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

Plantain, broadleaf plantain, and budded plantain all belong to the Plantaginaceae family and the Plantaginaceae genus, and are perennial herbs that grow very commonly along roadsides. They prefer compacted ground and are known as a type of "footprint plant." These are often confused, but they can be distinguished relatively easily by paying attention to the shape of their leaves and inflorescences. In addition, the shapes of their flowers differ greatly due to differences in their pollination methods. Psyllium is a member of the Plantaginaceae genus and is used as a health food, but it has a completely different appearance in that it has stems and leaves. Some research has also been done on how it becomes stronger when trampled. This article will explain the classification, morphology, and ecology of the Plantaginaceae genus.

What are Plantago major, Plantago lanceolata, and Plantago buddingana?

Plantago asiatica var. asiatica, also known as plantain, is a perennial herb distributed in Hokkaido, Honshu, Shikoku, Kyushu, and the Ryukyu Islands in Japan; as well as in East Asia, Eastern Siberia, Indochina, and Malaysia, growing in sunny locations such as roadsides, wastelands, and lawns (Kanagawa Prefecture Flora Survey Association, 2018). Plantago asiatica var. densiuscula is a synonym (former scientific name).

Plantago lanceolata, also known as broad-leaved plantain, is native to Europe and has naturalized widely throughout the world, including Japan. It is a common perennial plant found on riverbanks, embankments, and wastelands.

Plantago virginica, also known as budded plantain, is native to North America and has naturalized in Japan, China, Taiwan, and Korea. It is a fairly common perennial plant found along roadsides. In Japan, there is a record of it being collected in Aichi Prefecture in the 1910s.

Both belong to the Plantaginaceae family, genus Plantago, and are perennial plants that grow very commonly along roadsides.

However, it doesn't grow just anywhere; it prefers ground compacted by animal, especially human, foot traffic, and is known as a type of "footprint plant." This is perhaps the most distinctive feature of this species.

Morphologically, they share several characteristics: radially symmetrical flowers, fruits that always split laterally (capsules), underdeveloped stems, and only basal leaves.

However, many people may not be able to distinguish between the three types.

What are the differences between Plantago major, Plantago lanceolata, and Plantago serrata?

Distinguishing between the three species, Plantago major, Plantago lanceolata, and Plantago asiatica, is relatively easy (Kanagawa Prefecture Flora Survey Association, 2018).

First, in plantain, the base of the leaf blade narrows abruptly, becoming wedge-shaped to truncate to rounded, with a clear boundary between the leaf blade and petiole. In contrast, in broadleaf plantain and budded plantain, the base of the leaf blade gradually narrows, becoming narrow and long, with a less distinct boundary between the leaf blade and petiole.

Regarding Plantago lanceolata and Plantago asiatica, the difference is that Plantago lanceolata has a very dense inflorescence that is a thick cylindrical shape about 1 cm wide with flowers, while Plantago asiatica has a somewhat sparser inflorescence that is a slender spike up to 6 mm wide with flowers.

Morphologically, this should be sufficient for distinguishing them. There are 11 other species of the Plantago genus known in Japan, but the three species mentioned above are overwhelmingly dominant on the mainland, so we will omit them here.

What are the differences in the flowers and pollination methods of plantain, broadleaf plantain, and bud plantain? They all have different methods!?

The differences between Plantago major, Plantago lanceolata, and Plantago asiatica are not limited to these characteristics; there are also significant differences in their ecology (Hayashi et al., 2013; Primack, 1978; Abrahamczyk et al., 2020).

Plantain flowers are enclosed in four sepals and one bract, and they bloom from the bottom to the top of the inflorescence. They are protandrous, with the stigma emerging first from between the sepals for fertilization, after which the four stamens extend. This is a characteristic of wind-pollinated flowers that prevent self-pollination and rely on cross-pollination.

The flowers of the broadleaf plantain are whitish, and the filaments of the stamens are up to 10 mm long, protruding outside the flower. This is to attract insects with pollen, and it is a characteristic of insect-pollinated flowers that relies on cross-pollination.

The flowers of Plantago major have a corolla 2.5-3 mm long, pale yellowish-brown, and deeply 4-lobed. They are cleistogamous flowers, meaning the lobes do not open, and the stamens are inside the corolla and not exposed outside the flower. This is characteristic of flowers that self-pollinate and do not rely on cross-pollination. However, there are exceptions, with slightly less than 10% of plants producing open flowers that do not bear fruit (Kanagawa Prefecture Flora Survey Association, 2018).

Interestingly, their pollination methods differ significantly. This indicates that these three seemingly similar species have completely different ecological characteristics.

Therefore, it seems likely that the likelihood of survival differs depending on whether the environment is full of insects, open and windy, or has few insects or wind.

What is the difference between plantain and cyllium?

The difference between plantain and psyllium is also a frequently searched topic. This is likely because psyllium husk, which is made from the seed coat of psyllium, is popular as a supplement for constipation and weight loss (Nakagawa et al., 1999; Kimura, 2021). Psyllium husk is rich in dietary fiber and swells significantly when it absorbs water, and is also included in laxatives. There are also reviews stating that it can be added to food to make it more palatable.

The standard Japanese name for psyllium is Plantago indica, also known as narrow-leaved plantain (or branched plantain). It is sometimes called Plantago psyllium, but this is a synonym (old scientific name). The name psyllium comes from this old scientific name. In Japan, it is sometimes called Plantago arearia, but this is a synonym overseas.

Psyllium is distributed in western Eurasia and northern Africa, but it does not grow naturally in Japan.

The crucial morphological difference between the three species mentioned above, including plantain, and psyllium is that the three species lack stem leaves (leaves growing from the stem), while psyllium does.

While plantain is sometimes used as a herbal medicine, it is not known to have the same effects as psyllium husk.

What is the mechanism by which plantain becomes resistant to being "stomped on"?

It is relatively well known that plantain species are resistant to being trampled. The three species introduced here—plantain, broadleaf plantain, and budded plantain—are all known to be resistant to being trampled and are considered "trodden plants" (Mariko et al., 2014).

A study comparing the reproduction of plantain in compacted land and tilled land showed that plantain preferred compacted land and could not reproduce sufficiently in tilled land (Matsushima et al., 2006).

This fact indicates that adaptation to compacted land is occurring at the expense of adaptation to tilled land (a trade-off).

This is beneficial for humans as well, because even though it doesn't grow in fields, it helps to solidify the soil and create green spaces (Matsushima et al., 2008), and native plantain species are attracting attention as greening plants (Hishinuma et al., 2016).

The way they stubbornly survive being trampled is inspiring and inspiring, but what mechanism allows them to acquire this resistance to being stepped on?

One study showed that being stepped on experimentally alters plant morphologies advantageous for survival and reproduction, such as an increase in the number of flower stalks and leaves, a decrease in flower stalk length, and an increase in petiole thickness, and that ethylene production occurs immediately after being stepped on (Haruhara et al., 2000). Ethylene is a type of plant hormone that is known to promote plant growth, aging, and maturation.

In other words, it seems that after being stepped on, the cells secrete ethylene as a "compensatory mechanism," which promotes cell division.

However, for this effect to work, the roots must reach deep enough and soil moisture must be retained near the surface (Matsushima et al., 2006), so it is probably not a universal method that will allow plants to survive anywhere.

References

Abrahamczyk, S., Dannenberg, LS, & Weigend, M. 2020. Pollination modes and divergent flower traits in three species of Plantago subgenus Plantago (Plantaginaceae). Flora 267: 151601. https://doi.org/10.1016/j.flora.2020.151601

Haruhara, Yukari; Tsukakoshi, Satoru; Murata, Yoshihiro; Sakurai, Naoto; Nakamura, Koji; Noma, Yutaka; and Takahashi, Eikichi. 2000. Morphological changes and ethylene production in plantain due to trampling. Weed Research 45(Supplement): 184-185. https://doi.org/10.3719/weed.45.Supplement_184

Hayashi, Yasaka, Kadota, Yuichi, and Hirano, Takahisa. 2013. Yamakei Handy Illustrated Guide 1: Wildflowers (Revised and Expanded New Edition). Yama-kei Publishers, Tokyo. 664pp. ISBN: 9784635070195

Hishinuma, S., Kojima, H., Kotani, K., & Shimada, M. 2016. Trample resistance experiment of native species greening mats using Plantago asiatica L.. Journal of the Japanese Society of Landscape Architecture 42(1): 191-194. https://doi.org/10.7211/jjsrt.42.191

Kanagawa Prefecture Flora Survey Association. 2018. Kanagawa Prefecture Flora 2018 (Electronic Edition). Kanagawa Prefecture Flora Survey Association, Odawara. 1803pp. ISBN: 9784991053726

Kimura, Masanori. 2021. Learning about herbs beneficial for gut health: The footpath plant "Plantain". Medical Herb 55. https://www.medicalherb.or.jp/archives/182131

Mariko, Noriko; Nishinari, Noriko; and Mariko, Shigeru. 2014. Population distribution of native and introduced plantain species under different land-use types with trampling disturbance and shading stress. Hosei University Tama Research Reports 29: 9-16. https://doi.org/10.15002/00010288

Matsushima, Kenichi; Tamai, Fujio; and Fukuyama, Masataka. 2006. Can plantain grow in tilled soil?. Abstracts of the Japan Society of Crop Science Conference 222: 256. https://doi.org/10.14829/jcsproc.222.0.256.0

Matsushima, Kenichi; Tamai, Fujio; and Fukuyama, Masataka. 2008. Differences in seed germination and dormancy of Plantain growing on rice paddy levees and in footpaths. Weed Research 54(1): 17-20. https://doi.org/10.3719/weed.54.17

Nakagawa, Yasue; Harashima, Emiko; Mori, Takayoshi; Sato, Manabu; and Tsuji, Keisuke. 1999. Effects of psyllium powder beverage intake on stool in adult women. Journal of the Japanese Society for Food Science and Technology 46(11): 704-709. https://doi.org/10.3136/nskkk.46.704

Primack, RB 1978. Evolutionary Aspects of Wind Pollination in the Genus Plantago (Plantaginaceae). New Phytologist 81(2): 449-458. https://doi.org/10.1111/j.1469-8137.1978.tb02650.x

トラノオスズカケは西日本を中心に分布し、環境省では指定はないものの、各都道府県で、絶滅危惧種として指定されている多年草です。個体数がとても少ないことが絶滅危惧種として指定されている理由ですが、なぜ個体数が少ないかはよく分かっていないようです。トラノオスズカケは西日本が分布の中心ですが、なぜか東京都の自然教育園での分布が確認されています。自然教育園では長年絶滅したと思われていましたが、2007年に再発見されました。自然教育園に分布してるのは、本草学に詳しい平賀源内が持ち込んだためという説もありますが、可能性はあるものの、残念ながら直接の証拠はありません。トラノオスズカケの花序は短い穂状花序でこのことが名前の由来となっています。どのように受粉しているのかについては分かりませんが、ホソヒラタアブのようなハナアブが関係しているかもしれません。果実は蒴果で、種子は光発芽の性質が強く、強い休眠性を持つことが確認されています。 This article will explain the distribution, history, pollination ecology, and seed dispersal of the tiger's-legged plane tree (Platanthera japonica).

A rare species found in localized areas.

Veronicastrum axillare, also known as Tiger's Tail Bellflower, is a warm-climate perennial herb belonging to the Plantaginaceae family, distributed only in the lowlands of the Tokai, southern Shikoku, and Kyushu regions, and inhabiting forests (Satake et al., 1999). In recent years, it has also been discovered in Tottori Prefecture (Nagamatsu et al., 2016). Its distribution has also been confirmed in the National Garden for Nature Education in Tokyo, where it was only found between 1915 and 1948, but was rediscovered in 2007 after a 59-year absence (Hagiwara, 2014). The following photos were also taken in the National Garden for Nature Education.

The Japanese name comes from its resemblance to Veronicastrum villosulum, an endangered species in Tokushima Prefecture, and the likening of its inflorescence to a tiger's tail. The name Suzukake is said to originate from the fact that its small, clustered spike-like inflorescence resembles the "suzukake," a part of the attire worn by yamabushi (mountain ascetics who practice Shugendo in the mountains).

The leaves are alternate, hairless, glossy, 5-10 cm long, and have triangular serrations. A distinctive feature is that it produces vine-like stems that touch the ground and develop adventitious roots.

Why did they become endangered species?

It is extremely rare and listed in the Red Data Book of each prefecture. In most cases, its habitat is kept secret for conservation reasons.

As of 2021, although it is not listed in the Ministry of the Environment's Red Data Book, it is classified as Vulnerable (VU) in Shizuoka Prefecture, Extinct in Okayama Prefecture, Critically Endangered (CR) in Ehime Prefecture, Near Threatened (NT) in Kochi Prefecture, Critically Endangered (CR) in Fukuoka Prefecture, and Near Threatened in Kagoshima Prefecture (Wildlife Research Association/Envision Environmental Conservation Office, 2021).

In all cases, the reason for the designation is a small population size, but the exact cause of this small population size is not well understood. However, it is possible that the population size was already small to begin with, and that it has been affected by human development.

Why is there a Veronica serrata in the Tokyo Metropolitan Institute for Nature Education?

At the National Museum of Nature and Science's Natural Education Garden in Shirokanedai 5-chome, Minato-ku, Tokyo, *Platanthera japonica* was first recorded in 1915 and reconfirmed in 1932 by the renowned botanist, Tomitaro Makino.

However, after being discovered in 1948 by plant sociologist Tokio Suzuki, it was thought that the plant had disappeared from the National Garden for Nature Education.

Although it had not been seen for many years, it was rediscovered in 2007 by Shinsuke Hagiwara of the same nature education park, after a 59-year absence.

The reason why *Platanthera hologlottis* has been absent for such a long period is thought to be because its habitat became covered by *Pleioblastus chino*, and the recent mass die-off of *Cornus controversa* due to the yellow-legged tussock moth has restored sunlight, allowing the plants to germinate.

By the way, *Platanthera japonica* is usually distributed mainly in western Japan. However, as mentioned above, it has been found in an isolated location in the Tokyo Metropolitan Natural Education Park. Why is this?

In fact, the records in Tokyo suggest that the plants were planted, and one theory suggests that they were brought in during the Edo period, with Hiraga Gennai being involved.

The theory that Hiraga Gennai was involved was proposed by the renowned botanist Makino Tomitaro, who suggested that when the National Institute for Nature Education was the secondary residence of the Takamatsu Domain, Hiraga Gennai, who was born in the Takamatsu Domain of Sanuki Province and was well-versed in herbal medicine, brought the plants from Sanuki (present-day Kagawa Prefecture).

Unfortunately, there is no direct evidence to support this. However, records exist that the Sanuki Takamatsu Domain transported medicinal herbs from various locations within the domain to present-day Takamatsu City in order to create a medicinal herb garden, and it has been revealed that Hiraga Gennai was involved in this transport. Therefore, although it is not confirmed, it can be said that it is a possibility.

What is the structure of the flower? How is it pollinated?

From August to November (Hagiwara, 2013), dense clusters of reddish-purple flowers bloom in short spike-like inflorescences in the leaf axils. The corolla is reddish-purple to purple, and two long stamens protrude from the flower.

Unfortunately, there is still a lack of research on this plant, and very little is known about the types of insects that visit it for pollination. However, the official website of the Botanical Garden states that "the hoverfly Episyrphus balteatus has been observed visiting the flowers several times" (Botanical Garden, 2009).

A related species is Veronicastrum japonicum, which has a similar flower structure, but the flowers are arranged in long inflorescences, making it look completely different. Various types of insects, including beetles, bees, hoverflies, and butterflies, have been confirmed to visit Veronicastrum japonicum (Tanaka, 1970; Tanaka and Hirano, 2000), but the inflorescence of Veronicastrum sibiricum is short, and it is thought that insects cannot easily spread through it, so it is possible that it does not attract as many types of insects as Veronicastrum japonicum. Alternatively, it may be able to complete pollination with a smaller number of insects.

As it is a rare species, there is still much we don't know about it, but I look forward to future research.

What is the structure of the fruit? How are the seeds dispersed?

The fruit is a flattened, oval-shaped capsule. The seeds are minute, measuring 0.5–0.7 mm in length, 0.5–0.6 mm in width, and about 0.4 mm in thickness, and are somewhat flattened, nearly circular, irregular ellipsoids (Hagiwara, 2013). The number of seeds is large, with records of 298–3,726 seeds being produced in experiments.

Although the ecology of the fruits and seeds is not yet fully understood, seed germination experiments have revealed that they exhibit strong photogermination properties and a strong dormant state.

Therefore, even in nature, it is thought to produce a large number of tiny seeds, and due to its strong dormancy, it remains in the soil as buried seeds, continuing to survive as seeds for a long period of time. The optimal relative light intensity for germination is said to be around 20%, and it will germinate if it is given moderate direct sunlight. This is likely what led to its survival in the nature education garden (Hagiwara, 2014).

References

Hagiwara, Shinsuke. 2013. Reproduction of *Platanthera japonica* in Kitakyushu Science and Research City. Report of the National Institute for Nature Education 44: 83-93. ISSN: 0385-759X, https://www.kahaku.go.jp/research/publication/meguro/download/44/ns-r-44_1-9.pdf

Hagiwara, Shinsuke. 2014. The rediscovery of *Platanthera japonica* in the Natural Education Garden attached to the National Museum of Nature and Science and the article in the 1915 issue of the "Oriental Arts and Culture Magazine". Report of the Natural Education Garden 45: 47-53. ISSN: 0385-759X, https://www.kahaku.go.jp/research/publication/meguro/download/45/ns-r-45_1-6.pdf

Nagamatsu, D., Sakata, N., & Yadagai, S. 2016. Rediscovery of *Ophioglossum sieboldii* in the Tottori Sand Dunes and new confirmation of *Platanthera japonica* and *Platanthera longifolia* in Tottori Prefecture. San'in Natural History Research 12: 22-25. ISSN: 1349-2535, https://repository.lib.tottori-u.ac.jp/records/7462

Tanaka, Hajime. 1970. Pollination of Veronicastrum sibiricum and insects. Collection and Rearing 32: 194-196. ISSN: 0036-3286

Tanaka, Hajime & Hirano, Takahisa. 2000. The Face of Flowers: Wisdom for Bearing Fruit. Yama-kei Publishers, Tokyo. 191pp. ISBN: 9784635063043

Satake, Yoshisuke. 1999. Wild Plants of Japan (New Edition, Herbaceous Plants 3, Sympetalous Plants). Heibonsha, Tokyo. 259pp. ISBN: 9784582535037

Natural Botanical Garden. July 23, 2009. Best viewing information. Affiliated Natural Education Garden website. http://www.ins.kahaku.go.jp/season/index.php?id=0001249525715772

Wildlife Research Association / Envision Environmental Conservation Office. January 5, 2021. Japan Red Data Search System. http://jpnrdb.com/index.html

Veronica persica, Veronica polifolia, Veronica undulata, and Veronica polifolia are four blue wild species found in fields and roadsides around the world. In Japan, they are representative early spring flowers, and may be among the first plants whose names you learn when you become interested in weeds. However, since all of them have blue to purple flowers and their leaves look similar at first glance, you may have trouble distinguishing them. However, you can distinguish them by carefully observing the way the stems stand and the shape of the leaves, flowers, and fruits. Although Veronica persica can now be seen all over Japan, it was actually first confirmed in Japan in the early Meiji era. Before that, another species called Veronica polifolia was found all over Japan. Now, Veronica polifolia has disappeared from roadsides and is found almost only in rocky areas and stone walls. There have been various theories as to why this is the case, but recent research strongly suggests that it is a result of Veronica persica displacing Veronica polifolia. There are various factors that could cause Veronica polifolia to be driven out, but a well-known biological phenomenon called "reproductive interference" may also be involved. While there are differences in the length of the flower stalks and the size of the flowers of the Veronica genus, this may be due to differences in their reproductive methods. Species with long flower stalks undergo cross-pollination, while those with short stalks do not. Species with long flower stalks are frequently visited by small bees and flies, which are commonly seen in early spring. The fruit is a capsule, and the seeds of some species have elaiosomes and are dispersed by ants. This article will explain the classification, history, evolution, pollination ecology, and seed dispersal of Veronica species.

Four blue wild species found in fields and roadsides around the world

Veronica persica, also known as "large dog's scrotum," is considered to be native to Europe in Japanese literature (Kanagawa Prefecture Flora Survey Association, 2018), but in Chinese literature, it is considered to be native to Southwest Asia (Wu & Raven, 1998). It has spread as a naturalized species throughout the world, and in Japan, it was first confirmed in the early Meiji era and had spread throughout the country by 1919 (Tsuruuchi, 1994). It is a biennial plant that grows in vacant lots and along roadsides (Kanagawa Prefecture Flora Survey Association, 2018).

Veronica arvensis, also known as "standing dog's scrotum," is described in Japanese literature as being native to Europe (Hayashi et al., 2013) or to Eurasia and Africa (Kanagawa Prefectural Flora Survey Association, 2018). Chinese literature describes it as being native to Southern Europe and Southwest Asia (Wu & Raven, 1998). It has expanded its distribution as a naturalized species worldwide, and in Japan, it was noticed around the middle of the Meiji era. Currently, it is distributed throughout the country (Hayashi et al., 2013) and is an annual plant that grows in vacant lots and along roadsides (Kanagawa Prefectural Flora Survey Association, 2018).

Veronica hederifolia is native to Europe and Africa (Kanagawa Prefectural Flora Survey Association, 2018) and grows in fields and roadsides. In Japan, it was first discovered in Nagasaki in 1862 during the Edo period by a British person (Tsuruuchi, 1994), and is now distributed throughout the country, growing in fields and roadsides as an annual plant (Kanagawa Prefectural Flora Survey Association, 2018).

Veronica polita subsp. lilacina, also known as dog's scrotum, is native to Southwest Asia (Wu & Raven, 1998). It likely naturalized in ancient times and grew along roadsides and in grasslands in Hokkaido, Honshu, Shikoku, Kyushu, Amami, and Okinawa prefectures (Kyoto Prefecture, 2015; Kanagawa Prefecture Flora Survey Association, 2018). However, it is thought to have been overwhelmed by Veronica persica, which was introduced later, and is now mainly found in coastal areas as a biennial plant (Kanagawa Prefecture Flora Survey Association, 2018). It is designated as Vulnerable (VU) by the Ministry of the Environment.

All of these species belong to the genus Veronica in the family Plantaginaceae and are commonly found (or were found) in fields and along roadsides. In particular, Veronica persica might be one of the first plants whose name you learn when you become interested in weeds.

There are various theories about their place of origin, but they are generally the same. The flowers are blue to purple, and the leaves look similar at first glance, so you might have trouble distinguishing them.

What are the differences between Veronica persica, Veronica polifolia, Veronica undulata, and Veronica polifolia?

We need to compare several characteristics of these four types.

First, in Veronica polita, the upper bracts gradually become smaller and differ in shape from the opposite lower leaves, whereas in Veronica persica, Veronica flavescens, and Veronica polita, the bracts are the same shape as the leaves.

However, this is a distinction based on plant taxonomy, and confirming this point may be difficult for beginners.

Another difference is that, as its name suggests, the stem of Veronica persica clearly stands vertically to the ground, its leaves are broadly ovate with entire margins or slightly large serrations, and it has almost no flower stalks, whereas the other three species creep along the ground, their leaves have prominent serrations, and they have flower stalks.

Regarding the remaining three species, the differences are that in Veronica persica and Veronica polifolia, the leaves are papery and dull, with 2 to 5 pairs of coarse serrations, and the fruit, if bi-spherical, has long white hairs on the outer surface, while in Veronica serrata, the leaves are somewhat fleshy and glossy, with 1 to 2 pairs of large serrations, and the fruit is bi-spherical with no long white hairs on the outer surface.

Regarding the remaining species, Veronica persica and Veronica polita, Veronica persica has 3 to 5 pairs of serrations on its leaves, its flowers are azure, and the ends of its fruit are slightly pointed, while Veronica polita has 2 to 3 pairs of serrations on its leaves, its flowers are pale pink, and the ends of its fruit are rounded.

In addition to the above, it may be helpful to note that *Veronica polifolia* spread from Nagasaki, resulting in its dense growth in western Kyushu, and that, as mentioned above, *Veronica polifolia* now mainly grows on stone walls in coastal areas.

In recent years, Veronica cymbalaria, which resembles Veronica flavescens, has been found in Tokyo and Kanagawa prefectures, but it can be distinguished by having more serrations (often 5 on each side) and white flowers.

Is it true that "Veronica polita was driven out by Veronica persica"?

Although Veronica persica is now a common species in Japan, as mentioned above, it was first confirmed in the early Meiji period, and it is believed that it did not exist before then. It may have arrived with the Meiji Restoration and the subsequent boom in trade. It is said that in the past, Veronica polifolia grew along roadsides instead of Veronica persica.

Because of this, it is sometimes said that "Veronica polita was driven out by Veronica persica." Is this really true?

In fact, there was disagreement among researchers on this matter (Takakura et al., 2011; Kanagawa Prefecture Plant Survey Association, 2018).

In the 1988 botanical illustration by the renowned botanist Tomitaro Makino, Veronica polita is described as "growing in fields and along roadsides." A similar description can be found in a botanical guide compiled by Kanagawa Prefecture.

However, their habitat is now limited to rocky areas and stone walls along the coast and inland.

This could be interpreted as the Japanese speedwell being driven out by the large speedwell, or it could be interpreted as the Japanese speedwell originally inhabiting rocky areas and stone walls, and its growth in fields and roadsides being a minority occurrence, suggesting that there was a natural habitat separation between the two species.

To clarify this, we would like to examine records prior to Makino's records, but when researchers investigated the specimens held at the Osaka Museum of Natural History, they found that there were almost no specimens from before World War II, and most of the specimens that were from shortly after the war were already almost entirely of Ishigaki origin.

In other words, there was no evidence anywhere to determine which side was right. This could easily become a cold case.

So, Veronica persica doesn't actually prefer rocky areas or stone walls?

However, in an attempt to uncover the truth through alternative means, researchers similar to those who investigated the museum also investigated the habitat of Veronica persica on numerous remote islands in the Seto Inland Sea, which have little human traffic and are less affected by the naturalization of Veronica persica.

As a result, it became clear that the further the island is from the mainland, the fewer Veronica persica plants there are, and the more Veronica polifolia plants become dominant along roadsides and in cultivated fields.

Furthermore, on the island where Veronica polita inhabits roadsides and cultivated fields, rocky areas and stone wall environments also exist. From this, it was inferred that Veronica polita did not originally prefer rocky areas or stone wall environments.

This research suggests that Veronica persica was indeed driven out by Veronica polifolia and relegated to rocky areas and stone wall environments.

Why were the Veronica polifolia plants wiped out?

It is said that Veronica persica has driven out Veronica polita, but there is no evidence that Veronica persica attacks Veronica polita through allelopathy or any other means, nor is there any evidence that Veronica persica is particularly more prolific than Veronica polita.

Why did this asymmetrical situation occur?

Of course, the reasons mentioned above may be involved, but another hypothesis, or one that may have accelerated the situation, is that an asymmetrical phenomenon called "reproductive interference" occurred.

Reproductive interference is a phenomenon in which the reproductive capacity of closely related species is reduced when they crossbreed. In this context, it refers to the inability to produce seeds (sterility) when the pistil of one species receives pollen from another species.

Experiments that confirmed this showed that when Veronica persica received pollen from Veronica polifolia, it reduced its seed production, but Veronica polifolia was not affected by Veronica persica (Takakura, 2013).

This difference in response when receiving pollen from different species may be one of the factors contributing to the asymmetrical distribution.

However, there seems to be a considerable time lag between 1919, when Veronica persica spread throughout Japan, and 1945, when Veronica polifolia appears to have begun to decline. It can be said that the reason for this time lag is still unknown.

What is the flowering period and flower shape of Veronica species?

Veronica persica blooms from March to May. It produces sapphire-blue flowers on pedicels 1-2 cm long from the leaf axils at the top of the stem. The flowers are 0.8-1 cm in diameter and only open when exposed to sunlight. The corolla is four-lobed, with the upper lobe being slightly larger and darker in color. It has two stamens.

Veronica polita blooms from March to May. It bears a single small blue flower in the upper leaf axil. The flower is 4 mm in diameter. It has almost no pedicel and blooms almost embedded in the bracts and calyx. The calyx has glandular hairs and short hairs.

The flowering period for *Furasaba-sou* is from April to May. From the upper leaf axils, flower stalks about the same length as the leaves emerge, bearing a single pale bluish-purple flower 3-4 mm in diameter.

Veronica polifolia blooms from February to April. It bears a single flower, about 0.5 cm in diameter, on a pedicel in the leaf axil at the top of the stem. The corolla is 4-lobed and pale reddish-purple. The calyx is also 4-lobed.

They all share the common characteristic of being blue flowers that bloom in early spring.

Are there differences in how flowers reproduce depending on their size and shape?

Do differences in flower size and shape lead to differences in how they reproduce?

Combining the results of several studies, it has been found that Veronica persica and Veronica arvensis perform both self-pollination and cross-pollination, while Veronica polifolia performs only self-pollination (Tsuruuchi, 1994; Tanaka and Hirano, 2000). It is unclear about Veronica polifolia, but it is likely that it performs at least cross-pollination.

This is also reflected in the shape of the flower.

While the flower stalks of Veronica persica, Veronica undulata, and Veronica polifolia are elongated, albeit to varying lengths, Veronica arvensis has almost no flower stalks.

Veronica persica, Veronica polifolia, and Veronica polifolia all have long flower stalks, and the flowers are supported by these long stalks. This allows insects that come to the flower to cling on to avoid being shaken off, and they pull the two stamens that grow there towards their own bodies (Tanaka and Hirano, 2000). In addition, the anthers (the part of the stamen that produces pollen) are T-shaped, which also allows them to stick tightly to the insect's body, like a vacuum cleaner or a Swiffer.

The insects that visit Veronica persica and Veronica undulata have been studied in detail, and in Japanese studies, the majority of visitors were small bees and flies, including hoverflies (Tsuruchi, 1994). Although not directly mentioned in this study, generally speaking, the only pollinating insects that can be active even at early spring temperatures are small bees and flies that are resistant to cold. It can be said that the small size of the flowers is perfectly adapted to small insects. However, there is currently no clear difference in the insects that visit Veronica persica, which has particularly large flowers, and Veronica undulata, which has small flowers.

As evening approaches, the stamens curve inward, bringing the anthers and stigmas into contact, allowing for self-pollination (Tanaka, 1976).

On the other hand, Veronica persica has almost no flower stalks, and its diameter is about 4 mm, making it less conspicuous than Veronica polifolia (Tanaka, 1976). It blooms late, around 10 am, and closes around 3 pm. A small amount of nectar is secreted, but no insects visit it, and self-pollination occurs immediately after blooming as the anthers of the stamens and the stigma of the pistil touch inside. It can be said that it is self-pollinating without the use of insects.

These differences may have some impact on breeding in the wild, but the details are not yet known.

However, Veronica persica has flowers that are particularly well adapted to insects in early spring, and its ability to self-pollinate gives it the flexibility to adapt to various environments, which is likely one of the reasons why it has spread so widely across the Eurasian continent.

What is the structure of the fruit?

The fruit is a capsule. The name "Inunofuguri" (dog's scrotum) comes from the fact that this capsule resembles a dog's scrotum.

In Veronica persica, the capsule is flat, about 4 mm long and 6-7 mm wide, with long hairs only along the edges. Inside are boat-shaped seeds.

In Veronica polita, the capsule is flat, about 3 mm long and 4 mm wide, with glandular hairs along the edge. Inside are flattened, oval-shaped seeds.

In *Furasaba-sou*, the capsule is nearly spherical, 2.5-3 mm long, with a slightly indented tip. It contains 1-3 seeds and is deeply boat-shaped.

In Veronica polita, the capsule is somewhat flattened, round, and has white hairs on its surface, mixed with glandular hairs. The seeds are about 1.5 mm long.

Some species of seeds are dispersed by ants, while others are not!?

Are there any differences in the ecology of these fruits as well?

According to research conducted at Kyoto University, both Veronica persica and Veronica polita have elaiosomes attached to their seeds, which serve as food for ants. When the seeds mature, they split open, exposing the seeds, which then fall to the ground and are dispersed by ants (Miura et al., 2003).

Specifically, in the case of Veronica polita, the ants *Pheidole megacephala*, *Lasius nigricans*, and *Lasius niger* were responsible for transporting the seeds. The behavior of *Veronica persica* has not been clarified.

On the other hand, Veronica polita does not have elaiosomes, and although not explicitly stated in the paper, it is likely that it is dispersed by gravity or wind.

While it's unclear how these differences in seed dispersal affect reproduction in the wild, the fact that Pheidole megacephala, Lasius niger, and Lasius niger are all species found in fields and urban areas, and considering seed dispersal in addition to flowers, it becomes clear why they are found in such locations.

The speedwell plant has evolved to prevent its seeds from falling off cliffs!?

More detailed information is available regarding seed dispersal in Veronica polita (Takakura et al., 2011).

As mentioned above, Veronica persica was driven out by Veronica longifolia and forced to live in rocky areas and on stone walls.

However, evolution also occurred in order to adapt to the environment.

Normally, when the seeds of Veronica persica mature, they split open wide, exposing the seeds, which then fall to the ground. However, in environments such as rocky areas or stone walls, the seeds fall all the way down and cannot return to their habitat.

Therefore, Veronica polita, which grows in rocky areas and stone walls, has adapted its fruit so that after the seeds are exposed, they split open upwards, leaving only the seeds exposed within the fruit.

This method allows ants to carry the seeds directly from the fruit and freely disperse them within rocky areas and stone walls.

This indicates that Veronica polita is not simply being pushed to rocky areas and stone walls, but is undergoing a high level of adaptation.

References

Hayashi, Yasaka, Kadota, Yuichi, and Hirano, Takahisa. 2013. Yamakei Handy Illustrated Guide 1: Wildflowers (Revised and Expanded New Edition). Yama-kei Publishers, Tokyo. 664pp. ISBN: 9784635070195

Miura, Reiichi, Noriko Doi, and Masahiro Yoshino. 2003. Distribution of Veronica polita around Kyoto University and seed dispersal by ants. Weed Research 48(3): 140-142. https://doi.org/10.3719/weed.48.140

Takakura, Koichi. 2011. Polymorphism in Veronica polita: Adaptation to stone wall environments and relationship with seed dispersers. Bulletin of the Kanto Branch of the Ecological Society of Japan 59: 19-25. ISSN: 0289-2421, https://esj.ne.jp/kanto/bulletin/no.59.pdf#page=20

Takakura, K. 2013. Two-way but asymmetrical reproductive interference between an invasive Veronica species and a native congener. American Journal of Plant Sciences 4(3): 535-542. https://doi.org/10.4236/ajps.2013.43069

Kanagawa Prefecture Flora Survey Association. 2018. Kanagawa Prefecture Flora 2018 (Electronic Edition). Kanagawa Prefecture Flora Survey Association, Odawara. 1803pp. ISBN: 9784991053726

Tsurunai, Takayuki. 1994. Reproductive ecology of Veronica persica and Veronica polifolia. Weed Research 39(2): 85-90. ISSN: 0372-798X, https://doi.org/10.3719/weed.39.85

Tanaka, Hajime. 1976. Observation of insect-pollinated and wind-pollinated flowers. New Science Co., Ltd., Tokyo. 109pp. ISBN: 9784821600236

Tanaka, Hajime & Hirano, Takahisa. 2000. The Face of Flowers: Wisdom for Bearing Fruit. Yama-kei Publishers, Tokyo. 191pp. ISBN: 9784635063043

Wu, ZY & Raven, PH (Eds.). 1998. Flora of China (Vol. 18 Scrophulariaceae through Gesneriaceae). Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis. 450pp. ISBN: 9780915279555

Digitalis (foxglove) and comfrey are two horticultural species native to Europe that are known to be poisonous. Their leaves are very similar, with the upper leaves lacking petioles and the base having petioles, and they also have wings (where the leaf blade extends onto the stem). There were cases in the past where people mistakenly ate digitalis, mistaking it for comfrey, which was once edible. The two species are completely different in terms of classification, and their flowers and fruits are entirely different. Although their leaves are similar, they can be properly distinguished by checking the serrations and the appearance of the bristles. Digitalis poisoning has been known for a long time, and there have been many cases of death, but it is also important for its medicinal uses and is used for congestive heart failure. Comfrey was once lauded as a versatile longevity vegetable and was edible, but after cases of liver damage were confirmed, its use has fallen out of favor and it has become disliked. Digitalis flowers are large and suitable for ornamental purposes, but in Europe they originally evolved to attract bumblebees. However, recent research has shown that wild populations in South America have evolved to adapt to hummingbirds, which are native pollinators of the Americas. Comfrey flowers also heavily rely on bumblebees for pollination, but the rate of successful cross-pollination is low. It has been found that bumblebees with sharp mouths that steal nectar cause the corolla to fall off, increasing self-pollination, giving it a unique ecological characteristic. This article will explain the classification, toxicity, pollination ecology, and seed dispersal of digitalis and comfrey.

Two toxic horticultural species native to Europe

Digitalis purpurea, commonly known as foxglove or foxglove, is a perennial herb native to Europe, where it grows in mountainous regions (Izawa, 1980). It belongs to the Plantaginaceae family. It has also naturalized in temperate regions and tropical highlands (Mackin et al., 2021). In Japan, it was introduced during the Edo period and cultivated for ornamental purposes (Izawa, 1998), but some have naturalized. It is also known for its extremely high toxicity (Izawa, 1980).

Comfrey (Symphytum x uplandicum) is also known as Russian comfrey. Native to Europe, it is a hybrid of Symphytum asperum and Symphytum officinale. It is a perennial plant belonging to the Boraginaceae family. It has become widely naturalized in North America and New Zealand, and in Japan, it was introduced and cultivated as an ornamental plant in 1958, and has since naturalized in vacant lots in populated areas and urban areas.

Both of these species are native to Europe and are used in horticulture. Their leaves are very similar, with the upper leaves lacking petioles and the base having petioles, and they also have wings (where the leaf blade extends onto the stem). While digitalis is highly poisonous, comfrey was once eaten in Japan, and there are known cases both domestically and internationally of people mistakenly eating digitalis after mistaking it for comfrey (Ministry of Health, Labour and Welfare, 2023).

What is the difference between digitalis and comfrey?

However, there are many differences between digitalis and comfrey.

First of all, in terms of classification, digitalis belongs to the Plantaginaceae family, while comfrey belongs to the Boraginaceae family, so they are fundamentally different species.

The flowers and fruits are completely different.

In foxglove, numerous flowers bloom in long racemes at the top of the stem, with a simple bell-shaped corolla that is 3-4.5 cm long and reddish-purple. In contrast, in comfrey, 10-20 flowers are clustered in a spiral cymose at the top of the stem, with a bell-shaped corolla that is 1.4-1.5 cm long, pale purple to purplish-red to yellowish-white, shallowly 5-lobed at the tip, and the lobes are triangular and revolute.

Regarding the fruit, digitalis produces capsules that are about 15 mm long and broadly ovate, while comfrey usually does not produce fruit, but if it does, it is a small nutlet that schizocarps into four parts, is 3-4 mm long, black, smooth, glossy, and grows inside the calyx.

However, the problem arises when the flowers are not in bloom. It's not ideal to judge at this time, but there are differences even just in the leaves and stems.

While foxglove has short, grayish-white hairs on its stems and inconspicuous leaf hairs, comfrey has distinctly long, bristly hairs all over its body, including numerous bristles on its leaves. Comfrey can be painful if you touch it carelessly, as the hairs can prick you.

Furthermore, while foxglove leaves have serrated edges, comfrey leaves are entire and lack serrations.

When distinguishing between the two types, be sure to check the above items.

It should be noted that comfrey is often confused with Symphytum officinale and Symphytum pedunculosa, and even the Japanese Wikipedia entry confuses them, but they are different species. Symphytum pedunculosa has winged stems with short, downward-pointing hairs, while Symphytum officinale has wingless stems with spine-like hairs. Comfrey, on the other hand, has winged stems with spine-like hairs.

What is "digitalis poisoning," a condition known for a long time?

Digitalis is poisonous throughout the entire plant, and "digitalis poisoning" has been known for a long time. Symptoms include cardiovascular symptoms such as arrhythmias and palpitations, gastrointestinal symptoms such as nausea and vomiting, neurological symptoms such as headaches and dizziness, and a yellowish tint to the field of vision (xanthopsia). The mechanism is that it inhibits Na ⁺ /K ^{+ -ATPase} in the cell membrane, increasing the concentration of Na ⁺ and Ca2 ⁺ in the cell and enhancing the contractility of ^the myocardium.

Deaths are rare, but in the United States, 2,500 cases were reported in 2011, with 27 deaths recorded (Palatnick, & Jelic, 2020).

On the other hand, it is also used medicinally because it enhances the contractility of the heart muscle. Digitoxin, a cardiac glycoside, was extracted from hot-air dried digitalis leaves, but today it is chemically synthesized. It has been used as medicine for cuts and bruises since ancient times. In 1776, William Withering of England published his findings on its medicinal properties as a cardiac stimulant.

Digitoxin is not naturally present in plants but is a component secondarily produced through enzymatic degradation. Digitalis contains cardiac glycosides, as well as pregnane glycosides such as diginine, steroid saponins, and flavonoids. Digitoxin is used as a treatment for congestive heart failure, but it is not widely used clinically because its absorption rate from the gastrointestinal tract is almost 100%.

Digoxin and lanatoside C, used in the prevention and treatment of chronic heart failure along with digitoxin, are not found in digitalis, but are enzymatically broken down from components of the related plant, Digitalis lanata. This point is also sometimes confused.

However, the use of these medications is said to be decreasing due to advances in research on new drugs and an increase in reports of adverse events from their combined use with macrolide antibiotics and antifungal agents.

While it's a beautiful plant for ornamental purposes, please be extremely careful not to ingest it.

Comfrey was once considered nutritious, but now it's disliked due to its toxicity...?

Comfrey was once considered a versatile vegetable that promotes longevity.

The roots and rhizomes contain alkaloids such as consolidine and symphytosinoglycin, as well as mucilage and tannins. Tannins have astringent properties and were historically used orally as an antidiarrheal, or as a poultice for eczema and rashes. Fresh leaves contain 901 TP3T of water, approximately 2.41 TP3T of crude protein, and approximately 0.2% of crude fat. Trace elements include minerals and vitamins (vitamin A, vitamin _B1, vitamin _B2, vitamin C, vitamin _B3, vitamin _B5, vitamin _B6, and vitamin _B12), and it has been widely used for medicinal and culinary purposes.

In Europe and America, the rhizome was primarily used externally. In Japan, the leaves were used as a tonic food, and the raw leaves were used to make green juice or prepared in dishes such as tempura, blanched greens, and salads. The roots were touted for their beauty benefits and were used as a bath additive.

However, on June 14, 2004, the Ministry of Health, Labour and Welfare issued a warning against consuming comfrey, citing numerous cases reported overseas of liver damage (hepatic veno-occlusive disease, mainly cirrhosis or liver failure and liver cancer due to non-thrombotic occlusion of the hepatic venules) resulting from the consumption of comfrey. On June 18, 2004, the ministry also banned the sale of comfrey as a food product.

Even though it's consumed in so many places, it doesn't seem to cause hospitalizations, suggesting that comfrey is far less toxic than digitalis. However, considering the long-term effects of ingestion and the situation overseas, the ban on its sale can be seen as a preventative measure.

These symptoms are caused by the pyrrolizidine alkaloids etimidine and symphytine, which are found in the roots at the highest concentrations. It is thought that the alkaloids are converted into their original form by cytochrome P450, and in addition to being acutely toxic, there have been reports of effects on the fetus through the placenta.

Thus, the use of comfrey fell out of favor. As a result, it became unpopular because it can sting when it pricks you, it can grow wild, and it is known to inhibit the growth of other plants due to the allelopathic substance rosemary acid.

However, some researchers have expressed the opinion that "comfrey contains components toxic to the human body, but bracken, a traditional Japanese food ingredient, also contains powerful carcinogens. However, bracken becomes non-toxic when prepared using traditional methods to remove the bitterness, so its consumption is not prohibited. Comfrey is rich in vitamins and minerals and is highly nutritious. If harmful components are removed through devising cooking methods, it is a useful plant with high nutritional value. It would be a shame to simply abandon a plant with a history of being eaten" (Fujii, 2008).

If a suitable cooking method is discovered in the future, it may once again attract attention.

Did digitalis evolve from being pollinated by bumblebees to being pollinated by hummingbirds in America?!

Digitalis flowers from June to July, bearing numerous downward-facing flowers in long racemes at the top of the stem. The corolla is 3-4.5 cm long, reddish-purple, and simply bell-shaped, with dark markings on the underside of the interior and covered in long hairs. The two stamens are located on the upper side of the corolla. The calyx is deeply five-lobed. The reddish-purple markings are conspicuous and are thought to attract insects as nectar guides.

What kinds of insects visit flowers with such large openings?

Studies in its native Britain and Norway have shown that bumblebees with long tongues are the ones that visit the area.

This large entrance is quite large and is thought to have evolved to accommodate large bees such as bumblebees.

Surprisingly, however, research has shown that the foxglove populations introduced for cultivation in Colombia in South America and Costa Rica in Central America, and subsequently naturalized, have undergone a certain evolutionary process (Mackin et al., 2021).

In the 1850s, feral foxglove populations began to be visited more frequently by hummingbirds, which are not native to their native habitat, than by bumblebees.

This hummingbird is much more capable of carrying pollen than the bumblebee. However, the hummingbird's beak is too large to properly insert its beak into the nectar-filling opening at the back of the petal, called the "proximal corolla tube," which is adapted to the bumblebee, and thus it does not favor this flower.

In such situations, individuals of foxglove with a larger proximal corolla tube were more likely to be pollinated than those with a smaller one, giving them an advantage in seed production. As a result, the Colombian population in South America and the Costa Rican population in Central America consisted almost entirely of individuals with large proximal corolla tubes, evolving to be more easily pollinated by hummingbirds. This can be described as a remarkable example of adaptability.

This evolutionary shift in pollinators isn't limited to foxgloves; it's seen in the flowers of many other plants as well. It's thought that it all started with small changes like these.

Comfrey flowers were being pollinated thanks to "nectar thieves"!?

Comfrey flowers from June to August. The flowers are clustered in a spiral cymose inflorescence at the top of the stem, with 10 to 20 flowers per cluster. The corolla is 1.4 to 1.5 cm long, pale purple to purplish-red to yellowish-white, bell-shaped, and shallowly 5-lobed at the tip. The lobes are triangular and spiral outwards. The filaments are about 3 mm long, and the anthers are about 3.5 mm long.

What kinds of insects visit bell-shaped flowers?

In an experiment using comfrey, a study conducted in China observed flowers for 50 hours, recording a total of 2,539 visits and 14 species of insects (Hou et al., 2021). These included 8 species of bumblebees, 2 species of other bees, and 4 species of butterflies.

However, only three species of bumblebee— Bombus hedini, Bombus ladakhensis, and Bombus kashmirensis —entered through the bell-shaped entrance and properly touched the stamens and pistils. The remaining 91.7% were "nectar robberies," inserting their long, sharp mouthparts from the side of the corolla and stealing only the nectar.

Common sense would suggest that only these three species promote cross-pollination and contribute to seed production, while all other insects are considered a nuisance to flowers.

However, the interesting part is this: when we attached sticky tape to the sides of the corolla to prevent nectar theft, the fruit set rate decreased.

In other words, for some reason, the presence of nectar thieves allowed the comfrey flowers to be pollinated, increasing their fruit-setting rate. Why is this?

The reason for this has been revealed in the same study.

In comfrey flowers, the pistil is firmly attached to the calyx at its base, while the stamens are attached to the corolla. The style of the pistil is very long, and the stamens are noticeably shorter. Also, comfrey is self-compatible (it can be pollinated with its own pollen).

It has been observed that when a nectar thief grabs the corolla from the side and inserts its mouth, the corolla is highly likely to slip down and eventually fall off. When it slips down, the anthers of the stamens attached to the corolla come into contact with the stigma of the pistil.

In other words, comfrey relies on nectar robbing to promote self-pollination. This is an unusual phenomenon not seen in other species and is a fascinating aspect of its ecosystem.

On the other hand, self-pollination was originally intended to reduce the effort required for cross-pollination, such as using insects, and to allow for more efficient reproduction. Why insects came to be used even for self-pollination remains unclear. However, there may be some rationality to it in the sense that it allows for both self-pollination and cross-pollination to coexist.

Digitalis fruits are capsules, while comfrey fruits are small nuts.

The fruit of the foxglove is a capsule, about 15 mm long and broadly ovate. The seeds are numerous, oblong to subovate, small, and ridged.

It is known that the tiny seeds mature within a month after flowering, and are dispersed by gravity or wind from the capsule (Sletvold & Rydgren, 2007). Most seeds fall within a few meters of the mother plant and germinate the following spring, or they are stored in the soil as a "seed bank" and germinate when environmental conditions are right.

Comfrey, on the other hand, does not usually bear fruit, but when it does, it produces small nutlets that are schizocarps, divided into four parts, 3-4 mm in size, black, smooth and glossy, and grow inside the calyx. The attachment scar is at the base and is dome-shaped with fine teeth on the edge. The dome has a white "elaiosome" derived from the pericarp (Mayer et al., 2005). Since the pericarp remains attached to the seed, what appears to be a "seed" is actually the "fruit".

In Symphytum officinale, which has been well studied in Europe, it has been found that the seeds are "dispersed by ants" who come seeking elaiosomes, a food source attached to the fallen fruits (Peters et al., 2003; Lengyel et al., 2010; Englický & Šera, 2018).

References

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Hou, QZ, Ehmet, N., Chen, DW, Wang, TH, Xu, YF, Ma, J., & Sun, K. 2021. Corolla Abscission Triggered by Nectar Robbers Positively Affects Reproduction by Enhancing Self-Pollination in Symphytum officinale (Boraginaceae). Biology 10(9): 903. ISSN: 2079-7737, https://doi.org/10.3390/biology10090903

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Mackin, CR, Peña, JF, Blanco, MA, Balfour, NJ, & Castellanos, MC 2021. Rapid evolution of a floral trait following acquisition of novel pollinators. Journal of Ecology 109(5): 2234-2246. ISSN: 0022-0477, https://doi.org/10.1111/1365-2745.13636

Mayer, V., Ölzant, S., & Fischer, RC 2005. Myrmecochorous seed dispersal in temperate regions. In PM Forget, JE Lambert, PE Hulme, & SB Vander Wall (Eds.), Seed fate: predation, dispersal and seedling establishment (pp. 175-195). CABI Publishing. ISBN: 9780851998060

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Source

This article is a significantly expanded version of a piece originally published in the following book.