.org and https://powo.science.kew.org/

Tapera, RF, Siwe-Noundou, X., Shai, LJ, & Mokhele, S. (2024). Exploring the Therapeutic Potential, Ethnomedicinal Values, and Phytochemistry of Helianthus tuberosus L.: A Review. Pharmaceuticals, 17(12), 1672. https://doi.org/10.3390/ph17121672

Koyabouki, Nagabano-koyabouki, and Kashiwaba-haguma all belong to the genus Koyabouki in the Asteraceae family. A major distinguishing feature of these three species, even within the vast Asteraceae family, is that the tubular florets in the center of the flower head have a two-lipped corolla. They are commonly found in forests. However, the flower heads of the three species are similar, and some people may have difficulty distinguishing them. The three species can be distinguished mainly by their life form and leaf shape. The way the leaves are attached differs depending on the maturity of the branches, so this point should be noted when identifying them. This article will explain the classification and morphology of the genus Koyabouki.

What are *Kouyabouki* and *Nagabano Kouyabouki*?

Pertya scandens, also known as Koyabouki, is a deciduous shrub distributed in Honshu (west of the Kanto region), Shikoku, and Kyushu in Japan, as well as in China. It grows in dry forests and forest edges in the areas of Castanopsis and Quercus and the lower part of the Fagus zone.

Pertya glabrescens, also known as long-leaved broom, is a deciduous shrub distributed in Honshu, Shikoku, and Kyushu in Japan, growing in dry forests and forest edges at higher elevations than the common broom.

Pertya robusta, also known as oak-leaved white bear, is a perennial herb distributed in Honshu, Shikoku, and Kyushu in Japan, growing in dry fir forests and oak-konara forests in the areas from the oak-castus zone to the lower beech zone.

Both belong to the genus *Asteraceae*, and a major distinguishing feature that allows them to be identified within the vast Asteraceae family is that the tubular florets in the center of the flower head have a two-lipped corolla. They are commonly found in forests.

However, the three types of flower heads are similar, and some people may have difficulty distinguishing them.

What are the differences between *Koyabouki*, *Nagabano Koyabouki*, and *Kashiwaba Haguma*?

The three species can be distinguished primarily by their life cycle and leaf shape.

First, they can be broadly classified into *Aster tataricus*, *Aster tataricus*, and *Aster savatieri*.

While *Koyabouki* and *Nagabano Koyabouki* may appear herbaceous at first glance, their stems are woody and have hard branches, and their leaves are small with small serrations. In contrast, *Kashiwaba Haguma* is a completely herbaceous plant with large leaves and prominent, coarse serrations.

The difference is clear, so you shouldn't have much trouble deciding.

The situation with *Koyabouki* and *Nagabano-koyabouki* is a bit more complicated. As a prerequisite, it's important to understand that the leaves on flowering branches (branches that have matured and bear flowers) and the leaves on current-year branches (branches that are newly growing in that year) differ in leaf shape and phyllotaxy between *Koyabouki* and *Nagabano-koyabouki*.

In *Aster tataricus*, the leaves on the flowering branches are alternate, hairy, and short, while the leaves on the current year's branches have five or more pairs of projection-like serrations. In contrast, in *Aster tataricus*, the leaves on the flowering branches are whorled, hairless, and long, while the leaves on the current year's branches have two pairs of projection-like serrations.

This is the origin of its Japanese name; if you see a plant with long, whorled leaves, you can assume it is *Long-leaved Koyabouki*.

However, it's important to note that even with *Aster tataricus*, some leaves on the current year's branches are relatively long.

Are there any other similar species?

The genus *Asteraceae* has few species, and there are no other species that are often confused with it.

However, Pertya x hybrida, also known as Oobakoyabouki, is a hybrid of Pertya x japonica and Pertya x oakleaf, and is rarely found in areas where Pertya x japonica and Pertya x oakleaf grow together. It resembles Pertya x oakleaf, but can be distinguished by its dispersed leaves and the fact that its flower heads are clustered at the end of the stem.

It is sometimes confused with the mole cricket, but they are completely different. Please see the separate article for more details.

What are the differences between Atractylodes macrocephala (white atractylodes), Atractylodes lancea (narrow-leaved atractylodes), and Atractylodes japonica? An explanation of how to distinguish between similar species – Ecological Notes Web

Atractylodes macrocephala (white atractylodes) and Atractylodes lancea (narrow atractylodes) are both perennial herbs belonging to the Asteraceae family, and are well-known as medicinal herbs. The dried rhizomes are collectively called "jutsu." Morphologically, the leaves have prominent serrations, and the flowers, as is typical of the Asteraceae family, are arranged in capitulum (flower heads), with only tubular florets...

ecological-information.com

References

Kanagawa Prefecture Flora Survey Association. (2018). Kanagawa Prefecture Flora 2018 Electronic Edition. Kanagawa Prefecture Flora Survey Association. ISBN: 9784991053726,https://flora-kanagawa2.sakura.ne.jp/efloraofkanagawa.html

Lindernia procumbens, Lindernia maximowiczii, and Lindernia avium are all small annual herbs belonging to the Linderniaceae family. They are characterized by opposite leaves and small, lip-shaped flowers in the leaf axils. Although they are rather inconspicuous, their flowers are very similar, making them easily confused. These three species differ in their habitat, leaves, and flowers. However, the Linderniaceae family includes many other similar species, so careful identification is necessary. This article will explain the classification and morphology of the Linderniaceae family.

What are Lindernia procumbens, Lindernia maritima, and Lindernia glabra?

Torenia crustacea, also known as melon grass, is an annual plant that grows in fields and roadsides and is distributed in Hokkaido, Honshu, Shikoku, Kyushu, and the Ryukyu Islands in Japan; as well as in Korea, China, Southeast Asia, and Micronesia (Kanagawa Prefecture Flora Survey Association, 2018).

Lindernia procumbens, also known as Azena, is an annual plant that grows in rice paddies and wetlands and is widely distributed in Honshu, Shikoku, Kyushu, and the Ryukyu Islands of Japan, as well as in tropical to temperate regions of the Northern Hemisphere.

Lindernia dubia subsp. major, also known as American dwarf moss, is a naturalized species native to North America. It has become increasingly common in various regions since the end of World War II and is an annual plant that grows in slightly damp areas such as rice paddies.

Both belong to the Linderniaceae family and are small annual plants characterized by opposite leaves, flowers in the leaf axils, a tubular calyx with 5 lobes, a bilabiate corolla with the upper lip 2-lobed and the lower lip broadly 3-lobed, and the absence of a spur.

Although it is a common wild plant that grows throughout the area, its flowers are small and inconspicuous, so they are often overlooked. Furthermore, all members of the Linderniaceae family have very similar flowers, which can lead to confusion.

What are the differences between Lindernia procumbens, Lindernia maritima, and Lindernia serrata?

The family Linderniaceae includes many species, but for now we will consider three well-known species (Hayashi et al., 2013; Kanagawa Prefecture Flora Survey Association, 2018).

As a fundamental point, within the Linderniaceae family, there is a difference in that Lindernia procumbens belongs to the genus Lindernia, while Lindernia serrata and Lindernia moniliformis belong to the genus Lindernia. Therefore, there is a gap in their classification.

In particular, the differences are that in the genus *Lindernia* (Lindernia procumbens), the calyx is shallowly 5-lobed at the tip, and the calyx lobes are shorter than the calyx tube, while in the genus *Lindernia procumbens* (Lindernia japonica and *Lindernia mongolica*), the calyx is deeply 5-lobed almost to the base, and the calyx lobes are narrowly ovate and longer than the calyx tube.

The differences at the genus level are as described above, but there are other differences if we focus on Lindernia procumbens, Lindernia maximowiczii, and Lindernia avium.

Regarding habitat, there is a difference in that *Lindernia procumbens* grows in fields and roadsides, while *Lindernia ovalifolia* and *Lindernia procumbens* grow in rice paddies and wetlands.

Regarding the leaves, there is a difference in shape: in *Lindernia procumbens*, the leaves are ovate to broadly ovate, while in *Lindernia japonica* and *Lindernia procumbens*, they are ovate to elliptical.

Regarding the flowers, *Lindernia procumbens* has a dark blue-purple pattern on the central lobe and the edges of the petals are slightly darker in color, whereas *Lindernia ovalifolia* and *Lindernia procumbens* do not have any special markings.

What is the difference between Azena and American Azena?

The biggest difference between Lindernia procumbens and Lindernia asiatica is that Lindernia procumbens leaves have indistinct serrations that are only slightly indented, while Lindernia asiatica leaves have a small number of serrations.

Other differences include the fact that in Lindernia procumbens, there are four stamens with anthers, the fruit tip is blunt and rounded, the seeds have no transverse ridges, and the edges are thickened longitudinally, forming a series of semicircular fin-like protrusions that look like curved, fine hairs under a magnifying glass, while in Lindernia maximowicziana, only two of the four stamens have anthers, the fruit tip is pointed, the seeds have transverse ridges, and the edges of the seeds do not have thickened areas.

Currently, American dwarf

Are there any other similar species?

Although the number of species in the Linderniaceae family is limited, there are more closely related species than one might think because their flowers are very similar.

Lindernia dubia subsp. dubia is a subspecies of Lindernia japonica and is very similar to it, but the base of its leaves is rounded to elliptical and clasps the stem, at least for leaves attached to the middle of the stem or higher. In Lindernia japonica, the base of the leaves is distinctly wedge-shaped and does not clasp the stem, even for leaves attached to the upper part of the stem.

Lindernia anagallidea has dense glandular hairs all over its body when young, which later remain on the flower stalks and fruits. Other Lindernia species usually do not have such prominent glandular hairs on their bodies. Like Lindernia procumbens, it is an introduced species, but there are only a few records of it.

Vandellia micrantha, a species of the genus Vandellia, has leaves with shallow, few, and inconspicuous serrations. Its fruit is 3 to 4 times the length of the calyx, giving it a chili pepper-like appearance, and its flowers have yellow markings.

The broad-leaved bell pepper (Bonnaya verbenifolia) and the branched bell pepper (Bonnaya grandiflora), both belonging to the genus Bonnaya, have leaves with numerous sharp, pointed serrations, fruits with pedicels as thick as the fruit body, and flowers that appear to be flattened sideways.

Torenia (also known as Hanaurikusa) is a cultivated variety, and while Torenia belongs to the same genus, its flowers and leaves are much larger, making them look completely different.

References

Hayashi, Yasaka, Kadota, Yuichi, and Hirano, Takahisa. (2013). Yamakei Handy Illustrated Guide 1: Wildflowers (Revised and Expanded New Edition). Yama-kei Publishers. ISBN: 9784635070195

Kanagawa Prefecture Flora Survey Association. (2018). Kanagawa Prefecture Flora 2018 Electronic Edition. Kanagawa Prefecture Flora Survey Association. ISBN: 9784991053726,https://flora-kanagawa2.sakura.ne.jp/efloraofkanagawa.html

Japanese pokeweed (Phytolacca americana), American pokeweed (Phytolacca oleracea), and Japanese pokeweed (Phytolacca japonica) all belong to the Phytolaccaceae family and Phytolacca genus. Their names come from the fact that their fleshy, thick roots resemble those of burdock (Philadelphia arvensis), a member of the Asteraceae family. They are characterized by being entirely poisonous and having blackish-purple berries. However, the three species are often confused and mistaken for burdock. The three species can be distinguished by comprehensively observing their leaves, flowers, and fruits. Burdock and Japanese holly (Phytolacca americana) are sometimes called "Japanese pokeweed," which can lead to confusion with the biological Phytolacca genus, but their leaves, flowers, and fruits are all completely different. Never eat the roots of the Phytolacca genus. There have been cases of death. However, birds readily eat the fruits. This article will explain the classification, morphology, ecology, and toxicity of the Phytolacca genus.

What are Japanese pokeweed, American pokeweed, and round pokeweed?

Phytolacca acinosa, also known as mountain pokeweed, is a perennial herb distributed in Hokkaido (southwestern part), Honshu, Shikoku, and Kyushu in Japan, as well as in China, growing in forests and forest edges (Kanagawa Prefecture Flora Survey Association, 2018). The Japanese variety is believed to have escaped cultivation after being brought from China as a medicinal herb.

American pokeweed (Phytolacca amana), also known as American pokeweed, is native to North America and was introduced to Japan in the early Meiji era. It has since spread throughout Japan and is a perennial plant that grows in vacant lots and along roadsides.

Phytolacca japonica, also known as round-fruited mountain burdock, is a perennial herb distributed in Honshu (west of the Kanto region), Shikoku, and Kyushu in Japan, growing in woodlands and forest edges.

Both belong to the Phytolaccaceae family and the Phytolacca genus. Their names come from the fact that their fleshy, thick roots resemble those of the burdock plant (Philadelphia arvensis) of the Asteraceae family. They are large perennial plants, reaching a height of 1 to 1.5 meters, and are characterized by having five sepals that resemble petals, and flowering from June to September.

American pokeweed, in particular, is frequently seen even in urban areas, but despite this, all parts of the pokeweed genus contain saponins and oxalates, making them highly toxic and capable of causing food poisoning in both humans and livestock (Xu et al., 2025).

The toxic substances are most abundant in the roots, followed by the leaves, trunk, and then the fruit (Takai, 1983). There have been fatalities in China, so you should absolutely never eat it.

The most distinctive visual feature is its oblate, spherical, dark purple berry fruit, which immediately identifies it as a member of the Phytolacca genus. The inside is divided into schizocarps.

The fruits of the genus Phytolacca are poisonous to mammals such as humans, but are non-toxic to birds. This is strongly related to the fact that birds eat the fruits and disperse the seeds, which is why they are frequently seen on concrete in urban areas (Kaneko et al., 2012; Li et al., 2017).

However, the genus Phytolacca contains three closely related species, and many people may not be able to correctly distinguish between them. Furthermore, distinguishing it from edible burdock is also essential.

What are the differences between Japanese pokeweed (Phytolacca americana), American pokeweed (Phytolacca americana var. japonica), and round pokeweed (Phytolacca americana var. japonica)?

It is difficult to distinguish between the three species based on leaves alone; a comprehensive observation of the leaves, flowers, and fruits is necessary.

What are the differences between Japanese pokeweed (Phytolacca americana), Japanese pokeweed (Phytolacca americana var. japonica), and American pokeweed (Phytolacca americana var. japonica)?

First, there is a difference between Japanese pokeweed (Phytolacca americana) and round-flowered pokeweed (Phytolacca americana var. japonica): the inflorescence stalks are short, 1-3 cm long, and erect, remaining erect even during fruiting, whereas in American pokeweed (Phytolacca americana var. japonica), the inflorescence stalks are long, 7-10 cm long, arching to drooping, and drooping during fruiting.

Furthermore, although not mentioned in the field guide, the flowers and fruits per inflorescence of Japanese pokeweed and round pokeweed appear to be quite densely packed, while the flowers and fruits per inflorescence of American pokeweed appear sparse and sparse.

Another difference is that in Japanese pokeweed, when the fruit ripens, the internal segments separate and become clearly visible, resulting in a rough appearance. In contrast, in American pokeweed and round pokeweed, the internal segments are fused together, making them invisible and resulting in a neat oval shape.

However, this is not very reliable because even in American pokeweed, schizocarps can be seen when the fruit dries. The Japanese name for round pokeweed comes from the fact that the fruit is round, but it has exactly the same characteristics as American pokeweed.

Based on the above, American pokeweed can be identified relatively easily.

In reality, what people living in urban areas mostly see is the invasive species, pokeweed (Phytolacca americana). In urban areas, you probably won't even need to worry about getting lost.

What is the difference between Japanese pokeweed (Phytolacca americana) and round pokeweed (Phytolacca americana)?

Regarding pokeweed (Phytolacca americana) and round pokeweed (Phytolacca oleracea), the differences are that pokeweed has leaves that do not have a tail-like tip, white flowers, and about 8 fruit segments, while round pokeweed has leaves that are pointed and tail-like, pale pink flowers, and about 7 to 10 fruit segments.

While that's what the botanical guide says, it's actually quite common for the flowers of *Phytolacca americana* to be white.

Therefore, distinguishing them by their leaves is the most reliable method, but since the tips of the leaves of American pokeweed are pointed like a tail, care must be taken not to confuse it with Japanese pokeweed.

While the surface of the seeds of Japanese pokeweed (Phytolacca americana) is almost smooth, that of round pokeweed (Phytolacca americana) has concentric stripes on its surface, most people probably don't need to check this detail.

Are there any other similar varieties? What's the difference between mountain burdock and regular burdock?

No other species of the Phytolaccaceae family are known in Japan, and there are no species that can be confused with them taxonomically.

However, the roots of plants such as Arctium lappa (burdock), Cirsium dipsacolepis, Cirsium borealinipponense, Synurus palmatopinnatifidus var. indivisus, and Synurus pungens var. pungens, all belonging to the Asteraceae family, are sometimes called "yamagobo" (mountain burdock) as wild vegetables. This confusion with the scientifically recognized genus Phytolacca has led to food poisoning (Takai, 1983). There have even been fatalities, so it is absolutely essential to avoid eating the roots and fruits of yamagobo (Xu et al., 2025).

Although they are often confused, both burdock and Japanese holly belong to the Asteraceae family, and are particularly related to thistles, so their leaves, flowers, and fruits are completely different.

Specifically, regarding the leaves, there is a difference in that the leaves of the Phytolacca genus are entire (without serrations, or spines), whereas those of burdock and *Phytolacca americana* have serrations.

Regarding the flowers, in the Phytolacca genus, the inflorescence is racemose, and the flowers are white to red with five sepals that resemble petals, whereas in burdock and Oyamabokuchi, the inflorescence is composed of clusters of fused-petal flowers called capitulums, and they are pink, very similar to thistles.

Regarding the fruits, Phytolacca species produce flattened, spherical, blackish-purple berries that are dispersed by birds, while burdock and Phytolacca americana have achenes with a pappus that somewhat resemble dandelion seeds (which are actually also fruits), and are dispersed by wind (or by animals).

The same applies to Cirsium japonicum, Cirsium nipponicum, and Cirsium moniliforme. Please see our other article for more information on the Cirsium genus.

What are the differences between Cirsium japonicum, Cirsium nipponicum, and Cirsium nipponicum? An explanation of how to distinguish between similar species! Did the flowers release pollen upon contact? – Ecological Notes Web

Thistles (Cirsium japonicum, Cirsium nipponicum, and Cirsium nipponicum) all belong to the Cirsium genus, and these three species are representative of those found in populated and urban areas. All three have reddish-purple flowers, and their leaves differ in shape between basal and stem leaves, and they are very thorny. The Cirsium genus is extremely common in Japan.

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How are the seeds dispersed? The poisonous berries are a favorite of birds!?

The fruits of the Phytolacca genus are berries, oblate in shape, and turn blackish-purple. The inside is divided into schizocarps, which vary depending on the species, but typically consists of 7 to 10 segments.

The berries of the genus Phytolacca are poisonous to mammals such as humans, but are non-toxic to birds, and their distribution is expanded by bird dispersal (Kaneko et al., 2012; Li et al., 2017).

In Japan, there are records of it being eaten by Japanese white-eyes, Japanese bush warblers, Arctic warblers, Japanese bush hawks, and wrens (Kaneko et al., 2012).

In China, there are records of it being eaten by the white-headed hawk (Pycnonotus sinensis) and the swan hawk (Urocissa erythroryncha) (Li et al., 2017).

It is known that birds play a major role in the spread of invasive species in urban areas (Li et al., 2017).

This type of seed dispersal is likely the result of selecting birds, which are more efficient at seed dispersal, and avoiding mammals.

In the Phytolacca genus, as the fruit ripens, the pedicel turns red, and even the small pedicels and stems after the fruit has fallen off turn a deep crimson.

This is known as "morphological bicolor" and is thought to have a conspicuous effect on birds due to its contrast (Kamitani, 1999). In fact, experiments have shown that red and black bicoloration increases the likelihood of being eaten by birds in canopy gaps rather than under a closed canopy.

References

Kaneko, Naoki; Nakata, Makoto; Chiba, Akira; and Ito, Yasuo. (2012). Autumn fruit utilization by birds in coastal forests of Niigata City. Journal of the Ornithological Society of Japan, 61 (1), 100-111. https://doi.org/10.3838/jjo.61.100

Kanagawa Prefecture Flora Survey Association. (2018). Kanagawa Prefecture Flora 2018 Electronic Edition. Kanagawa Prefecture Flora Survey Association. ISBN: 9784991053726,https://flora-kanagawa2.sakura.ne.jp/efloraofkanagawa.html

Kamitani, Tomohiko. 1999. The two-color display strategy of fruits. In: Ueda, Keisuke (Ed.), Seed Dispersal: The Evolution of Mutual Aid Vol. 1 Seeds Carried by Birds (pp. 52-63). Tsukiji Shokan. ISBN: 9784806711926

Li, N., Yang, W., Fang, S., Li, X., Liu, Z., Leng, X., & An, S. (2017). Dispersal of invasive Phytolacca americana seeds by birds in an urban garden in China. Integrative Zoology, 12 (1), 26-31. https://doi.org/10.1111/1749-4877.12214

Takai, Katsumi. (1983). Food poisoning caused by pickled pokeweed. Journal of Food Hygiene, 24 (5), 510-511. https://doi.org/10.3358/shokueishi.24.510

Xu, H., Zhou, H., Wang, Q., Wan, S., Chen, W., Hu, J., & Zhao, S. (2025). Description of a fatal case of acute Phytolacca americana poisoning due to leaf ingestion in China. Toxicon, 265, 108476. https://doi.org/10.1016/j.toxicon.2025.108476

It's common knowledge that salmon sashimi (meat), fillets, and salmon roe are red or salmon pink. You might accept this without question when you go to a sushi restaurant, play Salmon Run in the game Splatoon, or see Sanrio's KIRIMI-chan.

However, the fact that salmon flesh and roe are red is, frankly speaking, "abnormal." There are almost no other fish with red flesh or eggs (Lehnert et al., 2019). It is thought to be an evolutionary trait unique to the salmon family.

Furthermore, as will be discussed later, it has been found that having red flesh and eggs makes them easily conspicuous and therefore more susceptible to predation, resulting in significant disadvantages.

Despite this, salmon maintain their red color. Why is that? This article will explore this mystery.

To put it simply, it's thought that the carotenoid pigment that produces the red color in salmon plays a role in preventing damage to muscle cells during the strenuous movement called "anadromous migration," where salmon travel back and forth between rivers and the sea. Furthermore, male salmon with this color are considered superior, and therefore, red salmon are more attractive to mates.

The main carotenoid found in salmon is astaxanthin, a pigment whose antioxidant effects surpass those of vitamins C and E. It is known to improve overall bodily functions through its powerful antioxidant properties in humans, making it highly rational.

This article will explain why salmon sashimi (meat) and salmon roe (ikura) are red or salmon pink in color.

What kind of creature is a salmon?

What is the definition of salmon?

The word "sake" (also known as salmon, sake, stone mandarin fish, abalone, or yearly fish) generally has two meanings.

One possibility is that the insect is only poking one species of salmon (chum salmon, white salmon, autumn salmon), Oncorhynchus keta.

Another possibility is that it refers to the Salmonidae family or the genus Oncorhynchus. In addition to the genus Oncorhynchus, the Salmonidae family includes one genus, Thymallus, in the subfamily Thymallinae; three genera, Prosopium, Stenodus, and Coregonus, in the subfamily Salmoninae; and genera Brachymystax, Hucho, Parahucho, Salvelinus, and Salmo in the subfamily Salmoninae. However, there are various theories regarding classification.

Here, we will use it to mean "salmon family."

What's the difference between salmon and trout? Is it a lie that there's a difference?!

Is there a difference between salmon and trout?

In conclusion, in most cases they are the same and there is no difference.

However, in the Japanese food and beverage industry, it is customary to distinguish between wild-caught salmon that cannot be eaten raw due to parasites ("sake") and farmed salmon that are free of parasites and can be eaten raw ("salmon"). This "salmon" almost always refers to Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), or king salmon (Oncorhynchus tshawytscha).

However, for example, the salmon (chum salmon) Oncorhynchus keta, which is distributed in Japan, is called "Chum salmon" in English.

As you can see from this, there is essentially no difference that warrants special distinction.

On the internet, there are many websites that describe this practice in the Japanese food and beverage industry as if it were common knowledge, but in reality, it is a classification that applies to a very narrow field.

However, since you should be careful about food poisoning from parasites like Anisakis, please do not eat raw salmon from packages that say "salmon" on them.

What are the characteristics of salmon? What is anadromous migration?

What exactly are salmonids?

Of course, they are a type of fish, but they have the following characteristics that are not found in other fish, or that are particularly noteworthy (Willson, 1997).

• In some cases, there is an anadromous migration, a life cycle that involves moving between the sea and freshwater (rivers, ponds, lakes).
• In some cases, they exhibit a "homing" behavior, returning to the river where they were born.
• In some cases, a physiological change called "smoltization (silvering)" may occur as a result of adaptation to seawater.
• They are usually quite large in size.
• They often have a long time to reach maturity.
• They often exhibit reproductive patterns and sexual dimorphism.

However, these characteristics have essentially evolved from "anadromous migration," a type of traversal migration, and it could be said that anadromous migration is the most important characteristic.

"Through migration" refers to underwater movement that involves traveling back and forth between the sea and rivers.

"Anadromous migration" refers to the underwater movement of fish that spend most of their life cycle in the sea but spawn in rivers.

They spend most of their life cycle in the sea, but spawn in rivers. The young fish born in rivers migrate to the sea to grow, and as adults, they return to rivers to spawn. This return to the river is called "upstream migration."

Anadromous migration also includes "catadromous migration," where fish spend most of their life cycle in rivers and spawn in the sea, and "amphidromous migration," where fish utilize either the sea or rivers only for part of their life cycle.

Anadromous migration is thought to have evolved primarily when the ocean offered higher survival rates, abundant food sources, and opportunities for faster growth (Railsback et al., 2014).

The ecological behavior of anadromous migration is extremely important to the ecosystem, as bears play a role in returning nutrients from the sea to land through predation.

Why shouldn't we exterminate bears to the point of extinction? A complete explanation of the benefits of bears (Asian black bears and brown bears)! – Ecological Notes Web

In Japan, the Japanese black bear (Ursus thibetanus japonicus) is found on Honshu and Shikoku, while the Hokkaido brown bear (Ursus arctos yesoensis) is found on Hokkaido.

ecological-information.com

Furthermore, the salmonid family's most distinctive feature, its "red flesh," is thought to be related to its anadromous migration.

What are the differences between anadromous and landlocked (river-resident) types?

Here's where it gets a bit complicated: the salmon family includes not only "anadromous" species that migrate back up rivers to the sea, but also "landlocked" species or populations that do not migrate at all. The sockeye salmon, rainbow trout, cherry salmon, amago trout, and char are typical examples of this type.

Landlocked species evolved from groups that were unable to return to the sea due to glacial expansion during the last glacial period (70,000 to 10,000 years ago) and were trapped in lakes (Subramanian & Kumar, 2023).

In other words, this species originally migrated through rivers but was left stranded on land relatively recently (though this was about 70,000 years ago), resulting in its emergence as a species of fish.

However, some may selectively avoid going to sea due to reasons such as a low survival rate in the ocean (Railsback et al., 2014).

Is salmon a white-fleshed fish? Or a red-fleshed fish?

What are the differences and definitions of white-fleshed fish and red-fleshed fish?

Is salmon considered a "red-fleshed fish"? Looking at fillets or salmon sushi, you might definitely think it is.

However, the reality is different. To understand this, we need to confirm the definitions of white-fleshed fish and red-fleshed fish.

First of all, the classification of white-fleshed fish into red-fleshed fish is not based on evolution. It is simply a classification based on characteristics that are convenient for humans (Suzuki, 1976).

There is a rough definition of the difference between white-fleshed fish and red-fleshed fish: fish with white muscles and little dark muscle are called "white-fleshed fish," while fish with red muscles and a lot of dark muscle are called "red-fleshed fish."

Chemically speaking, this can be rephrased as follows: white-fleshed fish have a low myoglobin content and their flesh appears white to the naked eye, while red-fleshed fish have enough myoglobin to give their muscles a reddish color.

Typical examples of white-fleshed fish include Spanish mackerel, grunt, pufferfish, cod, and flounder.

Typical examples of red-fleshed fish include herring, sardines, mackerel, horse mackerel, flying fish, frigate mackerel, mahi-mahi, and tuna.

However, it's important to note that white-fleshed fish also contain small amounts of dark muscle, which gives them their red color, and red-fleshed fish also contain small amounts of regular muscle, which gives them their white color.

This definition doesn't have a specific indicator like "If the percentage of dark muscle is X, it's a red-fleshed fish!", but rather it's a gradient with an ambiguous boundary.

Therefore, even among red-fleshed fish, there is a range of flesh colors, from relatively pale red to quite dark red.

However, the definition of red-fleshed fish remains unchanged: it must have a high content of dark muscle and myoglobin.

Salmon is a white-fleshed fish!?

According to this definition, which category does salmon fall into?

The red color of salmon meat is simply due to the deposition of a different component called "carotenoid" from its food into its body. It has nothing to do with myoglobin.

Therefore, although it is a reddish meat and can be called "red meat," salmon is not a red-fleshed fish, but a white-fleshed fish.

Some people might be indignant and ask, "Why isn't it considered a red-fleshed fish when it's red?" but that's because it's based on this definition.

In fact, I don't think you've ever tasted iron when eating salmon at a sushi restaurant.

It is also known that farmed salmon will develop white flesh if they are not supplemented with carotenoids (Păpuc et al., 2024).

Generally speaking, the dark muscle is used for normal swimming, while the normal muscle is used for sudden movements such as pouncing on live prey or escaping from enemy attacks.

Therefore, it can be thought that white-fleshed fish have evolved to be less active normally and more focused on sudden movements when necessary, while red-fleshed fish have evolved to be more suited to prolonged swimming.

What is the mechanism behind the red color of salmon flesh and roe (ikura)?

As mentioned above, the red color of salmon flesh and roe (ikura) is caused by the absorption and deposition of carotenoids (mostly astaxanthin, with some canthaxanthin) derived from the diet into the body.

Specifically, when salmon feed on crustaceans such as krill, copepods, and amphipods, the carotenoids contained in them are absorbed into the salmon's body (Graham et al., 2021; Păpuc et al., 2024).

Normally, in other fish, carotenoids are broken down in the body if the amount exceeds what is used. However, in salmon, the gene called BCO2-l, which is responsible for this breakdown, is broken, so the carotenoids from the food are deposited directly into the flesh and roe (Lehnert et al., 2019).

In adult fish, carotenoids are absorbed, transported in the bloodstream, and then deposited in the muscles, where they bind to myofibrillar proteins such as α-actinin, making them appear red (Matthews et al., 2006).

In salmon roe (ikura), the carotenoids from the mother fish accumulate in the yolk, making it appear red.

Why are only the flesh (meat) and roe (ikura) of salmon red or salmon pink?

So why did salmon meat and eggs evolve to be red in the first place? In conclusion, there are two leading theories: the antioxidant theory and the sex selection theory, and it is likely that both of these factors work together to produce the red color. Let's consider them in order.

Antioxidant theory: To protect muscles from damage during anadromous migration.

The most plausible theory is the "antioxidant effect theory" (Lehnert et al., 2019).

It is believed that the ancestors of salmon originally underwent many stressful activities such as spawning migrations and nest building.

It has also been proposed that by utilizing red carotenoids as an antioxidant resource in muscle tissue, damage to muscle cells was reduced, and this, in turn, promoted the evolution of anadromous migration.

Indeed, when you see the footage of them fighting with other men, being attacked by bears, and struggling to swim upstream at a furious pace, it's easy to understand why they would experience such immense stress.

The reason why carotenoids are used as an "antioxidant resource" in muscle tissue is primarily because they protect muscles from oxidative damage (Shastak & Pelletier, 2023).

Carotenoids, especially astaxanthin, are known to suppress reactive oxygen species, reduce lipid peroxidation, and maintain the health of cell membranes. Muscles experience a high level of physical activity, and their membrane lipids are easily oxidized, so this protection is directly linked to maintaining muscle function.

Astaxanthin has been reported to have up to 65 times the antioxidant power of vitamin C and 50 times that of vitamin E (Ekpe et al., 2018), and is also known to suppress oxidative damage to cell membranes by up to 41% (McNulty et al., 2007), surpassing the effects of other antioxidants.

In fact, studies have shown that depletion of astaxanthin and vitamin E in Atlantic salmon negatively affects autoxidative defense and fatty acid metabolism (Bell et al., 2000).

In summary, the red color evolved to enable them to withstand extremely long-distance swimming and spawning migrations involving fasting. In this case, the red color was purely coincidental, just like with carrots.

Furthermore, in humans, astaxanthin is known to improve systemic functions, including the nervous and immune systems, through its powerful antioxidant and anti-inflammatory effects (Nishida et al., 2023).

Sexual selection theory: To be attractive

Another prominent theory is the "sex selection theory." Sex selection includes same-sex selection and opposite-sex selection, and here we are referring to opposite-sex selection.

Specifically, it has been found that female red-bodied females prefer red-bodied males. In other words, red-bodied males are more attractive.

Furthermore, even after mating, females have been observed to physiologically favor the sperm of males of the same color as themselves. It's surprising that they can do that, but this kind of physiological preference in males is widely known in evolutionary biology as "cryptic female choice." However, the physiological mechanism behind it is still not well understood.

This theory explains the evolutionary reasons behind the color red.

However, this theory doesn't adequately explain why the females are also red. If the above were true, the females' bodies and eggs shouldn't be red, but that's not the case.

This theory interprets the red color of female flesh as a "byproduct of genetic constraint," meaning that males and females share the gene that makes them red (i.e., there is a gene for red color outside of the sex chromosomes). However, such an explanation is rarely used in modern evolutionary biology.

A combined theory of antioxidant activity and sex selection.

In reality, these are not opposing theories, but rather it seems reasonable to consider that both had an influence.

In other words, after both males and females developed red bodies due to antioxidant properties, females began to prefer red males.

This might sound a bit vulgar, but for example, even among humans, skills like music and comedy are inherently excellent regardless of gender, but sometimes they can be linked to sexual attractiveness.

In salmon, too, the antioxidant properties may have originally been important, but gradually, the presence of antioxidants in males became an indicator of superiority. This may have led to a stronger tendency for red females to prefer red males and favor the sperm of males of the same color as themselves. This is a well-known biological concept known as "pre-adaptation" or "runaway theory."

Why are salmon roe (ikura) red?

What about salmon roe (ikura)?

A study investigating the correlation between carotenoid concentration in salmon roe, hatching survival rate, and resistance to a specific disease (vibrio disease) found that higher carotenoid levels were associated with higher hatching survival rates and greater disease resistance (Tyndale et al., 2008).

This is thanks to the antioxidant effects of carotenoids, as mentioned above.

Therefore, it is thought that the only reason eggs are red is due to antioxidant activity.

Why is salmon *only* red? It turns out that having red flesh has a lot of disadvantages!?

In reality, salmon pink has a lot of disadvantages.

Up to this point, I've only explained the advantages of a fish's body turning red, but in reality, having red flesh or eggs is full of disadvantages for fish (Lehnert, 2016; Lehnert et al., 2019).

Predation experiments with rainbow trout have shown that red eggs (ikura) are significantly more likely to be preyed upon than white eggs (Lehnert et al., 2019).

Certainly, from a human perspective, the red color of salmon roe might make it stand out, look beautiful, and appear delicious (though this is subjective).

In nature, when prey is clearly distinguishable by its color, it's often a "warning coloration" indicating that it's poisonous, but that's not always the case. In fact, humans and bears love it.

Furthermore, it has been pointed out that even if eggs have a high amount of carotenoids, there may be no significant benefit in survival rate, growth, immunity, or stress response unless the environment is particularly stressful or contains pathogens (Lehnert, 2016).

Saying there's no profit might give the impression that it's a break-even situation, but in reality, it involves "retaining" carotenoids throughout the body using genes, which means consuming energy for something that's essentially useless (Tyndale et al., 2008). In other words, it's a loss with zero profit.

Furthermore, high levels of carotenoids are also considered to be toxic to the plant itself (Lehnert et al., 2019).

Therefore, the only conditions under which the flesh or eggs of a fish turn red are when the aforementioned benefits (antioxidant effect, attractiveness) outweigh the disadvantages. That's why most fish have white flesh.

Why salmon are "only" red

Conversely, in most cases, the advantages of salmon outweigh these disadvantages, because they undertake intense upstream migrations that other fish do not.

Moreover, salmon have a mutation that has destroyed the BCO2-l gene, which is necessary for breaking down carotenoids, so they maintain their carotenoid intake from their feed. Therefore, they need to wait for a mutation that will revert their flesh back to white.

Salmon may be firmly destined to "live as red" due to their migratory behavior and genetic constraints.

It is also known that the capelin (Spirinchus lanceolatus), which also migrates through rivers, has very high levels of astaxanthin during the summer, though not to the same extent as salmon (Bragadóttir, 2001).

There was a salmon that had turned white!?

However, there are rare cases of people who have escaped this constraint (Lehnert et al., 2019).

For example, in the king salmon (Oncorhynchus tshawytscha), there are "red morphs" and "white morphs," which differ genetically in the amount of carotenoid deposition.

This suggests that in environments where predation rates are high for some reason, the aforementioned disadvantages (predation pressure) outweigh the inherent advantages, resulting in situations where the "white form" is partially advantageous, and thus both patterns coexist.

This raises the question of what will happen to landlocked salmon species in the future, but we don't really know yet.

References

Bell, JG, McEvoy, J., Tocher, DR, & Sargent, JR (2000). Depletion of α-tocopherol and astaxanthin in Atlantic salmon (Salmo salar) affects autoxidative defense and fatty acid metabolism. The Journal of Nutrition, 130 (7), 1800-1808. https://doi.org/10.1093/jn/130.7.1800

Bragadóttir, M. (2001). On the stability of Icelandic capelin meal [Master's thesis, Department of Food Science University of Iceland]. https://www.matis.is/media/matis/utgafa/Skyrsla_17-00.pdf

Ekpe, L., Inaku, K., & Ekpe, V. (2018). Antioxidant effects of astaxanthin in various diseases a review. Journal of Molecular Pathophysiology, 7 (1), 1-6. https://www.jmolpat.com/abstract/antioxidant-effects-of-astaxanthin-in-various-diseasesa-review-48193.html

Graham, C., Pakhomov, EA, & Hunt, BP (2021). Meta-analysis of salmon trophic ecology reveals spatial and interspecies dynamics across the North Pacific Ocean. Frontiers in Marine Science, 8, 618884. https://doi.org/10.3389/fmars.2021.618884

Lehnert, SJ (2016). Why are salmon red? Proximate and ultimate causes of flesh pigmentation in Chinook salmon [Doctoral dissertation, University of Windsor]. https://www.proquest.com/openview/d2e876656328ff473b13c20c8ad4b5d6/

Lehnert, SJ, Christensen, KA, Vandersteen, WE, Sakhrani, D., Pitcher, TE, Heath, JW, … & Devlin, RH (2019). Carotenoid pigmentation in salmon: variation in expression at BCO2-l locus controls a key fitness trait affecting red coloration. Proceedings of the Royal Society B: Biological Sciences, 286 (1913), 20191588. https://doi.org/10.1098/rspb.2019.1588

Matthews, SJ, Ross, NW, Lall, SP, & Gill, TA (2006). Astaxanthin binding protein in Atlantic salmon. Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 144 (2), 206-214. https://doi.org/10.1016/j.cbpb.2006.02.007

McNulty, HP, Byun, J., Lockwood, SF, Jacob, RF, & Mason, RP (2007). Differential effects of carotenoids on lipid peroxidation due to membrane interactions: X-ray diffraction analysis. Biochimica et Biophysica Acta (BBA) -Biomembranes, 1768 (1), 167-174. https://doi.org/10.1016/j.bbamem.2006.09.010

Nishida, Y., Berg, PC, Shakersain, B., Hecht, K., Takikawa, A., Tao, R., … & Maoka, T. (2023). Astaxanthin: past, present, and future. Marine Drugs, 21 (10), 514. https://doi.org/10.3390/md21100514

Păpuc, T., Cocan, D., Constantinescu, R., Răducu, C., LadoșI, D., LadoșI, I., … & Mireșan, V. (2024). Carotenoids in salmonid aquafeeds: a review of use and effects. Scientific Papers. Series D. Animal Science, 67 (1), 764-775. ISSN: 2285-5750, https://animalsciencejournal.usamv.ro/pdf/2024/issue_1/Art93.pdf

Railsback, SF, Harvey, BC, & White, JL (2014). Facultative anadromy in salmonids: linking habitat, individual life history decisions, and population-level consequences. Canadian Journal of Fisheries and Aquatic Sciences, 71 (8), 1270-1278. https://doi.org/10.1139/cjfas-2014-0091

Shastak, Y., & Pelletier, W. (2023). Captivating colors, crucial roles: Astaxanthin's antioxidant impact on fish oxidative stress and reproductive performance. Animals, 13 (21), 3357. https://doi.org/10.3390/ani13213357

Suzuki, Taneko. (1976). Red-fleshed fish and white-fleshed fish. Cooking Science, 9 (4), 182-187. https://doi.org/10.11402/cookeryscience1968.9.4_182

Subramanian, S., & Kumar, M. (2023). Genomic footprints of bottleneck in landlocked salmon population. Scientific Reports, 13 (1), 6706. https://doi.org/10.1038/s41598-023-34076-0

Tyndale, ST, Letcher, RJ, Heath, JW, & Heath, DD (2008). Why are salmon eggs red? Egg carotenoids and early life survival of Chinook salmon (Oncorhynchus tshawytscha). Evolutionary Ecology Research, 10, 1187-1199. https://uwindsor.scholaris.ca/server/api/core/bitstreams/a71aa19d-e7db-4401-91e9-faef4e8f30bf/content

Willson, MF (1997). Variation in salmonid life histories: patterns and perspectives (Vol. 498). US Department of Agriculture, Forest Service, Pacific Northwest Research Station. ISBN: 9780265016275, https://doi.org/10.2737/PNW-RP-498

Artemisia princeps, Artemisia japonica (Western Artemisia), Artemisia rupestris (Bitter Artemisia), and Artemisia velutipes (Matricaria) all belong to the Artemisia genus of the Asteraceae family. Many species are extremely common perennial herbs that grow dominantly in small vacant lots from urban areas to mountainous fields. A major characteristic is that the underside of the leaves is cottony and fluffy, and unusually for the Asteraceae family, they are wind-pollinated. However, because their flowers and fruits are inconspicuous, classification is difficult, and they can be hard to distinguish in the wild. The Artemisia genus is a very large group, so you need to consult a field guide for accurate identification, but for the four species, you can roughly distinguish them by the shape of the leaves and the amount of hair. Three of the species are rare on Honshu, with Artemisia princeps being almost dominant. Nowadays, their use seems to be limited to mugwort rice cakes, but Artemisia japonica is commonly used in Okinawa, and the group is actively researched for its medicinal properties. It can also be used in moxibustion. This article will explain the classification, morphology, ecology, and uses of the Artemisia genus.

What are mugwort, wormwood (Artemisia princeps), bitter wormwood, and male wormwood?

Artemisia indica var. maximowiczii, also known as mugwort, is also called Kazuzaki mugwort or mochigusa. While Artemisia princeps is sometimes seen used online, it is a synonym (former scientific name). It is a perennial herb distributed in Honshu, Shikoku, Kyushu, and the Ogasawara Islands of Japan, as well as in Korea, and grows in a wide range of areas from urban centers to mountains and fields (Kanagawa Prefecture Flora Survey Association, 2018).

Artemisia indica var. indica, also known as Okinawa mugwort or Fuchiba, is a perennial herb distributed in Honshu (west of the Kanto region), Kyushu, and the Ryukyu Islands in Japan; Korea, China, Taiwan, Southeast Asia (Thailand, Cambodia, Myanmar, Vietnam, Philippines), and South Asia, growing in areas such as construction sites and slopes along forest roads (Shimotsuke, 2014).

Artemisia absinthium, also known as bitter wormwood, is a perennial plant native to Europe, Russia, the Caucasus, West Asia, and North America, and has escaped cultivation and become naturalized all over the world, including Japan.

Artemisia japonica subsp. japonica var. japonica, also known as male mugwort, is a perennial herb distributed in Hokkaido, Honshu, Shikoku, Kyushu, and the Ryukyu Islands in Japan; as well as in Korea, China, Taiwan, the Philippines, and Afghanistan. It grows in riverbeds, grasslands, forest edges, and railway embankments. Its Japanese name is said to originate from the small size of its seeds.

All of these belong to the Artemisia genus of the Asteraceae family, and are extremely common perennial plants that predominantly grow in small vacant lots from urban areas to mountainous fields. However, Artemisia wormwood is an introduced species.

Morphologically, the underside of the leaves is cottony and fluffy, and the flower heads (inflorescences characteristic of the Asteraceae family) are usually oriented downwards (rarely upwards) and composed of tubular florets.

The most distinctive feature is that while most plants in the Asteraceae family are insect-pollinated, attracting insects with bright colors for pollination, Artemisia species have tubular florets that are wind-pollinated, relying on the wind to carry their pollen.

One theory suggests that this characteristic evolved when the ancestors of the Artemisia genus, which are closely related to the Chrysanthemum genus, moved into arid regions with fewer insects and switched to wind-pollinated flowers.

In fact, this aligns with the fact that Artemisia species can adapt and grow even in dry, concrete-filled areas.

Mugwort and its relatives have a long history of being used for food and medicine. Although they can be found everywhere these days, it seems that their use has decreased. However, I think most Japanese people have eaten mugwort mochi, which is made from mugwort. In Okinawa, mugwort is called "fuuchiba" and, despite its distinctive taste, is commonly eaten.

In addition, Artemisia princeps is also edible, but distinguishing between these plants is often very difficult in the wild, partly because their flowers are inconspicuous and their characteristics are hard to see.

What are the differences between mugwort, wormwood (Artemisia princeps), bitter wormwood, and male wormwood?

There are approximately 30 species of Artemisia in Japan alone, making it quite difficult to distinguish between them.

However, for reference purposes, we will only consider methods of distinguishing between four species here. Among these four species, *Artemisia princeps* and *Artemisia rupestris* can be clearly distinguished by carefully observing their leaves (Kanagawa Prefecture Flora Survey Association, 2018).

First, while mugwort, wormwood, and bitter wormwood have pinnately compound leaves, meaning the leaves are finely lobed like bird feathers, in contrast to muscovado, where the central leaves have shallower lobes and are usually spatulate-wedge shaped. There is a great deal of variation in the leaves, so you will need to examine several leaves, but it should be relatively easy to identify.

Furthermore, while white hairs are prominent on the leaves of Artemisia princeps, Artemisia japonica, and Artemisia glabra, there are almost no white hairs on Artemisia japonica.

Another important taxonomic difference is that while Artemisia princeps, Artemisia japonica, and Artemisia glabra produce both female and hermaphroditic flowers, Artemisia rupestris produces only female flowers and not hermaphroditic flowers. However, confirming this is limited to the flowering season and would be difficult for the average person.

Regarding the remaining three species, the differences are that in Artemisia princeps and Artemisia japonica, white hairs grow only on the underside, the pinnately compound leaves are not very finely divided, and the tips of the compound leaves are relatively sharp, while in Artemisia rupestris, white hairs grow on the upper surface as well, the pinnately compound leaves are more finely divided, and the tips of the compound leaves are relatively rounded.

Therefore, you can clearly see that wormwood is whitish in appearance.

The two species mentioned above are overwhelmingly rarer than mugwort, and the dominant species growing in towns is usually mugwort.

Artemisia japonica is more resistant to salt and drought damage than Artemisia sulphureus and can be found growing on coastlines (Iriyama, 2006).

What is the difference between mugwort and yomogi (Erigeron annuus)?

The most difficult to grow are mugwort and aster.

The only difference between Artemisia princeps and Artemisia japonica, according to field guides, is that Artemisia princeps has flower heads that are 1.2–1.8 mm in diameter, while Artemisia japonica has flower heads that are 1.8–2.5 mm in diameter. In other words, the parts that look like flowers (which are actually clusters of flowers) are larger in Artemisia princeps.

Therefore, it may be almost impossible to distinguish them outside of their flowering season.

While *Erigeron annuus* is sometimes described as a variety with wider leaf lobes, which could potentially help distinguish it, there is no specific description of how wide the leaf lobes must be to identify *Erigeron annuus*.

From a distribution standpoint, it seems that we can currently confirm that the plants found east of the Kanto region in Honshu are Artemisia princeps, while those found in Okinawa are Artemisia nipponica.

However, there is a clear difference in taste; Western mugwort is less bitter and has a softer texture, making it more suitable for eating.

While distinction is important from a culinary standpoint, mugwort and wormwood are broadly considered varieties within the species Artemisia indica. In some countries and eras, classifications treat mugwort, wormwood, and Artemisia japonica as a single species, indicating that they are an extremely closely related group (Shimono, 2014).

Are there any other similar species?

As mentioned above, there are many varieties, but if you carefully examine the shape of the leaves, you'll find that there are surprisingly few similar species. Nevertheless, you might still find it quite difficult.

Artemisia montana resembles mugwort and magnolia, but unlike them, it has almost no pseudostipules at the base of the petiole, and its flower heads are bulbous and bell-shaped. "Pseudostipules" are leaf-like structures that extend to the left and right from the base of the petiole on the plant body. This is relatively easy to identify, but the flower heads are frankly too ambiguous. It is common in Hokkaido and is usually found in high-altitude mountainous areas on Honshu, so those found in lowlands are likely to be large-sized mugwort.

Artemisia japonica var. lacinifolia resembles Artemisia japonica, but unlike Artemisia japonica, its leaves are pinnately deeply lobed, and the lobes are linear-lanceolate.

Gray wormwood (Artemisia sieversiana) resembles bitter wormwood, but unlike bitter wormwood, its leaf lobes gradually narrow and have sharp tips.

Artemisia vulgaris resembles mugwort and asterias, but is not currently listed in Japanese botanical guides. However, overseas studies have indicated its distribution in Japan, and its actual distribution is still not well understood (Shimono, 2014).

What are the differences in how to use mugwort, wormwood (Artemisia princeps), bitter wormwood, and male wormwood?

What are some uses for mugwort?

Mugwort has a distinctive aroma, and the young shoots picked in spring can be boiled and used in dishes such as blanched greens, soups, or even in kusa mochi (mugwort rice cakes) or deep-fried (Odachi & Hiyama, 2013). It can also be used to make mugwort tea.

Kusa mochi (known as yomogi mochi in the Kansai region) is said to have originated in the Heian period as a rice cake kneaded with cudweed, one of the seven spring herbs, but by the Edo period, the use of mugwort became established (Yamashita, 2019).

Moxibustion, or "kyu," uses moxa, which is an important part of the traditional East Asian medicine practice. Moxa is made from dried mugwort leaves with the downy hairs on the underside (Oda, 1984; Odachi & Hiyama, 2013). In this practice, moxa is burned on selected areas of the body surface (skin) to provide thermal stimulation, which is used for disease prevention and treatment. However, Artemisia montana (Japanese wormwood) is also used in some cases. Furthermore, since the plant distributed in China is not mugwort but Korean wormwood (Artemisia argyi), it is highly likely that this is used in countries other than China.

It has many medicinal uses, and its leaves are used as a crude drug called "gaiyo," which has hemostatic properties. Some of the gaiyo is actually mugwort, which is called Korean mugwort in China.

Young shoots and budding plants, after being dried and brewed into a tea, are traditionally used as a folk remedy for stomach ailments, abdominal pain, diarrhea, anemia, and cold sensitivity. More mature plants are also dried and added to bathwater as a bath additive to relieve lower back pain and hemorrhoids.

Mugwort is known to be highly nutritious, particularly rich in minerals and vitamins. Among vegetables, it ranks third in potassium content (after Swiss chard and parsley), second in iron content (after parsley), and eighth in beta-carotene content (Ando et al., 2022). Furthermore, mugwort is known to have strong antioxidant properties due to its high content of vitamins and polyphenols.

Its unique components include cineole, thujone, β-caryophyllene, borneol, and camphor (Odachi & Hiyama, 2013).

How can I use Artemisia princeps?

Although *Artemisia princeps* has a different distribution than *Artemisia japonica*, and is therefore used in different regions, its uses are very similar to those of *Artemisia princeps*.

In the Western Himalayas, it is called "thitepati" and is used by indigenous people to treat indigestion, chronic fever, and other liver diseases (Koul et al., 2017). In Nepal, the juice of this plant is used to treat dysentery, abdominal pain, and diarrhea. The young leaves are cooked and eaten with barley, adding color and flavor to rice.

For food, the Garo people (a tribe living in the Noklek Biosphere Reserve in Meghalaya, India) eat the tender sprouts as a vegetable.

Nepalis use the juice of the leaves to treat skin diseases, and the dried leaves and flowers are used as an insect repellent.

In Okinawa, it is called Fuchiba, and in the Ryukyuan language, it means "ba (leaf) that cures Fuchi (wind: illness)," which translates to "wind leaf" in Japanese. It has been widely used in households as a medicinal herb because it is believed to be effective in reducing fever, gastrointestinal diseases, and gynecological diseases (Japan Society for Food Science and Technology, 2021).

In cooking, it is often used in dishes such as Fuchiba Jushi (rice cooked with mugwort) and Boroboro Jushi (rice porridge with mugwort) (Watanabe, 2008; Japan Society for Food Science and Technology, 2021). Jushi refers to rice porridge. Its use varies by region.

In addition, it is sometimes added raw to Okinawa soba, and when used in hijaa-jiru (goat soup), it serves to mask the odor.

The reason why Artemisia japonica can be readily eaten raw may be because its leaves are more fragrant than those of Artemisia sylvestris (Yamashita, 2019) and easier to eat.

Chemically, it contains volatile oils such as β-thujone, hernialin, 1,8-cineole, estragole, savinyl acetate, ciscrisanthenyl acetate, dabanone oil, and terpineol, and possesses antifungal properties (Koul et al., 2017). Two novel compounds, trans-ethyl cinnamate and piperitone, have been isolated by chromatographic distillation.

How can wormwood (Artemisia princeps) and mugwort (Artemisia rupestris) be used?

Wormwood is an introduced species and therefore has no traditional uses in Japan, but it has a history of being used in Europe and Turkey for medicinal purposes similar to mugwort (Koul et al., 2017). It is too bitter to eat raw and is used in the herbal liqueur "absinthe."

Scientifically, its antiparasitic, antibacterial, antioxidant, and hepatoprotective properties have been proven, and experimentally, wormwood essential oil has shown antibacterial activity against budding yeast and Candida albicans.

Although Artemisia princeps is not widely used in Japan, the same subspecies found overseas has been widely used in folk medicine to treat eczema and fever.

How is pollination done?

Artemisia plants typically produce large conical inflorescences at the tips of their stems, bearing numerous small flower heads that hang downwards. The flower head is a structure unique to the Asteraceae family; it is not a single flower, but rather an inflorescence (a cluster of flowers). It consists of countless tiny flowers (florets) that may possess stamens and pistils.

There are two types of florets: ray florets and disc florets. However, in mugwort, only disc florets are present, and within these disc florets, the inner part of the flower head contains bisexual flowers (with both stamens and pistils), while the outer part contains female flowers (with only pistils).

As mentioned above, it is unusual for a member of the Asteraceae family to be wind-pollinated (Shimono, 2014; Yamashita, 2019). However, insect-pollinated varieties were also confirmed in 2022 (Hussain et al., 2024).

Regarding pollen, while animal-pollinated pollen sometimes has spines on its surface, Artemisia pollen is smooth, which is thought to be advantageous when dispersed by wind (Bolick, 1990).

What are the seed dispersal methods?

The fruits of the Artemisia genus are obovate achenes, glabrous or hairy. They lack pappus or have very short hairs. The seeds are contained within the very small achenes, resulting in a very high yield.

Therefore, it is thought that there is no special method of seed dispersal, but because the fruit and the seeds inside are very small and the yield is very high, it is thought that, at least in the case of wormwood, it is easily dispersed by water and animals in addition to gravity (Goud et al., 2015).

References

Ando, Masaya; Ogata, Ayano; Kuronuma, Takanori; Matsumoto, Takeshi; and Watanabe, Hitoshi. (2022). Evaluation of domestically produced mugwort varieties for food use. Journal of the All Japan Acupuncture and Moxibustion Society, 72 (1), 68-78. https://doi.org/10.3777/jjsam.72.68

Bolick, MR (1990). The pollen surface in wind-pollination with emphasis on the Compositae. In M. Hesse, & F. Ehrendorfer (Eds.), Plant Systematics and Evolution Vol. 5: Morphology, Development, and Systematic Relevance of Pollen and Spores (pp. 39-51). Springer. https://doi.org/10.1007/978-3-7091-9079-1_4

Goud, BJ, Dwarakanath, V. & Swamy, BC (2015). A review on history, controversy, traditional use, ethnobotany, phytochemistry and pharmacology of Artemisia absinthium Linn. International Journal of Advanced Research in Engineering and Applied Sciences, 4 (5), 77-107. https://indianjournals.com/article/ijareas-4-5-008

Hussain, M., Thakur, RK, Khazir, J., Ahmed, S., Khan, MI, Rahi, P., … & Mir, BA (2024). Traditional uses, phytochemistry, pharmacology, and toxicology of the genus Artemisia L.(Asteraceae): A high-value medicinal plant. Current Topics in Medicinal Chemistry, 24 (4), 301-342. https://doi.org/10.2174/1568026623666230914104141

Iriyama, Yoshihisa. (2006). Artemisia japonica. Journal of the Japanese Society of Landscape Architecture, 31 (4), 449. ISSN: 0916-7439, https://www.jsrt.jp/pdf/dokomade/31-4otokoyomogi.pdf

The Japanese Society for Food Science and Technology. (2021). Traditional Japanese Home Cooking: Donburi, Zosui, and Okowa. Agricultural, Forestry and Fisheries Culture Association. ISBN: 9784540191824

Kanagawa Prefecture Flora Survey Association. (2018). Kanagawa Prefecture Flora 2018 Electronic Edition. Kanagawa Prefecture Flora Survey Association. ISBN: 9784991053726,https://flora-kanagawa2.sakura.ne.jp/efloraofkanagawa.html

Koul, B., Taak, P., Kumar, A., Khatri, T., & Sanyal, I. (2017). The Artemisia genus: A review on traditional uses, phytochemical constituents, pharmacological properties and germplasm conservation. Journal of Glycomics & Lipidomics, 7 (1), 142. https://doi.org/10.4172/2153-0637.1000142

Odachi, Junko & Hiyama, Keiichiro. (2013). On the effects and uses of mugwort (Artemisia princeps). Tezukayama University Faculty of Contemporary Life Studies Bulletin, 9, 1-9. ISSN: 1349-7073, https://tezukayama.repo.nii.ac.jp/records/777

Oda, Ryuzo. (1984). Research on moxa (I): Recent manufacturing processes and the raw material, mugwort. Journal of the All Japan Acupuncture and Moxibustion Society, 33 (4), 427-430. https://doi.org/10.3777/jjsam.33.427

Shimono, Yoshiko. (2014). Artemisia indica Willd. var. maximowiczii (Nakai) H. Hara: From the perspective of a greening plant. Grass and Greenery, 6, 23-31. https://doi.org/10.24463/iuws.6.0_23

Yamashita, Tomomichi. (2019). Mugwort in Everyday Life. Nature Conservation, 568, 18-19. ISSN: 0386-4138, https://www.nacsj.or.jp/magazine/14752/

Watanabe, Yoshio. (2008). Dictionary of Okinawan Folklore. Yoshikawa Kobunkan. ISBN: 9784642014489

Linaria japonica, Linaria verum, and Linaria serrata all belong to the Plantaginaceae family and are herbaceous plants that bear cute, blue-colored "lip-shaped flowers" (flowers with separate upper and lower lips) with a swollen lower lip. Although they are introduced species, they are frequently seen in urban areas, and you might get confused if you only focus on the flowers. However, if you observe the flower color and leaf shape, you will see that they are clearly different. The flowers are very conspicuous, but surprisingly, the rate of self-pollination is high, and it is thought that almost all species in the Linaria genus are self-pollinating. This article will explain the classification, morphology, and ecology of the Linaria and Linaria genera.

What are *Linaria japonica*, *Linaria cantoniensis*, and *Linaria thunbergii*?

Nuttallanthus canadensis, also known as pine-leaved toadflax, is an annual plant native to the Americas (Canada to Argentina) that has naturalized in Japan (west of the northern Kanto and Hokuriku regions), Russia, India, and Korea (RBG Kew, 2026). It was first collected in Kyoto City in 1941 (Shimizu et al., 2001), and quickly naturalized in port areas along the Kinki region and the Seto Inland Sea, spreading northward between 1988 and 2001 (Kanagawa Prefecture Flora Survey Association, 2018).

Nuttallanthus texanus, also known as large-leaved toadflax, is an annual plant native to North America (Canada and the United States) that has naturalized in Japan and northern South America. Its distribution within Japan is unclear due to ambiguity in distinguishing it from Toadflax japonica (Kanagawa Prefecture Flora Survey Association, 2018), but it may resemble Toadflax japonica.

Cymbalaria muralis, also known as ivy-leaved toadflax, is a climbing perennial plant native to the Mediterranean region (France, Switzerland, Italy, Austria, and the former Yugoslavia) and has naturalized worldwide, including in Japan. In Japan, it was introduced during the Taisho era (1912-1926) for ornamental purposes and planted in rock gardens, but escaped cultivation and naturalized, growing along roadsides and in crevices of stone walls in residential areas throughout Hokkaido and Honshu (Shimizu et al., 2001).

All of these plants belong to the Plantaginaceae family and share the common characteristic of being herbaceous plants that bear "lipped flowers" (flowers with separate upper and lower lips) with a swollen lower lip in the center, often in shades of blue. These swollen labiate flowers are also called "mask-shaped corollas" or "mask-shaped flowers."

Other morphological features include a bifurcated upper lip of the corolla and an elongated spur at the base of the corolla.

Although it's an introduced species, it's frequently seen in urban areas, but if you only focus on the flowers, you might get confused.

What are the differences between *Linaria japonica*, *Linaria cantoniensis*, and *Linaria scabra*?

As a fundamental point, while *Linaria japonica* and *Linaria canadensis* belong to the genus *Linaria*, *Linaria scaber* belongs to the genus *Linaria japonica*.

Therefore, there are significant differences both morphologically and ecologically (Kanagawa Prefecture Flora Survey Association, 2018).

While *Linaria japonica* and *Linaria japonica var. japonica* are annuals with cylindrical stems, linear leaves, and blue flowers, *Linaria thunbergii* is a perennial with thread-like stems, palmate leaves, and purple flowers.

The term "palmate" means "hand-shaped," and in *Linaria japonica*, the leaves are clearly spread out like a palm, but in *Linaria japonica* and *Linaria verum*, they are not, and are closer to ordinary leaves that we commonly see.

Because the ivy-leaved toadflax is specialized to creep along the ground in the gaps of stone walls, its stems are extremely thin.

The field guide states that the difference between Linaria japonica and Linaria maximowicziana is that in Linaria japonica, the corolla (excluding the spur) is 6-10 mm long and the fruit has scattered projections, while in Linaria maximowicziana, the corolla (excluding the spur) is 10-14 mm long and the fruit has densely packed projections.

However, this alone might feel a little vague.

Further comparison reveals that while *Linaria japonica* produces 1 to 4 (up to 7) flowers per stem, *Linaria gracilis* produces 1 to 13 (up to 30) flowers (Flora of North America Editorial Committee, 2019).

Furthermore, while the lower lip of *Linaria japonica* is clearly white in the center, *Linaria japonica* remains blue, although it is slightly whitish.

When you actually look at the photos, you'll find that the differences are much bigger than you might have thought.

How is it pollinated? Despite its showy flowers, it seems to be entirely self-pollinating!?

How do *Linaria japonica* and *Linaria japonica* get pollinated?

The blue, mask-like flowers of the Linaria genus, though small, are striking in appearance, so one might assume they are insect-pollinated and reproduce through cross-pollination.

However, studies in the United States have shown that, contrary to appearances, all species of the genus Linaria are self-compatible and capable of self-pollination (pollination by pollen from the stamens of the same flower reaching the pistil), producing both cleistogamous and open flowers (Crawford, 2003; Crawford & Elisens, 2006).

Furthermore, cleistogamy occurs frequently, and many flowers complete self-pollination. Pollination occurs in closed flowers without any intervention, and in open flowers before they open.

Cleistogamous flowers are inconspicuous and rarely seen, but they are formed during the early and late stages of a plant's life cycle.

Therefore, despite being a very conspicuous flower, it is believed that most of them do not rely on insect pollination. This is a very surprising result.

The amount and composition of nectar are unknown, but nectar has not been observed in flowers cultivated in greenhouses or growing rooms.

There are a few insects that visit the open flowers; some observations indicate that honeybees and members of the family Carangidae visit them (Wolfe & Sellers, 1997), while others report that butterflies and possibly true bugs (Crawford, 2003).

Thus, because the genus Linaria incorporates only small amounts of other genes, it exhibits low genetic diversity, does not hybridize with other species, and significant population differentiation has been revealed through genetic studies. This is thought to be due to geographical isolation in North America (river, sea level rise, paleogeography).

It seems that this strong self-pollination strategy is related to the fact that the genus Linaria is able to thrive in urban areas of Japan.

By the way, why does it produce so many "seemingly useless flowers" like the open-flowered variety, even though it's entirely self-pollinating?

The study revealed that open flowers produce more seeds than cleistogamous flowers. This indicates that open flowers are more reproductively efficient than cleistogamous flowers, even without cross-pollination by insects.

In addition to this, it could be interpreted as a compromise that doesn't completely rule out the possibility of cross-pollination in case the environment changes.

How is the ivy-leaved toadflax pollinated?

On the other hand, what about the purple, mask-like flowers of the ivy-leaved toadflax?

In fact, research in France has shown that the same thing happens with *Linaria japonica*, with cleistogamous pollination occurring and self-pollination also taking place (Desaegher, 2017; Desaegher et al., 2017).

The exact ratio is unknown, but it is thought to be less extreme than in the genus Linaria, and is believed to involve a combination of cross-pollination and self-pollination.

However, it has been found that the flowers tend to be slightly smaller and the amount of pollen is lower in urban areas than in rural areas, and that the tendency for self-pollination is higher in urban areas of the ivy-leaved toadflax.

The specific pollinating insects found were small bees (such as Lasioglossum) accounting for 48.2%, bumblebees for 29.6%, and a small number of other large bees, honeybees, and syrphidae visiting the flowers.

Although these flowers are very similar, it can be said that the pollination tendencies of Linaria japonica and Linaria veitchii are different.

What are the seed dispersal methods?

The fruits of the genus Linaria are capsules, nearly spherical to oblong-ovate, with thin, hard walls that split open into 4-5 chambers when mature. The seeds are black, radially symmetrical, and prism-shaped with 4-7 corners.

It is believed that the genus Linaria primarily relies on gravity dispersal or wind dispersal (Crawford & Elisens, 2006).

The fruit of *Linaria japonica* is a capsule, spherical in shape with a diameter of 5-6 mm, hanging down by a long stalk, and splitting open when ripe. The seeds are less than 1 mm in diameter, black to brown in color, and have irregular wrinkles.

Toadflax is also treated as a form of gravity dispersal (Benvenuti et al., 2016).

References

Benvenuti, S., Malandrin, V., & Pardossi, A. (2016). Germination ecology of wild living walls for sustainable vertical gardens in urban environment. Scientia Horticulturae, 203, 185-191. https://doi.org/10.1016/j.scienta.2016.03.031

Crawford, PT (2003). Biosystematics of north American species of Nuttallanthus (Lamiales) [Doctoral dissertation, The University of Oklahoma]. https://www.proquest.com/openview/665d70305b3b2aa318f19aae12ba6adf/1?pq-origsite=gscholar&cbl=18750&diss=y

Crawford, PT, & Elisens, WJ (2006). Genetic variation and reproductive system among North American species of Nuttallanthus (Plantaginaceae). American Journal of Botany, 93 (4), 582-591. https://doi.org/10.3732/ajb.93.4.582

Desaegher, J. (2017). Urbanization effects on floral morphology and plant-pollinator relationships [Doctoral dissertation, Paris-Saclay University]. https://theses.hal.science/tel-01665328/

Desaegher, J., Nadot, S., Dajoz, I., & Colas, B. (2017). Buzz in Paris: flower production and plant–pollinator interactions in plants from contrasted urban and rural origins. Genetica, 145 (6), 513-523. https://doi.org/10.1007/s10709-017-9993-7

Flora of North America Editorial Committee (Eds.). (2019). Flora of North America (Vol. 17 Magnoliophyta: Tetrachondraceae to Orbobanchaceae). Oxford University Press. ISBN: 9780190868512, https://floranorthamerica.org/Main_Page

Kanagawa Prefecture Flora Survey Association. (2018). Kanagawa Prefecture Flora 2018 Electronic Edition. Kanagawa Prefecture Flora Survey Association. ISBN: 9784991053726,https://flora-kanagawa2.sakura.ne.jp/efloraofkanagawa.html

RBG Kew. (2026). The International Plant Names Index and World Checklist of Vascular Plants. Plants of the World Online. http://www.ipni.org and https://powo.science.kew.org/

Wolfe, LM, & Sellers, SE (1997). Polymorphic floral traits in Linaria canadensis (Scrophulariaceae). American Midland Naturalist, 138 (1), 134-139. https://doi.org/10.2307/2426661

Shimizu, K., Morita, H., & Hirota, S. (2001). Illustrated Guide to Naturalized Plants of Japan: 600 Species of Plant Invaders (Revised). National Rural Education Association. ISBN: 9784881370858