Japanese Andromeda (Pieris japonica), Ryukyu Andromeda (Pieris ryukyuensis), and Japanese Andromeda (Lyonia ovalifolia) all belong to the Ericaceae family, have downward-facing, urn-shaped to bell-shaped flowers, and their bark can be twisted. They also all share the characteristic of being poisonous. Therefore, some people may have difficulty distinguishing them. However, Japanese Andromeda and Ryukyu Andromeda belong to the genus Pieris, while Japanese Andromeda belongs to the genus Lyonia, and they differ significantly in leaf shape, arrangement, and fruit shape. Japanese Andromeda and Ryukyu Andromeda differ in leaf margins and flowers. Several other varieties and cultivars of Japanese Andromeda are also known. This article will explain the classification and morphology of the genera Pieris and Lyonia.

What are Pieris japonica, Pieris ryukyuensis, and Pieris japonica?

Pieris japonica subsp. japonica, also known as Japanese Andromeda, is distributed throughout Honshu (south of Miyagi Prefecture, Kanto region, Pacific coast of Chubu region, Kinki region, Chugoku region), Shikoku, and Kyushu in Japan. It is an evergreen shrub to small tree that grows in sunny locations (Kanagawa Prefecture Flora Survey Association, 2018). It is cultivated for ornamental purposes in parks, gardens, and streets.

Pieris japonica subsp. koidzumiana, also known as Ryukyu japonica, is an evergreen shrub that was distributed on Okinawa Island but is now considered extinct in the wild due to collection for horticultural purposes. Currently, only cultivated specimens exist, and it is listed as Critically Endangered (CR) in the Ministry of the Environment's Red List 2020, and Extinct in the Wild (EW) in the Revised Okinawa Red Data Book, 3rd Edition - Fungi and Plants.

Lyonia ovalifolia var. elliptica, also known as Nejiki, is a deciduous shrub to small tree distributed in Honshu (south of Yamagata and Iwate prefectures), Shikoku, and Kyushu in Japan, growing on dry ridges and slopes in hills and mountains.

All of these plants belong to the Ericaceae family, and in addition to having downward-facing, urn-shaped to bell-shaped flowers, which are common in the Ericaceae family, they are also characterized by being woody plants, having large leaves, superior ovaries, capsule fruits, persistent or slightly persistent bracts and bracteoles, and having small, numerous seeds.

Furthermore, the bark of larger specimens can have a twisted appearance, which is the origin of its Japanese name, Nejiki, and the Japanese Andromeda (Pieris japonica) also has the same characteristic.

However, they may be better known for being poisonous plants than for their morphological features. Both Pieris japonica and Lysimachia japonica contain grayanotoxins and other toxic components, causing symptoms of poisoning such as low blood pressure, abdominal pain, diarrhea, vomiting, respiratory paralysis, and nerve paralysis (Satake, 2012). One theory is that Pieris japonica is written with the kanji characters for "horse-intoxicating tree" because horses eat its leaves and become limp, appearing as if they are drunk (Utsumi et al., 2008). In the wild, both are known to be unpalatable plants for Japanese deer, and they do not eat them (Kamaya, 1988).

However, some people may not be able to distinguish between these three types.

What are the differences between Pieris japonica, Pieris ryukyuensis, and Pieris japonica?

As a fundamental point of classification, Pieris japonica and Pieris ryukyuensis belong to the genus Pieris, while Stewartia pseudocamellia belongs to the genus Stewartia. Therefore, there are significant morphological differences between them (Kanagawa Prefectural Flora Survey Association, 2018).

Morphologically, the main difference is that Pieris japonica and Pieris ryukyuensis are evergreen (they retain their leaves throughout the winter), while Pieris japonica is deciduous (its leaves fall during the winter).

Therefore, while the leaves of Pieris japonica and Pieris ryukyuensis are hard and glossy, the leaves of Pieris japonica are soft and not glossy.

Regarding leaf arrangement, while both Pieris japonica and Pieris ryukyuensis have alternate leaves, they appear whorled because the leaves are bundled at the ends of the branches, whereas Nejiki does not have this characteristic and has the more common alternate leaf arrangement.

Regarding the leaves, even considering other subtle shapes, it's safe to say that Pieris japonica and Lysimachia japonica are completely dissimilar.

Regarding the fruit, there are differences between Pieris japonica and Pieris ryukyuensis, where the edges of the capsule lobes are not swollen and the anthers have two projections, and between Lysimachia japonica, where the capsule lobes are swollen, the anthers have no projections, and the filaments have two small projections at the end.

What is the difference between Japanese Andromeda and Ryukyu Andromeda?

While the Ryukyu pieris is now extinct in the wild and cannot be seen, seedlings are sold in gardens, so there may be situations where it's necessary to distinguish it from the common pieris.

The two varieties can be distinguished as follows (Hatsushima, 1969).

Regarding the leaves, Pieris japonica has broad leaves, with the bottom 1/3 to 1/4 of the leaf margin being entire and the rest mostly serrated, whereas Pieris ryukyuensis has narrow, slender leaves, with the leaf margin mostly entire and only 3 to 5 serrations near the top.

In short, you can consider the margins of the leaves of the Ryukyu jasmine to be almost entire (without serrations).

Regarding the corolla of the flower, there is a difference in that the corolla of Pieris japonica is urn-shaped (tapering towards the end), while that of Pieris ryukyuensis is closer to a bell-shaped (cylindrical) form.

These characteristics of *Pieris ryukyuensis* are thought to be adaptations originally for its habitat in mountain streams (Setoguchi et al., 2006).

It may be too late, but to avoid similar extinctions in the wild, let's stop collecting rare wildlife solely for our own enjoyment. Let's enjoy gardening in a sustainable way.

Are there any other similar types?

Several varieties and cultivars of Pieris japonica are known.

Pieris japonica subsp. japonica var. yakushimensis is a variety found only on Yakushima Island, characterized by its upright flowers.

Pieris japonica f. rosea is a variety with red tips on its corolla.

Pieris japonica f. elegantissima is a variety with variegated leaves.

References

Hatsushima, Sumihiko. 1969. On Japanese and Taiwanese Pieris japonica. Plants of Hokuriku 17(3): 75-76. ISSN: 0374-8081.
http://hdl.handle.net/2297/45192

Kamaya, Hajime. 1988. Changes in understory vegetation of evergreen broad-leaved forests and the effects of grazing by Japanese deer in Arakashizawa, Chiba Experimental Forest, University of Tokyo. Bulletin of the University of Tokyo Faculty of Agriculture Experimental Forest 78: 67-82. ISSN: 0371-6007, http://hdl.handle.net/2261/23128

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

Osada, N., & Sugiura, S. 2006. Effects of pollinators and flower bud herbivores on reproductive success of two ericaceous woody species differenting in flowering season. Canadian Journal of Botany 84(1): 112-119. https://doi.org/10.1139/b05-163

Osada, N., Sugiura, S., Kawamura, K., Cho, M., & Takeda, H. 2003. Community-level flowering phenology and fruit set: comparative study of 25 woody species in a secondary forest in Japan. Ecological Research 18: 711-723. https://doi.org/10.1111/j.1440-1703.2003.00590.x

Satake, Motoyoshi. 2012. Poisonous Plants of Japan. Gakken Plus, Tokyo. 232pp. ISBN: 9784054052697

Setoguchi, H., Jujita, D., Kurata, K., Maeda, Y., & Peng, CI 2006. Comparison of leaf and floral morphology among insular endemics of Pieris (Ericaceae) on the Ryukyu Islands and Taiwan. Acta Phytotaxonomica et Geobotanica 57(2): 173-182. https://doi.org/10.18942/apg.KJ00004622861

Utsumi, Y., Murata, I., Shiiba, K., and Inoue, S. 2008. Traditional names and uses of plants in the Okawachi settlement, Shiiba Village, Miyazaki Prefecture: II. Shrubs. Reports of the Kyushu University Faculty of Agriculture Experimental Forest 89: 51-62. https://doi.org/10.15017/15057

Yumoto, T. 1988. Pollination systems in the cool temperate mixed coniferous and broad-leaved forest zone of Yakushima Island. Ecological Research 3(2): 117-129. https://doi.org/10.1007/BF02346934

Enkianthus perulatus, Enkianthus campanulatus, and Rhododendron molle all belong to the genus Enkianthus in the family Ericaceae. Enkianthus perulatus and Enkianthus campanulatus are especially commonly seen cultivated as garden trees and park trees. They are known for their charming downward-facing, urn-shaped flowers. However, their leaf shapes are very similar, which can make them difficult to distinguish. To differentiate them, you need to carefully observe the size of the leaves and the amount of hairiness. They are relatively easy to distinguish when in bloom. This article will explain the classification and morphology of the genus Enkianthus.

What are Enkianthus perulatus, Enkianthus campanulatus, and Rhododendron molle?

Enkianthus perulatus, also known as the "lighthouse azalea" or "starry sky azalea," is a deciduous shrub distributed from southern Kanto to Kyushu in Japan, as well as eastern China and Taiwan. It rarely grows on rocky areas in hills and low mountains. In Japan, it is commonly cultivated as a garden tree, hedge, and park tree. The Japanese name "Dōdan" is believed to be a corruption of "Tōdai" (lighthouse), and is thought to originate from the fact that the way its branches branch into three resembles the three-legged "musubi tōdai" (tied lighthouse) used in the imperial court of ancient Japan.

Enkianthus campanulatus, also known as Sarasa-dodan or Fuurin-tsutsuji, is a deciduous shrub to small tree distributed from western Hokkaido to Kyushu in Japan, commonly growing on ridges and rocky areas in high-altitude mountainous regions. In Japan, it is commonly cultivated as a garden tree and park tree in colder regions.

Enkianthus subsessilis, also known as Abura-doudan-tsutsuji or Abura-doudan, is a deciduous shrub distributed in the Tohoku and eastern Chubu regions of Japan, growing somewhat rarely on rocky areas in mountainous regions.

All of these species belong to the genus Enkianthus in the family Ericaceae, and you'll often see Enkianthus perulatus and Enkianthus campanulatus cultivated as garden trees and park trees in many places.

Like the Pieris and Lyonia genera within the Ericaceae family, it is a woody plant characterized by its downward-facing, urn-shaped flowers. During its flowering season in spring (April-May), you can observe many of these "urn-shaped" flowers hanging downwards. Its autumn foliage is also vibrant, so you can enjoy it twice.

They also share the characteristics of having leaves that grow in clusters, are obovate in shape, and have serrated edges.

Therefore, you might sometimes get confused about the difference. Sarasa-doudan is sometimes sold as "Doudan-tsutsuji" in garden centers.

What are the differences between Enkianthus perulatus, Enkianthus campanulatus, and Rhododendron molle?

However, although the three species belong to the same genus, differences can be observed in both their leaves and flowers (Hayashi, 2019).

First, regarding the leaves, the differences are that the leaf blades of Enkianthus perulatus and Rhododendron molle are small, 2-4 cm long, the lateral veins are not prominent, and there are almost no brown, curly hairs at the branching point of the main vein and lateral veins on the underside of the leaf. In contrast, Enkianthus campanulatus has larger leaf blades, 3-7 cm long, the lateral veins are prominent, and there are brown, curly hairs on the underside of the leaf.

Enkianthus campanulatus is exceptionally large, even among the Enkianthus genus. Its growth pattern is also unique; it grows quite large, sometimes developing a thick trunk, even as it becomes a small tree.

Furthermore, only the flowers of the Enkianthus campanulatus have red tips on their corollas. The Japanese name "Sarasa-dodan" comes from the fact that the flower's pattern resembles the pattern of sarasa dyeing.

Since the leaves of Enkianthus perulatus and Rhododendron molle are quite similar, it may be a little difficult to distinguish between them.

However, there is a difference in that Enkianthus perulatus has hairless petioles and generally few hairs on the underside of the leaves, with only soft hairs at the base along the main vein, whereas Rhododendron molle has hairy petioles with brown, curly hairs, and the underside of the leaves is generally hairier, especially along the main vein.

Regarding the flowers, the corolla of the Enkianthus perulatus is long and slender, while the corolla of the Rhododendron molle is shorter and rounder, truly resembling a "vase."

Are there any other similar species?

Among the Enkianthus perulatus species, there is a known variety called Enkianthus perulatus f. japonicus, which has broad leaves.

Several varieties and cultivars of Enkianthus campanulatus are known. Benisarasadoudan var. palibinii is distributed in the highlands of northern Honshu and is a variety with entirely deep red flowers. Tsukushidoudan var. longilobus is a variety with deep flower color and deeply lobed corollas, and Kibanafuurintsutsuji f. lutescens is a variety with yellow flowers.

There are 16 other species in the Enkianthus genus distributed in Japan, so there are even more species that are difficult to distinguish. Here, we will briefly introduce some similar species.

Enkianthus cernuus f. rubens is quite similar to Enkianthus perulatus, but its petioles are shorter, the serrations are more pronounced, and the corolla is bell-shaped rather than tapering at the tip. As the name suggests, the corolla is red, but there is also a white variety called Enkianthus cernuus f. cernuus.

Enkianthus nudipes closely resembles Rhododendron molle, but its leaves are smaller, and the underside of the leaves, petioles, young branches, and inflorescences are usually hairless. It grows in rocky areas from the Chubu region to the Kinki and Shikoku regions of Japan.

References

Hayashi, Masayuki. 2019. Tree Leaves: Expanded and Revised Edition - Identifying 1300 Species Through Real-Life Scans. Yama-kei Publishers, Tokyo. 824pp. ISBN: 9784635070447

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

Hirado azalea, Kurume azalea, and Satsuki azalea (Satsuki azalea) all belong to the genus Rhododendron in the family Ericaceae, and are three species of azalea that are extremely commonly cultivated even in urban areas. However, since the shape of their flowers is almost the same, some people may not be able to distinguish between them. It is more accurate to distinguish the three species by the shape of their leaves. It is safe to say that these three species are the ones that are generally cultivated on a large scale, but due to the creation of many horticultural hybrids and varieties, there are also species that are difficult to distinguish, such as Oomurasaki azalea and Kirishima azalea. This article will explain the classification and morphology of the Rhododendron genus that are commonly cultivated in cities.

What are Hirado azalea, Kurume azalea, and Satsuki azalea?

Hirado azalea (Rhododendron x pulchrum) is a semi-evergreen shrub and a group of horticultural varieties resulting from the hybridization of several Rhododendron species (Hayashi, 2019). It is believed to have originated from hybrids of species such as Kerama azalea (R. scabrum), Taiwanese mountain azalea (R. simsii), Mochi azalea (R. macrosepalum), and Kishi azalea (R. ripense). It is commonly cultivated as an ornamental or landscaping plant in gardens, hedges, streets, and parks.

Kurume azalea (Rhododendron x obtusum 'Sakamotoi') is a semi-evergreen shrub and a group of horticultural varieties resulting from the hybridization of several Rhododendron species. It is believed to have originated from hybrids such as Kirishima azalea (Rhododendron x obtusum), a hybrid of Miyama kiusianum (Rhododendron kiusianum) and Yama azalea (Rhododendron sataense), and Sata azalea (Rhododendron sataense), which is native to Kagoshima. It is a group of horticultural varieties of hybrids.

Satsuki (Rhododendron indicum), also known as Satsuki azalea, is a semi-evergreen shrub that grows on riverbanks and rocks in southern Fukushima Prefecture, southwestern Kanto region, Kinki region, Yamaguchi Prefecture, and Kyushu (Saga Prefecture, Kumamoto Prefecture, and Yakushima) in Japan (Kanagawa Prefecture Flora Survey Association, 2018). In the wild, it inhabits a very limited environment, "rock crevices 0.5 to 4 meters above the normal water level in places that are not affected by flowing water under normal conditions but are flooded during floods," and is therefore listed on the red lists of some prefectures. However, in cultivation, it is commonly found as a garden tree, hedge, park tree, street tree, and potted plant.

All three species belong to the genus Rhododendron in the family Ericaceae, and are among the most commonly cultivated species in urban areas. They are particularly favored as street trees due to their resistance to air pollution, and are often seen planted over long distances in the "green belts" between sidewalks and roadways. Many people may have fond memories of playing with them, sucking the nectar from their flowers, when they were in elementary school.

However, since most members of the Rhododendron genus have similar flower shapes and a wide variety of flower colors, it's often difficult to distinguish them if you only focus on the flowers.

What are the differences between Hirado azalea, Kurume azalea, and Satsuki azalea?

The genus Rhododendron is an extremely vast group, with 62 species native to Japan alone, and the number is even larger when subspecies, varieties, cultivars, and hybrids created through horticulture are included.

Therefore, accurate identification can be difficult, but this time we will focus on three species that are common in urban areas.

The difference lies in the leaves (Hayashi, 2019).

First, Hirado azaleas have leaves that are covered in long hairs, are sticky when young, and have large leaf blades measuring 4-11 cm in length with many wrinkles. In contrast, Kurume azaleas and Satsuki azaleas have leaves that are covered in short yellow hairs, are not sticky even when young, have small leaf blades measuring 4 cm or less in length, and have fewer wrinkles.

The stickiness of Hirado azalea leaves is likely related to the fact that one of its parent species, Rhododendron macrosepalum, produces mucus. Considering this point, it should be relatively easy to distinguish between the two. Another characteristic is that dirt often adheres to its leaves due to the stickiness. Even mature leaves of Rhododendron macrosepalum produce a lot of mucus.

Regarding Kurume azaleas and Satsuki azaleas, the difference is that Kurume azaleas have oval-shaped leaves that are wide, while Satsuki azaleas have oblong leaves that are narrow.

Also, it's worth noting that while Kurume azaleas bloom from April to May, Satsuki azaleas bloom a little later, from May to June. The original Satsuki azalea flowers are bright pink, but they are often other colors.

Note that the shape of the leaves changes between spring and summer in the Rhododendron genus, so features such as the sharpness of the leaf tips may not be very helpful as a reference.

Are there any other similar species?

As mentioned above, the genus Rhododendron includes many species, but other species are not cultivated, or have large leaves or trifoliate compound leaves, making identification relatively easy.

However, because horticultural hybrids are created in large quantities, accurate methods for distinguishing them may not always be established.

The most common variety of Hirado azalea is Rhododendron x pulchrum 'Oomurasaki' (also known as Oomurasaki, Oomurasaki Ryukyu, or Osakazuki), but I'm not aware of the differences between it and Hirado azalea. Generally, it is said that Rhododendron x pulchrum is the variety planted in urban areas.

Rhododendron x obtusum is the parent species of Rhododendron kiusianum, but I don't understand the difference between them. Some people think that Rhododendron kiusianum is the one with double petals, but I don't know the scientific explanation.

There are many other horticultural varieties, but since the differences are not at the species level, I will omit them.

Other species in the Rhododendron genus are introduced below.

While Kurume azaleas and mountain azaleas are somewhat similar, the main difference is that Kurume azaleas are only cultivated and have many short yellow hairs on their leaves, while mountain azaleas are usually found growing wild and have long white hairs on their leaves.

What's the difference between mountain azaleas and rhododendrons? We'll explain how to distinguish between similar species! Research has revealed that bumblebees are also essential for flowers that are supposedly specialized in attracting butterflies!

The Japanese azalea (Rhododendron kaempferi) is a representative species of wild azalea in Japan, while the Japanese azalea (Rhododendron molle) is famous for being poisonous. Both belong to the Rhododendron genus of the Ericaceae family and are representative species of red wild azaleas, so you might get them confused. However, you can distinguish them by checking the shape of their leaves and how the flowers are arranged. These two species...

ecological-information.com

References

Hayashi, Masayuki. 2019. Tree Leaves: Expanded and Revised Edition - Identifying 1300 Species Through Real-Life Scans. Yama-kei Publishers, Tokyo. 824pp. ISBN: 9784635070447

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

Leucothoe, American Leucothoe (European Leucothoe), and Leucothoe axillaris are representative evergreen shrubs of the Leucothoe genus in the Ericaceae family in Japan. They are similar in that their leaves have pointed tips and fine serrations, and Google search results often mix these species together, which can be confusing. Their Japanese names are also often confused. However, there is a significant difference: Leucothoe is naturally distributed in Japan and can only be found in forests, while American Leucothoe and Leucothoe axillaris are only cultivated in horticulture and can only be found in urban areas. Of course, there are also many morphological differences. American Leucothoe and Leucothoe axillaris seem to be quite confused in both Japan and the US, but it is probably best to check the shape of the flower sepals and the length of the petiole. The flowers have a urn-shaped corolla, which is common in the Ericaceae family, and are white. No research on pollinating insects has been found, but it is likely that bees are attracted to them. The fruit is a capsule that splits open when ripe, and the seeds are thought to be dispersed by gravity or wind. This article will explain the classification, morphology, pollination ecology, and seed dispersal of the genus Leucothoe.

What are Leucothoe japonica, American Leucothoe, and Leucothoe axillaris?

Leucothoe keiskei, also known as rock nanten, is a species endemic to Japan, distributed on Honshu (southern Kanto, southern Chubu, and Kii Peninsula). It is an evergreen shrub that grows on cliffs in deep mountains, hanging downwards (Kitamura and Murata, 1979).

American rock jasmine (Leucothoe fontanesiana) is distributed in the eastern United States (Alabama, Georgia, North Carolina, South Carolina, Tennessee, and Virginia) and is an evergreen shrub that grows in forests along streams, mountain canyons, and damp slopes (Flora of North America Committee, 2009). In Japan, it is somewhat commonly cultivated as a ground cover or ornamental plant in parks and gardens. Its alternative name is European rock jasmine, but it is not found in Europe, so this Japanese name is likely misleading.

Leucothoe axillaris, also known as Axillaris rock jasmine, is distributed in the eastern United States (Alabama, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, and Virginia). It is an evergreen shrub that grows in blackwater floodplains and coastal plains. In Japan, it is occasionally cultivated as a ground cover or ornamental plant in parks and gardens. There is no appropriate Japanese name for it, so here we will refer to it as Axillaris rock jasmine, based on its scientific name.

They all share the common characteristic of being evergreen shrubs belonging to the genus Leucothoe in the family Ericaceae. Their leaves are quite similar, with alternate arrangements, pointed tips, and fine serrations.

Other minor differences include the persistence of the bracts and bracteoles, the arrangement of the calyx lobes of the flowers in a tile-like pattern, the presence of projections on the anthers, the formation of capsules that dehisce dorsally, and the presence of small, numerous seeds (Kanagawa Prefecture Flora Survey Association, 2018).

American rock jasmine is so well-known that it appears in Google search results for the original rock jasmine, which can confuse people who have never seen it before.

Furthermore, American rock jasmine and axillaris rock jasmine, in particular, are native to North America, are well-known in horticulture for their use as ground cover and ornamental plants, and have very similar shapes. Perhaps because of this, not only are they often misidentified, but there is considerable confusion regarding their Japanese names in internet articles and sales sites. Some even mistakenly believe that the Japanese names for American rock jasmine and European rock jasmine are the same. This has become quite common, but it should be corrected as an error.

What are the differences between Leucothoe japonica and Leucothoe axillaris?

The main difference between these three species is that *Leucothoe japonica* is naturally distributed in Japan and is not usually cultivated (although it is occasionally grown in pots), while *Leucothoe axillaris* and *Leucothoe asiatica* are only cultivated. Therefore, you can basically tell right away whether you see *Leucothoe japonica* in a forest or *Leucothoe axillaris* in an urban area.

The genus Leucothoe has an interesting distribution, with three species known in East Asia and three in North America, and two species found in Japan (Kanagawa Prefecture Flora Survey Association, 2018). Due to the long period of isolation between the East Asian and North American species, there are significant differences in their morphology. Let's take a look at their morphology for confirmation (Flora of North America Committee, 2009; Hayashi, 2019).

First, while the petioles of the common leucocephala (Iwanan) are hairless and green, those of American leucocephala (Axillaris) and leucocephala axillaris (Iwanan) are finely hairy and red.

Furthermore, while the underside of the leaves of Leucothoe japonica is hairless, Leucothoe americana has fine, brownish appressed hairs, and Leucothoe axillaris has hairless to sparsely hairy leaves.

Regarding the flowers, *Leucothoe japonica* has a few flowers, 1 to 7 per inflorescence, with large corollas measuring 17 to 23 mm and green calyxes, while *Leucothoe americana* and *Leucothoe axillaris* have many flowers, 8 to 60 per inflorescence, with small corollas measuring 5 to 8 mm and white calyxes.

It should be noted that another species of tree found in Japan , Leucothoe grayana, is completely different, with deciduous, papery leaves and prominently visible veins.

What are the differences between American rock jasmine and rock jasmine (Leucothoe axillaris)?

The problem lies in the difference between American leucothoe and axillaris leucothoe. These two are often confused on various websites. However, a look at an American botanical guide reveals the following differences (Flora of North America Committee, 2009).

First, the identification key points out that in American rock jasmine, the sepals are lanceolate with acute or subacute tips and the inflorescence is 4-10 cm long, while in rock jasmine axillaris, the sepals are broadly ovate with obtuse or rounded tips and the inflorescence is 2-4 (-5) cm long.

However, the only way to distinguish between them is by their flowering period. I was also able to find differences in the leaves by comparing the descriptions.

Regarding the petioles, American rock jasmine has long petioles measuring 10-15 mm, while American rock jasmine has short petioles measuring 5-10 mm.

Furthermore, regarding the leaf tips, in American rock jasmine, the tips are acute to long-pointed, and some are quite close to caudate, whereas in rock jasmine axillaris, they are acute to abruptly short-pointed.

In addition to these, although there are exceptions, the varieties cultivated in Japan for American leucothoe are mostly variegated varieties such as 'Rainbow', while for axillaris leucothoe, many varieties change color in autumn. This could be a significant clue in Japan. However, I am still not sure how many true axillaris leucothoe varieties are actually cultivated.

What is the structure of a flower?

The genus Leucothoe shares a common characteristic with other plants in the Ericaceae family: a urceolate corolla (a type of urn-shaped corolla). As the name suggests, the corolla is modified to resemble a urn.

Leucothoe var. japonica blooms from July to August. The flower stalks emerge from the leaf axils of the previous year's branches, are 1-9 cm long, and bear 1-7 flowers in a raceme. The individual flowers hang downwards. The bracts are broadly ovate, 1 mm long, and the bracteoles are also broadly ovate, 1 mm long, with two at the base of the flower stalk. The flower stalk is 7-12 mm long. The calyx is 3 mm long, 5-lobed, with each lobe blunt at the tip and covered with fine hairs along the edges. The corolla is white and cylindrical, 17-23 mm long, with 5 lobes at the tip, each lobe curving backward. The style is 13-18 mm long. There are 10 stamens, and the filaments are densely covered with hairs. The anthers are bifurcated, each with an opening at the tip and two awn-like projections.

American rock jasmine blooms in mid-spring, and in Japan from April to May. The inflorescences are clustered or solitary, dense, without peduncles, and bear 20 to 60 flowers, measuring 4 to 10 cm in length. The bracts are persistent, ovate-triangular, and 1.7 to 2.2 mm long. The pedicels are 2 to 2.5 mm long. The flowers have white, lanceolate-ovate sepals, 1.7 to 2 mm long, with acute or nearly acute tips. The corolla is cylindrical, 5 to 7 mm long. The filaments are papillate (sometimes with spreading hairs). The anthers are 1.2 to 1.5 mm long, with the half-anthers spreading at the tip.

Leucothoe axillaris flowers from early to mid-spring. The inflorescence is fascicular or solitary, dense, without a peduncle, bearing 8 to 30 flowers, and measuring 2 to 4 (up to 5) cm in length. The bracts are deciduous, ovate, and 2 to 2.5 mm long. The pedicels are 2.2 to 2.5 mm long. The flowers have white, broadly ovate sepals, 1.5 to 2 mm long, with obtuse or rounded tips. The corolla is cylindrical, 6 to 8 mm long. The filaments are spreading and papillate. The anthers are 0.7 to 1.2 mm long, with two awns, and the upper part of the anthers is splayed.

How is pollination done?

The structure is clearly conspicuous to insects, suggesting that it is an insect-pollinated flower, but no research on visiting insects has been found in either Japan or the United States. However, the Ericaceae family generally limits its visiting insects to certain types of bees due to its downward-facing flowers, and the same may be true for the Leucothoe genus. It is intriguing to know what kinds of insects visit the small flowers of Leucothoe var. japonica.

What is the structure of the fruit?

The fruits of the genus Leucothoe are all capsules. A capsule is a type of dry fruit, and a single fruit consists of multiple fused, sac-like pericarps.

When the flowers of the Nandina domestica develop into fruit, the flower stalks thicken at the tip, curve, and point upwards. The capsules are flattened and spherical, with a diameter of 7 mm.

The capsules of American rock jasmine are 5-6 mm wide. The seeds are oval or oblong. The seed coat is hard and reticulated.

The capsules of Leucothoe axillaris are 4.5-5-6 mm wide. The seeds are angular. The seed coat is hard and papillate.

What are the seed dispersal methods?

Since capsules generally split open when ripe, exposing and scattering the seeds, gravity dispersal is likely a method of seed dispersal. In species with horn-shaped seeds, wind dispersal may also be a factor, and one Japanese study treated the related species, *Hypochaeris radicata*, as a wind-dispersing plant (Tsuyuzaki & Miyoshi, 2009). Similar possibilities seem likely for other species, but there has been little research on their dispersal capabilities.

References

Flora of North America Committee. 2009. Flora of North America (Vol. 12 Magnoliophyta: Paeoniaceae to Ericaceae). Oxford University Press, Oxford. 585pp. ISBN: 9780195340266

Hayashi, Masayuki. 2019. Tree Leaves: Expanded and Revised Edition - Identifying 1300 Species Through Real-Life Scans. Yama-kei Publishers, Tokyo. 824pp. ISBN: 9784635070447

Tsuyuzaki, S., & Miyoshi, C. 2009. Effects of smoke, heat, darkness and cold stratification on seed germination of 40 species in a cool temperate zone in northern Japan. Plant Biology 11(3): 369-378. https://doi.org/10.1111/j.1438-8677.2008.00136.x

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

Kitamura, Shiro & Murata, Gen. 1979. Illustrated Flora of Japan in Color: Woody Plants, Vol. 2. Hoikusha, Osaka. 630pp. ISBN: 9784586300501

The Japanese azalea (Rhododendron kaempferi) is a representative species of wild azalea in Japan, while the Japanese azalea (Rhododendron molle) is famous for being poisonous. Both belong to the Rhododendron genus of the Ericaceae family and are representative species of red wild azaleas, so you might get them confused, but you can distinguish them by checking the shape of the leaves and how the flowers are arranged. In addition to the characteristic common to the Rhododendron genus that makes the flowers easily pollinated by butterflies, the flowers of these two species are specially targeted to butterflies by being bright red. However, as research has progressed in recent years, it has been suggested that bumblebees also visit the flowers and may play an important role in pollination. This article will explain the differences between the Japanese azalea and the Japanese azalea, and the pollination ecology of their flowers.

A representative species of wild azalea

Rhododendron kaempferi var. kaempferi, also known as mountain azalea, is distributed in southern Hokkaido, Honshu, Shikoku, and Kyushu. It is a semi-evergreen shrub that inhabits sparse forests in low mountainous areas, forest edges, sunny ridges, and grasslands (Nishida, 2000; Mogi et al., 2003). It has the widest distribution range of any wild azalea in Japan and is a representative species of wild azalea that thrives in acidic soil. It has spring leaves that emerge in spring and fall in autumn, and summer leaves that emerge from summer to autumn. A unique feature is that many of the summer leaves overwinter.

Rhododendron molle subsp. japonicum (synonym: Rhododendron japonicum), also known as the lotus azalea, is a deciduous shrub distributed in southwestern Hokkaido, Honshu, Shikoku, and Kyushu, growing in clusters in cool, sunny locations such as plateau pastures and wetlands. It is poisonous, and is known to contain grayanotoxin throughout the plant, and rhodojaponin in the flowers and roots (Yong-Qing et al., 2018). Grayanotoxin is also found in nectar and honey, and there have been cases of poisoning (Satake, 2012; Saito, 2021).

Both belong to the Rhododendron genus of the Ericaceae family and are representative species of wild red azaleas, so you may sometimes have trouble distinguishing them.

What are the differences between Rhododendron kaempferi, Rhododendron molle, and Rhododendron parvifolium?

However, these two types can be distinguished as follows:

First, while there is a closely related species to the Japanese azalea called Rhododendron transiens, they can be easily distinguished by the fact that the Japanese azalea has 5 stamens, while Rhododendron transiens has 10 stamens (sometimes 6-9) (Kanagawa Prefecture Flora Survey Association, 2018).

Regarding the difference between Rhododendron kaempferi and Rhododendron molle, Rhododendron kaempferi has leaves that are neatly ovate to elliptical with a relatively large amount of brown hairs on both sides, while Rhododendron molle has particularly long, narrow leaves with a rounded, spatulate tip and a noticeably wrinkled surface, so they can also be easily distinguished (Hayashi, 2014). However, some young Rhododendron molle leaves seem to have pointed tips.

Are there any other similar species?

The genus Rhododendron is an extremely vast group, and the flower shapes are very similar, so there may be other species that you might be confused with.

For information on other species in the Rhododendron genus, please see the separate article.

While Kurume azaleas and mountain azaleas are somewhat similar, the main difference is that Kurume azaleas are only cultivated and have many short yellow hairs on their leaves, while mountain azaleas are usually found growing wild and have long white hairs on their leaves.

What are the differences between Hirado azalea, Kurume azalea, and Satsuki azalea? An explanation of how to distinguish between similar species.

Hirado azalea, Kurume azalea, and Satsuki azalea (Satsuki rhododendron) all belong to the genus Rhododendron in the family Ericaceae, and are three species that are extremely commonly cultivated even in urban areas. However, since the shape of their flowers is almost identical, some people may have trouble distinguishing them. The three species can be distinguished by the shape of their leaves...

ecological-information.com

Bright red flowers found in the wild in Japan

The flowers of the mountain azalea and the rhododendron are bright red, which is the most distinctive feature of these two species. There are probably few species in the mountains of Japan that have such red flowers.

Both Rhododendron kaempferi and Rhododendron molle belong to the Rhododendron genus of the Ericaceae family, so their basic flower structure is the same. The corolla is funnel-shaped, and since it is a sympetalous flower, the base is fused, and it is divided into 5 lobes, appearing as 5 petals. The calyx is also divided into 5 lobes. There are 5 stamens, and one pistil protrudes longer than the stamens.

Where is the nectar? It's in a slightly hard-to-find location. If you observe the flower from the outside, you'll notice a single vein on the upper lobe of the corolla (petal). The cross-section of this vein is Ω-shaped, meaning it's a tube (Tanaka, 2001). This tube is formed by the lobes twisting together and becoming wrinkled. The nectar is located deep inside this tube.

In other words, to suck nectar, an insect needs to have a very long, slender mouthpart to pass through. Such insects would be extremely limited in number.

The mountain azalea blooms from April to June, and its flowers are basically vermilion in color, with dark spots on the upper lobes of the corolla.

Rhododendron molle blooms from May to June, and its flowers are often arranged in a ring of 2 to 8 flowers facing sideways. This resemblance to the shape of the lotus flower (Astragalus sinicus) is the origin of its name. The flowers are basically reddish-orange, although there are variations in shade. The upper lobes of the corolla have orange-yellow spots.

Although there are subtle differences between these two species, their flowers are quite similar, and it is expected that their basic ecology is also similar.

Flowers of the Ericaceae family are special to butterflies.

Flowers of the Rhododendron genus, including mountain azaleas and molle azaleas, are familiar to us because many varieties are cultivated, which might give the impression that they are unremarkable. However, the fact that their stamens and pistils protrude far forward, and that their petals have thin tubes, is clearly a unique structure in nature. Furthermore, the fact that they are used in horticulture means that their flowers have more vibrant colors compared to other plants. What kinds of insects are attracted to such flowers?

These plants are primarily visited by butterflies, especially swallowtail butterflies (Tanaka, 2001).

Swallowtail butterflies have very long proboscises, and in ordinary flowers, they only steal the nectar without touching the stamens or pistils, thus not contributing to pollination. To counter this, the tubes leading to the nectar, as well as the stamens and pistils, have become longer to make contact with the swallowtail butterfly's body.

The stamens have a special feature not found in other plants. At the tip of the stamen are two small, brownish volvae (anthers) side by side. The anthers lack lids, so the white pollen is visible.

When a person picks up the pollen with pointed tweezers, many grains of pollen stick together and slide out easily. This is because the pollen grains are connected by threads called "adhesive threads."

When a swallowtail butterfly comes to a flower in search of nectar, its body comes into contact with the white pollen that is slightly visible from the tip of the anther. From there, a clump of pollen slides out via an adhesive thread, sticking to the swallowtail butterfly's body, and the pollen is transferred.

You might wonder how they manage to make contact with the stamens so effectively, but there's a clever design behind it. The corolla opens wide like a trumpet, which prevents the beetle from using it as a foothold. On the other hand, the stamens and pistil rise upwards and are positioned below the entrance to the nectar tube. This ensures that the beetle must use the stamens as a foothold to drink the nectar.

Furthermore, the vibrant colors are specifically designed to attract butterflies. The red color of mountain azaleas and rhododendrons, in particular, holds special significance. Although not widely known, only a select few insects that visit flowers, such as butterflies, can see red, while bees cannot perceive it. For this reason, mountain azaleas strongly attract butterflies.

The dark or orange-yellow spots on the petals are also called "nectar guides," and are thought to make it easier to identify the entrance to the tube in the petal that leads to the nectar.

Specific species recorded on Rhododendron kaempferi include Atrophaneura alcinous alcinous and Papilio xuthus (Yokogawa & Hotta, 1995), Parnassius glacialis and Papilio maackii (Takahashi & Itino, 2017).

There is a record of the Papilio maackii butterfly on Rhododendron molle (Takahashi & Itino, 2017).

However, these are records from high-altitude areas, so it's more likely that more common swallowtail butterflies visit in lowland areas.

Bumblebees also come, but are they not wanted by the mountain azaleas?

While mountain azaleas and rhododendrons are specifically targeted by butterflies, it has been confirmed that completely different insects also visit them (Tanaka, 2001).

That's a bumblebee. Bumblebees have various mouth lengths, but some species, like the tiger bumblebee, have long mouths that can just barely reach the back of the tubes of the mountain azalea (Tanaka, 1997). Also, because they reflect ultraviolet light, even bumblebees that cannot see red can apparently identify the flowers (Tanaka and Hirano, 2000).

Although their mouthparts aren't as long as a butterfly's, they still manage to land properly on the stamens and pistils, so pollination should be no problem. However, there's a theory that bumblebees are undesirable for mountain azaleas. Why is that?

Bumblebees efficiently visit nearby flowers in sequence. Therefore, they are highly likely to revisit their own flower next to it (neighbor pollination). This leads to self-pollination, preventing genetic diversity. Butterflies, on the other hand, flit about aimlessly, visiting flowers on relatively random individuals, thus maintaining genetic diversity.

But then again, maybe we need bumblebees too?

However, a study by Shinshu University, published in 2017 (Takahashi & Itino, 2017), further investigated whether mountain azaleas (and rhododendrons) are truly independent of bumblebees. This study was conducted in the central mountainous region of Nagano Prefecture. The mountainous region of Nagano Prefecture is characterized by low temperatures due to its location in the northern part of Japan and its mountainous terrain.

In locations like this, butterfly diversity is low due to tolerance to low temperatures, while bumblebee diversity is high. However, mountain azaleas and rhododendrons are commonly found in these locations. Which of these two species is visited more frequently in such places?

To understand this, this study investigated the insects that visit flowers and the sugar content of nectar (different insects prefer different sugar content in nectar).

As a result, two species of bumblebees, Bombus ardens and Bombus diversus, were found more frequently on mountain azaleas than butterflies, while three species—Bombus ardens, Bombus diversus, and Bombus hypocrita— were found more frequently on rhododendrons than butterflies. In addition, the bumblebees were covered in pollen.

The sugar content of nectar ranged from 51 to 541 TP3T for mountain azaleas and from 30 to 451 TP3T for rhododendrons. Bumblebees prefer a sugar content of 30 to 551 TP3T, while butterflies prefer 17 to 401 TP3T. Therefore, mountain azaleas have a sugar content that is preferred by bumblebees, while rhododendrons have a sugar content that covers both.

These results suggest that bumblebees likely play a more important role in pollination in the mountainous regions of Nagano Prefecture than previously thought!

This result demonstrates the flexibility of the mountain azalea flower. While the flower shape is thought to have evolved for butterfly pollination, it may have undergone some kind of change to allow for pollination by bumblebees in mountainous regions. How it avoids cross-pollination is also unknown. Further research may reveal more details in the future!

Furthermore, there is considerable variation in the sugar content of nectar, and it has been reported that the sugar content increases rapidly after flowering. Therefore, caution may be needed when interpreting this data. This point also remains a mystery.

Why did the Rhododendron molle evolve to be poisonous?

Why did the Rhododendron molle evolve to have poisonous flowers? Several other species of the Rhododendron genus are known to be poisonous. It's puzzling that even the nectar contains toxins, let alone the leaves.

The primary role of pollinators is thought to be to block pollinators with low pollination effectiveness and to suppress excessive harvesting by foragers (herbivores) (Feng et al., 2024).

Therefore, the poison in the Rhododendron molle is effective against both insects and mammals, including humans.

Although not related to Rhododendron molle, it has been confirmed that honeybees and small bees avoid the nectar of other species in the Rhododendron genus.

It appears that the Rhododendron japonicum selectively attracts insects (butterflies and bumblebees) that are resistant to the toxins in its nectar.

Furthermore, research is revealing that even among pollinators resistant to toxins, some species are selecting insects that are more nectar-eating by increasing the toxicity of their pollen.

However, comprehensive research into why some azaleas are poisonous while others are not is still lacking.

The fruit is a capsule, and the seeds are dispersed by wind.

The fruit, common to all species in the Rhododendron genus, is a capsule. Generally, the capsule's pericarp ruptures, scattering the seeds inside.

The capsules of the mountain azalea are oval-shaped, narrowing at the tip, and covered with flat, brownish hairs. They mature and dehisce between August and October.

The capsules of Rhododendron molle are cylindrical, 2-2.5 cm long, and densely covered with brown bristles. The seeds are about 2 mm long, winged, and have serrated appendages at the base.

The capsules of the Rhododendron genus do not have any special structure, but because the seeds are very small and sometimes have wings, it is thought that they are dispersed not only by gravity but also by wind, with the seeds flying away from the fruit when it ripens and splits open (Kobayashi, 2007).

References

Feng, HH, Lv, XW, Yang, XC, & Huang, SQ 2024. High toxin concentration in pollen may deter collection by bees in butterfly-pollinated Rhododendron molle. Annals of Botany 134(4): 551-560. https://doi.org/10.1093/aob/mcae047

Hayashi, Masayuki. 2014. 1100 Tree Leaves Identified Through Real-Life Scans. Yama-kei Publishers, Tokyo. 759pp. ISBN: 9784635070324

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

Kobayashi, Masaaki. 2007. From Flower to Seed: The Science of Seed Dispersal. National Rural Education Association, Tokyo. 247pp. ISBN: 9784881371251

Nishida, Naomichi. 2000. Trees of Japan. Gakken Plus, Tokyo. 256pp. ISBN: 9784054011199

Saito, Katsuhiro. 2021. The Beautiful and Terrifying World of Poisons! A Visual Encyclopedia of 200 Poisons. Shuwa System, Tokyo. 271pp. ISBN: 9784798063652

Satake, Motoyoshi. 2012. Poisonous Plants of Japan. Gakken Plus, Tokyo. 232pp. ISBN: 9784054052697

Takahashi, K., & Itino, T. 2017. Visitation frequencies of bumblebees and swallowtail butterflies to flowers and the nectar sugar concentration of Rhododendron kaempferi and R. japonicum in mountains of central Japan. Journal of Pollination Ecology 21: 92-97. ISSN: 1920-7603, https://doi.org/10.26786/1920-7603(2017)438

Tanaka, Hajime. 2001. Flowers and Insects: A Collection of Discoveries of Mysterious Deception. Kodansha, Tokyo. 262pp. ISBN: 9784062691437

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

Mogi, T., Takahashi, H., Katsuyama, T., & Ishii, E. 2003. Flowers Blooming on Trees: Sympetalous Flowers, Monocotyledons, Gymnosperms. Yama-kei Publishers. Tokyo, 719pp. ISBN: 9784635070058

Yokogawa, Mizuki & Hotta, Mitsuru. 1995. Plant Notes of Southwest Japan II. Trait variation of various populations of Rhododendron kiusianum, Rhododendron kiusianum, and Rhododendron japonicum in the Kirishima Mountains. Plant Classification, Geography 46(2): 165-183. ISSN: 0001-6799, https://doi.org/10.18942/bunruichiri.KJ00001079099

Yong-Qing, CAI, Jian-Hui, HU, Jie, QIN, Tao, SUN, & Xiao-Li, LI 2018. Rhododendron Molle (Ericaceae): phytochemistry, pharmacology, and toxicology. Chinese Journal of Natural Medicines 16(6): 401-410. https://doi.org/10.1016/S1875-5364(18)30073-6

Monotropa uniflora, Monotropa uniflora var. japonica, and Monotropa uniflora are three species of plants that grow in the dark forest floor, where photosynthesis has been lost. They lack normal leaves, which have degenerated into scale leaves. They only have stems and flowers, and their entire bodies are white because they lack chlorophyll. They are known as mycoheterotrophic plants, but distinguishing them can be difficult without experience. However, upon closer inspection, various differences can be observed. Monotropa uniflora and Monotropa uniflora var. japonica belong to the Ericaceae family, while Monotropa uniflora var. japonica belongs to the Orchidaceae family, so their flower structure and ecology are completely different. Monotropa uniflora and Monotropa uniflora var. japonica belong to the same Ericaceae family, but their flowering period, inflorescence, flowers, ovary, and fruit differ. Recently, Monotropa uniflora var. kirishimaensis, which has red flowers, has been discovered, so it is also necessary to distinguish it from these species. These species have stopped photosynthesizing and depend on fungi for nutrients. There are several reasons for this, but the idea that it is the most adaptive for growing in the dark forest floor is easy to understand. The pure white flowers of Monotropa uniflora and Monotropa uniflora appear colored to the eyes of insects, and their downward-facing structure makes them most frequently visited by bumblebees, who contribute significantly to pollination. On the other hand, Monotropa uniflora is self-pollinating. These are also thought to be adaptations to the dark forest floor. The fruit of Monotropa uniflora is a berry, and its seeds are known to be dispersed by cockroaches, but Monotropa uniflora has a capsule, and its seeds are dispersed by wind, which is the opposite. This may be influenced by the fruiting period. This article will explain the classification, evolution, pollination ecology, and seed dispersal of Monotropa uniflora, Monotropa uniflora, and Monotropa uniflora.

Three plant species that grow in the dark forest floor where photosynthesis has been lost

Monotropastrum humile, also known as silver dragon grass or ghost mushroom, is a perennial herb distributed in the southern Kuril Islands, Hokkaido, Honshu, Shikoku, Kyushu, and Ryukyu Islands of Japan; Sakhalin, the Korean Peninsula, China, Taiwan, Myanmar, northern India, and the Himalayas. It inhabits the forest floor of coniferous and broadleaf forests. It mainly grows on moist humus, and its finely branched roots usually form a clump. Its Japanese name, "Ginryusou" (silver dragon grass), is said to come from the resemblance of its appearance, enclosed in vestigial scale-like leaves, to a dragon covered in scales. It belongs to the genus Monotropastrum in the family Ericaceae.

Monotropa uniflora, also known as autumn silver bellflower, is a perennial herb widely distributed in Hokkaido, Honshu, Shikoku, and Kyushu in Japan; as well as in the temperate regions of Southeast Asia and North America. It grows in somewhat shady areas within hilly and mountainous forests. Its Japanese name comes from its resemblance to the silver bellflower (Monotropa uniflora). It belongs to the genus Monotropa in the family Ericaceae.

Epipogium roseum, also known as Tashiro Orchid, is distributed in Honshu (south of Gunma Prefecture), Shikoku, Kyushu, and the Ryukyu Islands in Japan; China, Taiwan, Southeast Asia, India, Australia, New Caledonia, and West Africa. In Japan, it is a perennial herb that grows in evergreen broad-leaved forests. Its Japanese name comes from the name of its discoverer, Zentaro Tashiro, and was given by Dr. Tomitaro Makino. It belongs to the genus Epipogium in the family Orchidaceae.

Neither of them has normal leaves; their leaves have degenerated into scale-like leaves. They only have stems and flowers, and their entire bodies are white because they lack chlorophyll. They are known as mycoheterotrophic plants (i.e., mycoparasitic plants, saprophytic plants). Because their entire bodies are white, it can be difficult to distinguish them without experience. In particular, Monotropa uniflora and Monotropa uniflora look very similar in shape.

What are the differences between Monotropa uniflora, Monotropa uniflora var. japonica, and Monotropa uniflora?

However, upon closer examination, various differences can be observed (Kanagawa Prefecture Flora Survey Association, 2018).

First, while Monotropa uniflora and Monotropa uniflora belong to the Ericaceae family, Tashiro orchid belongs to the Orchidaceae family, so their flower structures and ecology are completely different.

While numerous scale-like leaves can be seen in Monotropa uniflora and Monotropa uniflora var. japonica, in Monotropa japonica var., there are only about 1 to 8 scale-like leaves, spaced apart.

Furthermore, regarding the inflorescence, while Monotropa uniflora and Monotropa uniflora var. japonica have only one to a few flowers that hang downwards, Monotropa japonica produces a raceme inflorescence with 2 to 16 flowers.

Regarding the structure of the flower, in Monotropa uniflora and Monotropa uniflora var. japonica, the calyx and petals overlap to form a tubular bell shape, but in Orchidaceae, there is a unique shape called the "orchid-shaped corolla" common to all plants in the Orchidaceae family, consisting of three sepals and three petals, with two "lateral petals" and a central "labellum" combined.

Although Monotropa uniflora and Monotropa uniflora var. japonica belong to the same Ericaceae family, they differ in their flowering period, inflorescence, flowers, ovary, and fruit.

Regarding the flowering period, Monotropa uniflora flowers in April-May and July, while Monotropa uniflora var. japonica flowers in September-October.

Regarding the inflorescence, in Monotropa uniflora, one to several flowers hang downwards at the tip of the stem, whereas in Monotropa uniflora var. japonica, only one flower is attached to the end of the stem.

Regarding the flowers, in Monotropa uniflora, the sepals and upper parts of the petals are not notched, whereas in Monotropa uniflora var. japonica, there are irregular notches (serrations, teeth) on the upper parts of the sepals and petals.

Regarding the ovary, in Monotropa uniflora, it has one chamber and the ovule is a parametrial placenta, whereas in Monotropa uniflora var. japonica, the ovary has 3 to 5 chambers and is axillary placenta.

Regarding the fruit, Monotropa uniflora has a berry that does not split open when ripe, grows obliquely sideways, and retains its sepals and petals even when fruited, whereas Monotropa uniflora has a capsule that splits open when ripe, grows upwards, and its sepals and petals fall off when fruited.

Regarding the seeds, Monotropa uniflora lacks wings, while Monotropa uniflora var. japonica does.

I've listed quite a few differences, but practically speaking, you can distinguish them simply by checking the flowering period and the way the petals are lobed.

Furthermore, a variety of Monotropastrum , Monotropastrum humile f. roseum, has been identified that has a red ovary inside the flower.

Also in the same family, Ericaceae, subfamily Monotropinae, is * Hypopitys monotropa*, but it can be easily distinguished by the fact that it has 4 to 8 flowers in a raceme at the end of the stem, the plant body is pale yellowish-brown, and the flowers bloom from June to August.

What is the difference between Monotropa uniflora and Monotropa kiusiana?

Furthermore, there is a species called Monotropastrum kirishimense, which has recently been discovered as a new species similar to Monotropastrum verum (Suetsugu et al., 2023). Currently, it has been confirmed in Osaka, Wakayama, Shizuoka, Gifu, Kagoshima, and Miyazaki prefectures. The differences between it and Monotropastrum verum are quoted below.

• While the petals and sepals of *Monotropa uniflora* are reddish, those of *Monotropa uniflora* are transparent to white. Similarly, *Monotropa uniflora* (a color variant of *Monotropa uniflora*) also appears reddish. However, the actual color comes from the ovary inside the flower; the color of the ovary is simply showing through, and the petals and sepals are actually transparent to white.
• The number of sepals in Monotropa uniflora is 4 to 11, which is more than the usual 2 to 3 in Monotropa uniflora. Also, in Monotropa uniflora, the sepals are always in contact with the petals, whereas in Monotropa uniflora they are often separated from the corolla tube.
• The flowers of *Monotropa uniflora* are rounder than those of *Monotropa uniflora* from the early stages of flowering.
• The above-ground portion of *Monotropa uniflora* is often short, less than 5 cm. (*Monotropa uniflora* is often 5 cm or longer.)
• The rhizomes of Monotropa uniflora are often long, exceeding 10 cm. (Monotropa uniflora rhizomes are usually less than 5 cm.)
• The roots of *Monotropa uniflora* are less distinct than those of *Monotropa uniflora*, blending seamlessly with the surrounding soil, and their tips barely protrude, making them almost invisible to the naked eye. (A cluster of white mycelium can be seen.)

『Kobe University Press Release』

What is the adaptive significance of ceasing photosynthesis?

The three species Monotropa uniflora, Monotropa uniflora var. japonica, and Monotropa japonica are known as mycoheterotrophic plants (i.e., mycoparasitic plants, saprophytic plants).

"Heterotrophy" is the opposite of "autotrophy," which synthesizes nutrients on its own through photosynthesis, etc. Heterotrophy is a way of life that relies on obtaining nutrients from other organisms. This applies to many animals, including humans.

In the case of Monotropa uniflora, Monotropa uniflora var. japonica, and Monotropa uniflora, they do not perform photosynthesis but instead steal carbon, which is a nutrient, from fungi (the kind called mushrooms and molds) that grow on trees through their roots.

They were once commonly called "saprophytic plants" because they were thought to be able to obtain nutrients from decaying leaves and soil. While they are still sometimes referred to this way out of convention, it's not a very desirable term.

In the case of Monotropa uniflora, it is known that the majority of mycorrhizal fungi are ectomycorrhizal fungi of trees (Russulaceae, Russula genus), and that a wide range of species within the Russula genus are utilized as mycorrhizal fungi (Yokoyama et al., 2013).

In the case of *Psathyrella tashiroensis*, it has been found to form mycorrhizal symbiosis with fungi of the family Psathyrellaceae (Tanigame, 2011).

Why did mycoheterotrophic plants stop photosynthesis and start obtaining nutrients from fungi?

There are two possible explanations for this (Suetsugu & Kato, 2014).

The most common reason is that parasitizing fungi allows them to survive even in the dark forest floor where there are few competitors. Photosynthesis is a method of nutrient synthesis that does not depend on other organisms, but on the other hand, it can be said that it is a way of life that is highly dependent on light. In the dark forest floor where there is little light, it can be said that a way of life that depends on other organisms is quite advantageous. In fact, Monotropa uniflora, Monotropa uniflora var. japonica, and Monotropa uniflora all live in the shade, so it is quite plausible that they have such advantages.

Another reason is that, when stressed, they can survive by remaining underground instead of extending their plant bodies above ground. While ordinary photosynthetic plants also keep their plant bodies underground, in that case, they still use nutrients through respiration and other metabolic processes while confined underground. By parasitizing fungi, they can obtain carbon and increase their survival rate.

The pure white flowers of the Indian pipe plant are exclusively for bumblebees! What's the reason?

The flowering period for Monotropa uniflora is from spring to summer (April-May and July). The inflorescence has a flower stalk and is 10-20 cm tall. The flowers bloom facing downwards and are tubular-bell shaped. The petals and calyx are oblong and pure white. There are 1-5 sepals and 3-5 petals. Although not visible in the photo, the stigma of the pistil is a purple disc that occupies most of the flower, and 6-10 stamens are arranged alternately in two rows around the pistil.

Although the flowers appear plain white to the human eye, they reflect ultraviolet light, making them conspicuous to insects (Klooster et al., 2009).

What kinds of insects visit this flower?

Studies conducted by various research groups in Japan have consistently shown that the site is visited almost exclusively by bumblebees of the genus Bombus, primarily Bombus diversus diversus (Tanaka, 1978; Ushimaru & Imamura, 2002; Sueji & Kato, 2014).

It is said that Monotropa uniflora flowers can bloom in dense clusters within an area of about 20 cm square. When a bumblebee comes to try to drink the large amount of nectar deep inside, its head and legs attach to the stamens located next to the pistil.

Because the flowers face downwards, only bumblebees that can skillfully hang down can insert their mouths, the depth to the nectar is suitable for the length of a bumblebee's mouth, and the entrance to the nectar is closed, it is a somewhat unusual flower, but it can be said to be a flower form that is well-suited for bumblebees (Tanaka, 1978).

The bumblebees that visit are thought to be queen bees that begin their activity in the spring, but it has been suggested that worker bees may also come (Ushimaru & Imamura, 2002).

Why does the Indian pipe plant rely on bumblebees for pollination?

For Monotropa uniflora, a mycoheterotrophic plant that grows in the dark forest floor, relying on pollination from insects that prefer bright environments, such as small bees and honeybees, is extremely difficult. On the other hand, bumblebees can regulate their body temperature and therefore forage even in dark environments. For this reason, it is thought that the shape of the flower has evolved to be specialized for bumblebees (Suetsugu & Kato, 2014).

There is considerable variation in flower size (Ushimaru & Imamura, 2002). While larger flowers might seem more attractive to insects and thus have a higher chance of pollination, this tendency has not been demonstrated in studies. The reason for the small flowers remains unknown. This flower still holds many mysteries.

It's also quite unusual that the ovary of the red-flowered silver pipe plant turns red.

Are the insects that visit Monotropa uniflora the same as those that visit Monotropa uniflora?

The flowering period of Monotropa uniflora is from September to October. The inflorescence has a flower stalk and is 10 to 30 cm tall. The flowers bloom facing downwards and are tubular-bell-shaped. The petals and calyx are lanceolate to oblong and pure white. There are 3 to 5 sepals and 3 to 8 petals. Although not visible in the photo, the stigma of the pistil is a yellowish-brown disc that occupies most of the flower, and there are usually 10 stamens arranged around the pistil.

In the case of Monotropa uniflora, the flowers also reflect ultraviolet light, making them conspicuous to insects (Klooster et al., 2009).

Although there are differences in flowering period and the number of stamens, the basic structure is the same as that of Monotropa uniflora. Are the insects that visit this flower the same as those that visit Monotropa uniflora?

While no research in Japan could be found, a study conducted in Ohio, Indiana, Kentucky, and Tennessee in the eastern United States revealed that while the Bombus spp., which is found only in Honshu, the Korean Peninsula, and Ussuri, was not present, several species of the genus Bombus were indeed visiting (Klooster & Culley, 2009). Syrphidae were the next most frequent visitors, followed by a small number of Apidae, but their contribution to pollination may be low due to the downward-facing flowers. It seems reasonable to conclude that the genus Bombus is the most important pollinator.

Incidentally, this study also investigated pollinating insects of closely related species not found in Japan, such as *Monotropa uniflora* and *Monotropsis odorata*, and in these species as well, multiple species of the genus *Bumblebee* were found to be the most important pollinators.

However, it was found that there are significant differences in how pollen adheres to bumblebees between the genera Monotropa and Monotropa and the genus Monotropis.

In the genera Monotropa and Monotropa, as mentioned above, pollen adheres to the heads and thoraxes of bumblebees as they search for nectar in the flowers. This occurs because the anthers have slits, and the pollen falls off along these slits, spilling onto the inner wall of the corolla.

On the other hand, in the genus Monotropis, the anthers have two pores, and pollen is not easily released from the anther sac.

So how do bumblebees get pollen? Bumblebees hang from flowers and vibrate their wings rapidly. This causes pollen to fall out through the holes in the anthers. This is called "vibration pollination," and it is a well-known pollination method in the Solanum genus, which includes eggplant. It prevents nectar robbing and ensures that pollen is only passed to bees that can vibrate, such as bumblebees.

But ultimately, do these differences reflect any ecological differences?

Although not mentioned in this paper, it would be reasonable to assume that the genus Monotropis has flowers that are more specifically adapted to bumblebees.

In fact, records of pollinating insects show that while hoverflies and bees visited a small number of flowers in the Monotropa genus and Monotropa uniflora, their numbers were considerably reduced in the Monotropis genus.

While it's generally said that he specialized in bumblebees, perhaps he could be considered relatively generalist within the Pyrolainae subfamily.

There are still other questions remaining. Queen bumblebees, which become active in spring, visit Monotropa uniflora, but what kinds of bumblebees, and within the same species caste, visit Monotropa uniflora? This point also remains unclear.

Did the flowers of the Tashiro orchid only self-pollinate?!

Tashiro orchids bloom from June to July. They produce racemes at the top of the stem, bearing 2 to 16 flowers. The racemes are 10 to 20 cm long and extend above the flowerless bracts. The flowers open from the bottom upwards. The bracts usually have reddish-purple spots. The flowers have a characteristic "orchid-shaped corolla" common to all plants in the orchid family, consisting of three sepals and three petals, with two "lateral petals" and a central "labellum" combined. The sepals are linear-lanceolate, with nearly pointed tips. The lateral petals resemble the sepals but are slightly shorter, wider, narrowly ovate-lanceolate, and acute to obtuse. The labellum, when spread, is broadly ovate, with reddish-purple spots, and its edges are finely serrated. There is a spur at the base of the labellum, which is oblong (cylindrical), with a rounded tip, and protrudes towards the ovary.

Tashiro orchid has a typical flower shape for the orchid family, and it also produces fragrance and nectar, so it certainly seems like it would attract insects.

However, a study conducted in Xishuangbanna Dai Autonomous Prefecture, China, found that the only insect that visits this flower is the Asian honeybee , Apis cerana cerana, which is widely distributed in Asia (Zhou et al., 2012).

Moreover, the pollen did not adhere to the bodies of the Eastern honeybees, and therefore did not contribute at all to their fruit production! In other words, although insects visited the Tashiro orchid, it was entirely self-pollinating, producing fruit and seeds. Self-pollination occurred at the bud stage, one day before flowering.

Why are they doing this?

This, too, is likely influenced by its habitat. *Tashiro orchid* grows in very shady forest floors, where insect pollination is virtually impossible. It's possible even bumblebees struggled with pollination.

Therefore, the Tashiro orchid has become self-pollinating, seemingly reaching the ultimate method that surpasses even the Monotropa uniflora and Monotropa uniflora look-alike.

The fragrance and honey are thought to be remnants of their ancestors.

The fruit of the Indian pipe is a berry, and its seeds were dispersed by that disliked creature?

After flowering, Monotropa uniflora produces dull white, fleshy fruits (berries). While this might sound delicious, they are apparently not sweet to humans. The seeds are embedded within the fruit's pulp. Recent research has explored how these seeds are dispersed and how Monotropa uniflora expands its distribution (Uehara & Sugiura, 2017).

We used infrared motion sensors to investigate which insects visit fruit in the wild. As a result, we found that six groups of insects visited: harvestmen, springtails, camel crickets, cockroaches, darkling beetles, and ants. However, only the Japanese cockroach (German cockroach) ingested the seeds. The other species either nibbled on the fruit pulp or visited only in very small numbers. It is natural to conclude that the Japanese cockroach is almost exclusively responsible for dispersing the seeds over long distances.

In this study, to further investigate whether the German cockroach (Erythrina japonica) actually carries the seeds alive, a TTC staining test was conducted to determine if the plants were still alive. This allowed researchers to determine how many seeds survived after being expelled from the cockroach's body.

As a result, approximately half of the seeds survived. Moreover, this result was no different from the survival rate of seeds directly extracted from the fruit by hand, suggesting that they were hardly affected by cockroach digestion.

The activity period of the Japanese cockroach coincides with the fruit-producing period, and since it lives on the ground, it is highly likely to come into contact with the mycelium of the Russulaceae fungi that it parasitizes. Its high flight ability also suggests that it can carry seeds over long distances. It seems to be a very convenient seed carrier for Monotropa uniflora.

However, the Japanese cockroach (Tomioka et al., 2016) is said to have a distribution that extends from the vicinity of Tokyo as far north as various parts of the Pacific Ocean southward, and along the Sea of Japan coast as far south as Ishikawa Prefecture, with its southern limit reaching Tanegashima Island. Although it has now spread as far north as Tochigi Prefecture, it does not exist further north than that. Therefore, it is highly likely that the populations in the Southern Kuril Islands and from northern Japan to Hokkaido are dispersed by other animals.

Based on these circumstances, research was also conducted in Hokkaido, where it was discovered that seed dispersal also occurs through camel crickets, woodlice, and earwigs (Suetsugu et al., 2024).

It seems that Monotropa uniflora is a plant that lives in harmony with many creatures, including fungi, bumblebees, and German cockroaches. When studying this species, it seems necessary to observe it while being aware of its relationships with various living things.

Why are the fruits of Monotropa uniflora capsules?

On the other hand, the fruit of Monotropa uniflora is an erect, oval-spherical capsule, 1-1.5 cm long, which is completely different from the flowers of Monotropa uniflora, which were similar in appearance.

How does Monotropa uniflora disperse its seeds?

A Japanese study that closely observed the morphology of the seeds found that the seed coat extends beyond surrounding the inner milky pulp, forming a wing-like structure, which is thought to allow the seeds to be dispersed by wind (Ugajin & Endo, 2018).

Some people who learn about this might think that capsules are a more primitive characteristic within the Pyrola subfamily. This is because there are many other wind-dispersed plants, and there are no examples of plants relying on cockroaches to eat their fruit. It seems that the evolution occurred from wind-dispersed capsules to cockroach-dispersed berries.

However, similar studies have revealed that the evolution from berries to capsules actually occurred. This can be determined by statistically analyzing the various characteristics of seeds of each species. It was also found that this evolution occurred four times independently.

Why did the evolution from cockroach-dispersed berries to wind-dispersed capsules occur?

Unfortunately, the reason for this is still not well understood. However, in my opinion, there are some possible reasons for this in the case of Japanese Monotropa uniflora and Monotropa uniflora var. japonica.

The fruiting period for Monotropa uniflora is from May to September. Therefore, as mentioned above, this overlaps with the activity period of adult German cockroaches, and it is possible that they will eat the fruit.

On the other hand, since Monotropa uniflora has a later flowering period, its fruiting period is from October to November. By this time, the adult Japanese cockroaches have finished giving birth and are gone. Japanese cockroaches are known to overwinter mainly as sixth-instar larvae (Tomioka et al., 2016). They may need to be of a certain size to eat the fruit and disperse their seeds.

Therefore, the delayed fruiting period may have resulted in wind dispersal. However, this is just a hypothesis, and a comprehensive study of various closely related species would be necessary to determine the actual cause.

References

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

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Source

This article is a significantly expanded version of the one included in the following book.