Both Chinese tallow tree (Toxicodendron sylvaticum) and Japanese wax tree (Toxicodendron succedaneum) are deciduous trees, and both have "haze" in their names. This is because their fruits or seeds contain a large amount of fat and have a history of being used as wax. However, perhaps because of this, Chinese tallow tree and Japanese wax tree are sometimes confused. In reality, Chinese tallow tree and Japanese wax tree have completely different classifications and morphologies. Chinese tallow tree belongs to the Euphorbiaceae family, while Japanese wax tree belongs to the Anacardiaceae family, and differences are evident in their leaves, flowers, and fruits. It is the Japanese wax tree that has been used as a source of traditional Japanese candles. This article will explain the classifications and morphologies of these two species that have "haze" in their names.

What are Chinese tallow trees (Toxicodendron succedaneum) and Japanese wax trees (Toxicodendron succedaneum)?

Chinese tallow tree (Triadica sebifera), also known as the Chinese tallow tree, is native to eastern China and Taiwan, and has been introduced to Japan, the Korean Peninsula, Vietnam, India, the United States, and Puerto Rico. In its native habitat, it is a deciduous tree that grows in valleys and limestone forests (Wu et al., 2008). Globally, it is cultivated for multiple purposes, including wax, medicine, soap, food, paint, timber, and fuel, due to the large amount of oil contained in its seeds. In Japan, it has been used for similar purposes since its introduction during the Edo period, but recently it is mainly used as a street tree or park tree (Hioki et al., 2015). It is also popular as a dried flower. Although it is considered an invasive species in Japan, fossils of the Chinese tallow tree have been unearthed from the Paleo-Lake Biwa Formation in Shiga Prefecture (a geological formation distributed from around Lake Biwa to the hills near Iga City in Mie Prefecture, which was a lake that existed approximately 4 million to 430,000 years ago), so it is technically an extinct species.

Toxicodendron succedaneum, also known as the Japanese wax tree (Toxicodendron succedaneum), is distributed in Honshu (west of the Kanto region), Shikoku, Kyushu, and the Ryukyu Islands in Japan; as well as in China, Taiwan, Malaysia, and India. It is a deciduous tree that has escaped cultivation and become naturalized in warm mountainous areas, especially in coastal regions (Kanagawa Prefecture Flora Survey Association, 2018). Its fruit contains a lot of fat and was used to make Japanese candles, specifically known as "haze wax."

Both are deciduous trees, and both have "haze" in their name. This name comes from the fact that their fruits or seeds contain a large amount of fat and have a history of being used as wax.

However, perhaps due to this history, some people seem to mistakenly believe that the Chinese tallow tree is the same as the Japanese wax tree (Rhus succedanea).

What is the difference between Chinese tallow tree and Japanese wax tree?

While Chinese tallow tree and Japanese wax tree (Rhus succedanea) have somewhat similar names and uses, it's safe to say that they are completely different in other aspects, from classification to morphology.

First, there is a difference in that Chinese tallow tree belongs to the genus Euphorbia in the family Euphorbiaceae, while Japanese wax tree belongs to the genus Rhus in the family Anacardiaceae.

Therefore, there are differences in their basic structure (Kanagawa Prefecture Flora Survey Association, 2018; Mogi et al., 2000).

Regarding the leaves, the Chinese tallow tree has a distinctive rhombic-ovate to broadly ovate shape, while the Japanese wax tree (Rhus succedanea) has odd-pinnately compound leaves.

Both have yellow flowers, but the difference is that Chinese tallow trees produce flowers without petals, while Japanese wax trees produce flowers with five petals that curve backward.

While I mentioned that both fruits contain fat, in reality, Chinese tallow tree has a capsule that ripens to a brown color, splits open, and releases three white seeds. The fat is contained in the aril (the white part of the seed), whereas Japanese wax tree has a drupe that is flattened and does not split open, and the flesh contains a large amount of fat.

Simply put, the fruit of the Chinese tallow tree splits open to release white seeds, but this does not happen with the Japanese wax tree (Rhus succedanea).

From the above, you can see that the two types are completely different.

In terms of use, traditional Japanese candles made in Japan are made from the wax tree (Rhus succedanea), not the Chinese tallow tree (Tallow tree).

Are there any other similar types?

In Japan, the only species of the Chinese tallow tree commonly introduced is the Chinese tallow tree (Tricholoma rhodopolium), so it's rare to have trouble identifying a species.

The genus Rhus, to which the Japanese wax tree (Rhus sylvestris) belongs, also includes other species such as lacquer trees (Rhus verniciflua), Japanese lacquer tree (Rhus alkekengi), and Japanese wax tree (Rhus sylvestris). It is necessary to distinguish the Japanese wax tree from these other species. Please see the separate article for more details.

What are the differences between Japanese wax tree (Rhus sylvestris), Japanese lacquer tree (Rhus trichocarpa), and Japanese lacquer tree (Rhus trichocarpa)? We explain how to distinguish between similar species! Why do they cause rashes? Why was Japanese lacquer tree used as a raw material for Japanese candles? What birds in nature like them? Did autumn foliage play a role?

Japanese wax tree (Rhus sylvestris), Japanese lacquer tree (Rhus trichocarpa), and Japanese lacquer tree (Rhus trichocarpa) all belong to the Rhus genus and are relatively common even in urban areas. They are similar species often seen in gardens and along roadsides, characterized by their odd-pinnately compound leaves. Distinguishing between them is difficult, but careful observation of the leaves is essential. The number of leaflets and the degree of hairiness are major clues...

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How are the seeds dispersed? Why are the fruits so oily? There's a bird that loves fat!?

The oil contained in the white aril that covers the distinctive seeds of the Chinese tallow tree is beneficial to humans, but who in the natural world utilizes it?

Research has shown that these fruits are eaten by birds, which then disperse the seeds.

However, when it comes to fruit, humans tend to prefer sweeter fruits, but why do they have these particular shapes and components?

While this isn't fully understood, it's possible that by altering the composition, nutrients like nitrogen and lipids (which serve as energy sources) are added, differentiating the fruit from those of other plants. This, in turn, may influence the types of birds that prefer it.

A study conducted in a green space park in Osaka Prefecture, Japan, revealed that birds such as the Oriental Turtle Dove, Carrion Crow, Large-billed Crow, Eurasian Tree Sparrow, Oriental Greenfinch, Brown-eared Bulbul, Starling, and Great Tit were eating the seeds (Fukui and Ueda, 1999).

However, turtle doves grind the seeds before eating them, and sparrows, greenfinches, and great tits don't swallow them whole but only peck at the aril, so they don't contribute to seed dispersal.

Therefore, it is believed that at least the carrion crow, jungle crow, brown-eared bulbul, and starling contribute to seed dispersal. Live seeds have actually been found in the droppings of these birds.

Another study conducted at Hiroshima University's Higashi-Hiroshima Campus found that medium-sized birds such as brown-eared bulbuls and thrushes are involved in seed dispersal (Okugawa, 2009).

It should be noted that while there are differences in the fat-containing parts of the fruit of the Japanese wax tree, it is known that the evolution of fat content occurred for exactly the same reasons.

References

Fukui, Nobuyuki & Ueda, Keisuke. 1999. Seed dispersal of the Chinese tallow tree (Sapium sebiferum) by birds. Journal of the Ornithological Society of Japan 47(3): 121-124. https://doi.org/10.3838/jjo.47.121

Hioki, Yoshiyuki; Iwanaga, Fumiko; and Yamamoto, Fukutoshi. 2015. Current status of the invasive alien woody species Amorpha fruticosa L. and Triadica sebifera (L.) Small in Japan. Journal of the Japanese Society of Landscape Architecture 40(3): 472-478. https://doi.org/10.7211/jjsrt.40.472

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

Mogi, Toru; Ota, Kazuo; Katsuyama, Teruo; Takahashi, Hideo; Shirokawa, Shiro; Yoshiyama, Hiroshi; Ishii, Hidemi; Sakio, Hitoshi; and Nakagawa, Shigetoshi. 2000. Flowers Blooming on Trees: Polypetalous Flowers (Vol. 2, 2nd edition). Yama-kei Publishers, Tokyo. 719pp. ISBN: 9784635070041

Okugawa, Yuko. 2009. Escape of the introduced woody plant *Tallow Tree japonica* and its limiting factors. Research Reports of the Hiroshima University Museum 1: 63-70. https://doi.org/10.15027/28722

Wu, ZY, Raven, PH, & Hong, DY (Eds.). 2008. Flora of China (Vol. 11 Oxalidaceae through Aceraceae). Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis. ISBN: 9781930723733

Poinsettias, Euphorbia hederacea, and Euphorbia leucocephala all belong to the Euphorbia genus of the Euphorbiaceae family. While they are widely cultivated for ornamental purposes, they can also become naturalized. Their most distinctive feature is the presence of bright red or white, petal-like "bracts," but this characteristic is common to all three species, which can sometimes lead to confusion. The three species can generally be distinguished by the extent and color of their colored bracts, and the shape of their leaves can also be a helpful indicator. The idea that "poinsettias are poisonous" is circulating on the internet, particularly on the Japanese Wikipedia, but this is a clear hoax, and no toxicity has been confirmed to date. This article will explain the classification, morphology, and toxicity of the Euphorbia genus, which has colored bracts.

What are poinsettias, Euphorbia helioscopia, and false poinsettias?

Euphorbia pulcherrima, also known as poinsettia or Christmas flower, is native to Central America and cultivated as an ornamental plant worldwide, including Japan. It is an evergreen shrub that has escaped cultivation and become naturalized in subtropical to tropical regions (RBG Kew, 2024). In Japan, it is cultivated only for ornamental purposes.

Euphorbia cyathophora, also known as "Scarlet Grass," is native to the Americas (United States to Argentina) and is cultivated as an ornamental plant worldwide, including in Japan. It is an annual plant that has escaped cultivation and become naturalized in subtropical to tropical regions. In Japan, it is widely naturalized in cultivated fields and open fields of the Amami Islands, Daito Islands, Ryukyu Islands, and Ogasawara Islands.

Euphorbia heterophylla, also known as false scarlet grass, is native to Central and South America (Venezuela to Argentina). It is cultivated as an ornamental plant worldwide, including in Japan, and has escaped cultivation and become naturalized in subtropical to tropical regions. In Japan, it has become naturalized in Okinawa.

All of these plants belong to the Euphorbia genus of the Euphorbiaceae family, and while they are widely cultivated for ornamental purposes, they can also become naturalized. In Japan, they are sometimes called "Christmas flowers" because some of them turn a vibrant red or white around November to December, and they are very popular as potted plants.

The most striking feature is the bright red or white, conspicuous parts, but this is often misunderstood as petals. These are not petals, but rather "bracts" or "bract leaves," which are originally leaves that have undergone a special transformation. Flowers do not have petals or sepals.

Other characteristics include large, oval-shaped leaves measuring over 2 cm in width, and the presence of only one or two glands in the cyathium inflorescence.

What are the differences between poinsettia, dwarf poinsettia, and false poinsettia?

The three species are relatively easy to distinguish (Wu et al., 2008; Kanagawa Prefecture Flora Survey Association, 2018).

First, they can be broadly classified into poinsettias and Epipactis thunbergii/Epipactis humilis.

As mentioned above, all three species have leaves called bracts that turn color around the flower during the flowering season. However, in poinsettias, the entire bract is uniformly bright red (white or yellow in some horticultural varieties), whereas in Euphorbia pulcherrima and Euphorbia pulcherrima, only the base of the bract is partially colored red or white.

Also, as its standard Japanese name, "Shojoboku," suggests, poinsettias are woody plants, while Epipactis thunbergii and Epipactis thunbergii are basically herbaceous plants, only partially woody even as they grow.

These two points make it easy to distinguish between them.

Regarding *Eriobotrya japonica* and *Eriobotrya japonica* var. *also known as *Eriobotrya japonica*, the main difference is that *Eriobotrya japonica* has a cornice in the middle of its leaves, and the base of its bracts becomes spotted red during the flowering season, while *Eriobotrya japonica* var. *also known as *Eriobotrya japonica* lacks a cornice in the middle of its leaves, and its bracts do not turn red during the flowering season, although the base of the bracts is somewhat whitish.

However, although it is rarely mentioned in botanical guides for some reason, it seems that the bracts of *Epipactis thunbergii* can also turn white depending on the season. However, even in that case, you should be able to distinguish it from the leaves by the spotted coloring (clearly separated colors) and the overall condition of the leaves.

Beware of the misinformation on Wikipedia that says "poinsettias are poisonous."

The Japanese Wikipedia entry states that "the entire plant contains the toxic compound phorbol esters, which cause dermatitis and blisters. It is not a lethal poison, but there was a reported case in Hawaii in 1919 where a child died after eating a poinsettia." Since the plant releases a milky sap when damaged, it might be thought to be poisonous to humans as well.

However, the English Wikipedia and academic papers state the exact opposite, and it is generally known to be non-toxic (Krenzelok, 1996; Evens & Stellpflug, 2012).

The story began with an urban legend in 1919 about a two-year-old child who died after eating poinsettia leaves, and in 1944, this story was included in a book called "Poisonous Plants of Hawaii."

The author later admitted that this story was hearsay and that poinsettias have never been proven to be poisonous, but the plant continued to be thought to be deadly, with the U.S. Food and Drug Administration issuing a newsletter in 1970 that erroneously stated that "one poinsettia leaf could kill a child," and in 1980 poinsettias were banned in a nursing home in a county in North Carolina.

However, when the American Poison Control Center investigated 22,793 cases of poinsettia exposure, they found that 92.4% did not produce toxicity, and 3.4% only caused mild symptoms.

In a study where rats were orally administered 25 g/kg of poinsettia, no evidence of symptoms was observed during the 14-day observation period, and no toxicity was detected in subsequent autopsies.

From these factors, it can be said that these substances are often harmless to most people.

However, it has been pointed out, though rare, that because it belongs to the same family as Hevea brasiliensis, the raw material for natural rubber latex, and shares two common allergen proteins, there is a possibility that the immune system may malfunction and cause a cross-reaction.

Therefore, it is recommended that people with an allergic reaction to rubber, or those with atopic dermatitis or other systemic atopic conditions, avoid using it.

Furthermore, I would like to add that the long-term effects of continuous consumption are unknown, and since lotions have mostly evolved to protect against some kind of external threat, I would not recommend intentionally consuming them.

References

Evens, ZN, & Stellpflug, SJ 2012. Holiday plants with toxic misconceptions. Western Journal of Emergency Medicine 13(6): 538-542. https://doi.org/10.5811westjem.2012.8.12572

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

Krenzelok, EP, Jacobsen, TD, & Aronis, JM 1996. Poinsettia exposures have good outcomes… just as we thought. The American Journal of Emergency Medicine 14(7): 671-674. https://doi.org/10.1016/S0735-6757(96)90086-8

RBG Kew. 2024. 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/

Wu, ZY, Raven, PH, & Hong, DY (Eds.). 2008. Flora of China (Vol. 11 Oxalidaceae through Aceraceae). Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis. ISBN: 9781930723733

Both Mallotus japonicus and Mallotus japonicus are deciduous trees belonging to the Euphorbiaceae family and share the characteristic of having extrafloral nectaries at the base of their leaves. Therefore, it can be difficult to distinguish between them. Also, the Japanese name "Akamegashiwa" contains the word "kashiwa," which may make you wonder about its relationship to oak. However, oak is a completely different species belonging to the Fagaceae family, so the only commonality is that they were used in the same way. Mallotus japonicus and Mallotus japonicus can be clearly distinguished by differences in the shape and color of various parts of their leaves, such as the presence or absence of stellate hairs. The flowers have no petals, and the male flowers are white. The fruit is a capsule. This article will explain the classification and morphology of Mallotus japonicus and Mallotus japonicus.

What are *Mallotus japonicus* and *Mallotus japonicus*?

Mallotus japonicus, also known as Akamegashiwa (red-budded oak), is a deciduous tree distributed in Honshu (south of Akita Prefecture), Shikoku, Kyushu, and the Ryukyu Islands in Japan, as well as in China. It grows in bright areas such as logging sites, landslide areas, and forest edges (Mogi et al., 2000; Kanagawa Prefecture Flora Survey Association, 2018).

Alchornea davidii, also known as large-leaved red oak, is a deciduous shrub distributed in China, growing in valleys, streams, river slopes, and deciduous forests (Wu et al., 2008). In Japan, it is cultivated somewhat rarely as a garden tree or park tree because of the beauty of its young leaves when it sprouts, and it occasionally grows wild in barren areas, forming colonies (Hayashi, 2019).

All of them are deciduous trees belonging to the Euphorbiaceae family, and they share the common characteristic of having "extrafloral nectaries" at the base of their leaves.

Extrafloral nectaries are glands that secrete nectar in parts of the plant other than the flower itself. They usually secrete nectar as food, attracting ants and driving away parasites (in this case, herbivorous insects) that attach to the plant's body (Yamao & Hata, 2014). Ladybugs can often be seen visiting these nectaries on Mallotus japonicus.

In addition, the leaf shape can be very similar if the margins are entire, which may make identification difficult.

What is the difference between Mallotus japonicus and Quercus dentata?

Since it has the name "Akamegashiwa," some people might be curious about its relationship to "Kashiwa" (oak).

The Japanese name Akamegashiwa is said to originate from the fact that its new shoots are red and that, like the leaves of the oak tree, they were used to hold or wrap food.

However, *Mallotus japonicus* and *Quercus dentata* are completely different species.

Quercus dentata belongs to the genus Quercus in the family Fagaceae, and as mentioned above, it is completely different from Mallotus japonicus, which belongs to the family Mallotustaceae.

Furthermore, while the fruit of the Japanese oak (Quercus acuta) is a type of nut called an acorn, the fruit of the Japanese red oak (Mallotus japonicus) is not.

Furthermore, while oak trees prefer to inhabit high altitudes such as hilly areas and mountainous beech forest zones, making them rarely seen, red oak trees can be frequently found in lowlands.

What are the differences between Mallotus japonicus and Mallotus japonicus?

Many differences can be observed between Mallotus japonicus and Mallotus japonicus.

First, while *Mallotus japonicus* belongs to the genus *Mallotus japonicus*, *Mallotus japonicus* belongs to the genus *Mallotus japonicus*, so it can be expected that there are significant morphological differences.

Specifically, the difference is that *Mallotus japonicus* has stellate hairs (trichomes) on its young branches and leaves, while *Mallotus japonicus* has hairs, but lacks stellate hairs on its young branches and leaves. It's a little hard to see, but the brown hairs on the veins and petioles of *Mallotus japonicus* are the stellate hairs.

Furthermore, the hairs (trichomes) on the surface of Mallotus japonicus are thought to be a physical defense trait against herbivorous insects, and on the underside of the leaves, there are capsule-like structures called glandular dots containing secondary metabolites, which are known to function as a chemical defense trait (Yamao and Hata, 2014).

Furthermore, while Mallotus japonicus has both undivided and divided leaves (leaves with incisions), Mallotus japonicus has only undivided leaves and no divided leaves.

The base of the leaf blade is wedge-shaped to truncate in Mallotus japonicus, while it is heart-shaped in Mallotus japonicus.

The petioles are red in Mallotus japonicus, but green in Mallotus japonicus.

Both species have a pair of extrafloral nectaries at the base of the leaf blade. In Mallotus japonicus, the entire nectary is red and no other special structures are visible, whereas in Mallotus japonicus, the entire nectary is green and a linear appendage can be seen below the nectary.

This should allow you to distinguish them reliably.

What is the structure of a flower?

The flowers are small and inconspicuous, as is common in the Euphorbiaceae family, and the distinction between petals and sepals is unclear.

Mallotus japonicus flowers from June to July. It is dioecious (having separate male and female plants). It produces conical inflorescences 7-20 cm long at the tips of its branches. The flowers have no petals. Male flowers grow in clusters of several in the axils of the bracts, and the calyx is pale yellow and 3-4 lobed. There are numerous stamens, and the filaments are about 3 mm long. Female flowers grow singly in the axils of the bracts, and the calyx is 2-3 lobed. The ovary has spine-like projections and is covered with reddish stellate hairs and white glandular dots. There are 3-4 styles, densely covered with papillary projections. The papillary projections are initially reddish and turn yellow when mature.

Ooba-benigashiwa (Ooba-benigashiwa) flowers from April to May. It is dioecious (having separate male and female plants). Male inflorescences have 1 to 3 flowers per leafless node, are unbranched, catkin-like, and 1.5 to 3.5 cm long. Male flowers have 3 to 5 flowers per bract, with pedicels about 2 mm long, spherical buds about 2 mm in diameter, glossy, 3 (or 4) sepals, and 6 to 8 stamens. Female inflorescences are terminal, unbranched, 4 to 8 cm long, glossy, with triangular bracts about 3.5 mm long. Female flowers have pedicels about 0.5 mm long, 5 triangular sepals 2.5 to 3 mm long, glossy, a subglobose ovary with cottony hairs, and 3 filiform styles 10 to 12 mm long, fused together at 1.5 to 2 mm.

How did they pollinate? They used both wind and bumblebees!?

As can be seen from its small, inconspicuous flowers, Mallotus japonicus relies on wind for pollination (Yonebayashi, 2023).

However, it has also been found that some special types of bees, such as the yellow-breasted bumblebee, perform a pollination method called buzz pollination, in which they extract pollen through fine vibrations, causing the pollen to be dispersed into the air and resulting in pollination (Ichikawa et al., 2011). In Japan, the yellow-breasted bumblebee is the only insect that has been confirmed to visit these flowers. This is a type of parasitic pollination called buzz and airborne pollination.

What is the structure of the fruit?

The fruit is a capsule, which is common to all plants in the Euphorbiaceae family.

The capsules of Mallotus japonicus are oblate and spherical, about 8 mm in diameter, densely covered with spine-like projections, and ripen to a brown color in September and October. When ripe, they split into 3-4 sections, releasing 3-4 seeds. The seeds are oblate and spherical, about 4 mm in diameter, and black in color.

The capsules of Quercus glauca are subglobose, three-lobed, 10-12 mm in size, and densely covered with downy hairs. The seeds are ovate, about 6 mm in size, brown or gray, and form a head.

How do they disperse their seeds? They're incredibly popular with various birds!?

Although Mallotus japonicus has a capsule fruit, its seeds are dispersed by animal feeding (Sato and Sakai, 2005). After the fruit splits open, the exposed seeds are eaten by birds, and the seeds are dispersed through their droppings.

Specifically, there are records of it being eaten by various birds such as the carrion crow, jungle crow, Okinawa woodpecker, pheasant, turtle dove, Daurian redstart, starling, common starling, and azure-winged magpie, suggesting it is quite popular. In coniferous plantations, it is foraged by nine species, with four species of flycatchers—the Asian brown flycatcher, dark-skinned flycatcher, narcissus flycatcher, and blue-and-white flycatcher—accounting for 751 TP3T.

We see young trees scattered throughout urban areas and forests, which is likely closely related to their popularity among birds.

References

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

Ichikawa, S., Kurahashi, T., & Ikuru, S. 2011. Possibility of a novel pollination mode by flower-visiting bees and yellow-breasted bumblebees collected in Kagawa Prefecture. Bulletin of the Faculty of Agriculture, Kagawa University 63(116): 43-59. ISSN: 0368-5128, http://id.nii.ac.jp/1731/00003553/

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

Mogi, T., Ota, K., Katsuyama, T., Takahashi, H., Shirokawa, S., Yoshiyama, K., Ishii, E., Sakio, H., and Nakagawa, S. 2000. Flowers Blooming on Trees: Polypetalous Flowers (Vol. 2, 2nd edition). Yama-kei Publishers, Tokyo. 719pp. ISBN: 9784635070041

Sato, Shigeho & Sakai, Atsushi. 2005. Birds as seed dispersers of Mallotus japonicus in coniferous plantations. Journal of the Ornithological Society of Japan 54(1): 23-28. https://doi.org/10.3838/jjo.54.23

Wu, ZY, Raven, PH, & Hong, DY (Eds.). 2008. Flora of China (Vol. 11 Oxalidaceae through Aceraceae). Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis. ISBN: 9781930723733

Yamao, Ryo & Hada, Yoshio. 2014. Variation in predation defense traits of Mallotus japonicus in response to heterogeneity of soil nutrients and moisture on slopes, and leaf utilization by insects. Konchu New Series 17(3): 111-118. https://doi.org/10.20848/kontyu.17.3_111

Yonebayashi, Naka. 2023. Airborne pollen count over a five-year period (2017-2021) in the suburbs of Kumagaya City. Global Environmental Research 25: 1-13. ISSN: 1344-9842, http://ris-geo.jp/wp/wp-content/uploads/2023/05/25_02_Yonebayashi.pdf

The Daphniphyllaceae family consists of evergreen trees or shrubs. The leaves are densely arranged alternately at the tips of branches, narrowly oblong with entire margins. The flowers are unisexual and dioecious, arranged in axillary racemes. They lack petals, have 3-6 sepals, and 6-12 stamens. Because they have 2 carpels instead of 3, they were separated from the Euphorbiaceae family. The fruit is a drupe containing one seed. There are 30 species in this genus worldwide, with 2 species found in Japan.

This article provides a comprehensive, field guide-style introduction to plants belonging to the Daphniphyllaceae family.

The photos are replaced as soon as better ones are taken. Also, while the identification is done by the author, please note that if there are any misidentifications, they may be changed without notice.

No.1349 Daphniphyllum macropodum subsp. macropodum

This is an evergreen tree (a tree with flowers). The bark is grayish-brown with vertical stripes and oval lenticels. Young branches are reddish in color. Older branches have prominent leaf scars. The leaves are alternate, clustered in whorls at the tips of the branches. The leaf blade is oblong to oblanceolate, 8-20 cm long and 3-7 cm wide. The tip is short and pointed, and the base is wedge-shaped. The margin is entire. There are 10-19 pairs of lateral veins. The leaves are leathery and glabrous on both sides. The upper surface is glossy, and the underside is whitish. The petiole is 3-6 cm long and often reddish. The flowering period is from May to June. Racemes 4-12 cm long emerge from the leaf axils of the previous year's branches. Male flowers lack petals and sepals, and have 6-12 stamens. The filaments are free, and the brownish-purple anthers are conspicuous. The female flowers have small or absent sepals. The ovary is narrowly ovate, 1-2 mm long. The stigma is brownish-purple, with 2-4 segments curving outwards. The fruit is a drupe, 8-9 mm long, ovate-elliptic, ripening to a bluish-black color in November-December, with a powdery surface. The style is persistent. The terminal bud of the winter bud is narrowly ovate, tinged with red, and enclosed in numerous bud scales that are modified petioles. The leaf scar is obovate and large, with three vascular bundle scars. Flowering branches have inflorescence branch scars. The small, round buds in the leaf axils are flower buds. It is distributed in Honshu (west of Fukushima Prefecture), Shikoku, Kyushu, the Ryukyu Islands, Korea, and China. It grows in warm-climate evergreen forests. Because the old leaves fall after the new leaves emerge, it is called "yuzuri-ba" (yuzuri leaves), likened to a parent yielding to its offspring after it has grown (Kanagawa Prefecture Flora Survey Association, 2018). It is sometimes cultivated for ornamental purposes and is used in New Year's decorations. Pollination is carried out by bees (superfamily Apoidea, order Diptera, family Scarabaeidae) (Yumoto, 1988), and seeds are dispersed by birds (Kominami, 1999).

No. 1350 Daphniphyllum macropodum subsp. humile

This subspecies of Daphniphyllum macropodum, which is distributed in warm regions on the Pacific side of Japan, has adapted to the heavy snowfall areas on the Sea of Japan side of Honshu (Satake, 1999). It is an evergreen shrub. It is dioecious. It grows to a height of 1-3m, and its branches are flexible and resistant to breakage. The leaves are alternate on the branches, with petioles 3-5cm long. The leaves are elliptic to obovate-oblong in shape, 9-20cm long and 5-6cm wide, with a rounded or wedge-shaped base and a short, pointed tip. The leaf margins are entire, the upper surface is glossy, and the underside is slightly greenish-white. It flowers from May to June, and the flowers lack a perianth, with racemes emerging from the leaf axils. It bears oval fruits with long pedicels from October to November. It can be distinguished from Daphniphyllum macropodum by its curved trunk, which makes it a shrub-like tree 1-2m tall, and its leaf length of 10-17cm. It is distributed along the Sea of Japan coast of Hokkaido and the central and northern parts of Honshu, and grows naturally on the forest floor in areas with heavy snowfall. It is found on the forest floor of beech forests and other areas, along with evergreen creeping plants that are characteristic of the Sea of Japan, such as Camellia japonica, Ilex crenata, Aucuba japonica, Skimmia japonica, and Taxus cuspidata (Fukushima, 2017).

No. 1351 Daphniphyllum teijsmannii

This evergreen tree (a tree with flowers) grows in evergreen broad-leaved forests from southern Tohoku to Okinawa. It reaches a height of about 10 meters. The bark is grayish-brown with scattered lenticels. Young branches are green, while older branches have noticeable leaf scars. The leaves are alternate and clustered at the tips of the branches. The leaf blade is 4-15 cm long and 2-6 cm wide, narrowly elliptic to oblanceolate, with an entire margin. There are 8-10 pairs of lateral veins, and the reticulate venation is clearly visible. The leaves are leathery, glossy on the surface, and hairless on both sides. The petiole is 1.5-5 cm long, usually green, rarely tinged with red. It is dioecious (having separate male and female plants). Racemes 1.5-6 cm long emerge from the leaf axils of the previous year's branches. The flowering period is from May to June. The flowers tend to cluster at the top of the inflorescence branches. Male flowers have stalks about 3 mm long, lack petals, and have 3-6 small sepals and 4-12 stamens. Female flowers have 3-6 small sepals about 0.5 mm long. The ovary is narrowly ovate, 1-1.5 mm long. The stigma has 3-4 segments, is pale yellow, and curves outward. The fruit is a drupe, elliptical, 8-9 mm long, and ripens to a bluish-black color in December-January. The surface is powdery. The inflorescence does not droop. The stone is 6-7 mm in diameter. The terminal bud of the winter bud is narrowly ovate and enclosed by numerous bud scales that are modified petioles. The leaf scar is large, with 3 vascular bundle scars. Small flower buds are borne in the leaf axils. This species can be distinguished from Daphniphyllum macropodum by its relatively small leaves, 8 to 10 pairs of lateral veins, and reticulate venation visible when held up to the light. Even if not visible through the light, the presence of prominent reticulate venation in a specimen indicates this species. It is distributed in Honshu (west of Fukushima Prefecture), Shikoku, Kyushu, and the Ryukyu Islands. It grows near the coast and is sometimes planted in parks and along streets.

References

Fukushima, Tsutomu. 2017. Illustrated Guide to Japanese Vegetation (2nd edition). Asakura Shoten, Tokyo. 186pp. ISBN: 9784254171631

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

Kominami, Yosuke. 1999. Spatial distribution of seeds carried by birds. In: Ueda, Keisuke (Ed.), Seed Dispersal: The Evolution of Mutual Aid Vol. 1 Seeds Carried by Birds (pp. 17-25). Tsukiji Shokan. ISBN: 9784806711926

Satake, Yoshisuke. 1999. Wild Plants of Japan (New Edition, Woody Plants 1). Heibonsha, Tokyo. 321pp. ISBN: 9784582535044

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

The castor bean plant, said to originate in northeastern Africa, is a perennial plant cultivated worldwide for commercial and ornamental purposes, and sometimes naturalized. It is almost impossible to mistake it for anything else. Its seeds, called "himashi," are rich in oil, and the extracted "castor oil" is highly valued for its diverse uses in cosmetics, shampoos, soaps, hand lotions, laxatives, lamp fuel, and highway lubricants. Its history dates back to around 1550 BC in Egyptian papyrus, and may go even further. Originally used medicinally for treating dermatitis and as a laxative, castor oil has gained attention in modern times as heavy chemical industries have advanced, and it supports our lives in countless ways. On the other hand, the seeds contain toxic components, mainly ricin, and have been misused for military and bioterrorism purposes since the World Wars. While the lethal dose of ricin from inhalation or injection is extremely low at approximately 5-10 μg/kg, the lethal dose from oral ingestion is estimated to be much higher at approximately 1-20 mg of ricin per kg of body weight. This is equivalent to about 8 seeds for an adult. Although ricin alone is extremely dangerous, because ricin is a protein, it is sensitive to heat and denatures, so it is not found in processed castor oil. Oral ingestion weakens its toxicity, and it is also difficult to store, so it may be considered somewhat overhyped. The castor bean flower has an unusual shape, with female flowers at the top and male flowers at the bottom. This is an adaptation for wind pollination, but recent research has shown that it is not only wind pollination but also insect pollination by honeybees promotes increased yield. The fruit also bursts open when dry, scattering the seeds, but it has also been found that elaiosomes attached to the seeds allow ants to carry them far away. This article will explain the classification, history, uses, medicinal uses, toxicity, pollination ecology, and seed dispersal of the castor bean.

A perennial plant native to Africa, cultivated for oil production.

Castor bean (Ricinus communis), also known as castor bean, is a perennial plant originally from northeastern Africa (although there are various theories about its origin, including India), and is cultivated worldwide for oil production and ornamental purposes, and sometimes becomes naturalized (Shimizu et al., 2001). In Japan, it was introduced from Tang (China) and has now escaped cultivation and become naturalized, mainly in western Japan.

The Japanese name "Tougoma" (meaning "castor bean") originates from its introduction from China, and comes from the fact that, like sesame (goma), oil is obtained from its seeds.

The plant is entirely hairless and usually tinged with dark purple. The stem is cylindrical, erect, and sparsely branched, reaching a height of 2 meters. The leaves are large, palmately divided into 5 to 11 lobes, with serrated edges, and arranged alternately on long petioles.

The plant possesses extrafloral nectaries at the base of the petiole and inflorescence axis, attracting ants and providing them with food in exchange for them protecting the plant (Sasidharan & Venkatesan, 2019).

Castor bean belongs to the genus *Ricinus* in the family Euphorbiaceae. The genus *Ricinus* contains no other species, and no closely related or similar species are known. The closest relative would be sesame (*Sesamum indicum*) in the family Pedagoaceae, but other than the oil being extracted from the seeds, there are absolutely no similarities.

What is the history of castor beans? From medicinal use to oil production.

The reason why castor beans are considered important is that their seeds, called "himashi," are rich in oil, and the extracted "castor oil" has a wide range of uses, including cosmetics, shampoos, soaps, hand lotions, laxatives, lamp fuel, and high-speed lubricants (Rizzardo et al., 2012).

On the other hand, because it contains a highly toxic protein called "ricin," it is sometimes used in bioterrorism attacks and is known to become a politically charged incident (Uzawa, 2005).

Historically, the first appearance of castor bean is thought to be in the Ebers Papyrus, the oldest papyrus written in the New Kingdom of Egypt around 1550 BC, which describes ancient Egyptian medicine (Franke et al, 2019). Since the contents of the Ebers Papyrus are thought to be a copy of a text from the Predynastic period of Egypt, predating around 3400 BC, it is possible that castor bean was known even before that time.

Interestingly, in the Ebers Papyrus, it is treated as a medicinal plant for curing diseases, which is somewhat different from its main uses today. It is said that a mixture of the root and water was used for head ailments, a mixture of crushed cantaloupe seeds and beer for expelling intestinal contents, a mixture of ground cantaloupe seeds and oil for hair growth, cantaloupe oil for dermatitis, and a mixture of ground cantaloupe seeds and honey for pain relief. Furthermore, in the 4th century BC, during the late Egyptian dynasty, it was used as currency and as a burial item, signifying that medicine was being offered to the deceased.

Furthermore, the castor bean also appears in the Book of Jonah, one of the Old Testament texts, which is set in the Northern Kingdom of Israel. The exact year of the composition of the Book of Jonah is unknown, but it is thought to be sometime between the late 5th century BC and the early 4th century BC, when the Babylonian exile occurred. Within the Book of Jonah, there is only a description of the rapid growth of the castor bean and the insects that eat it.

In China, the first known formula for castor bean paste was found in the "Bù Qué Zhū Hǎi Yǎi Yǎn" (Bù Qué Zhū Hǎo Bài Yǎi Fàng) revised by Tao Hongjing, a physician and scientist, during the Northern and Southern Dynasties period, specifically the Six Dynasties period (around 500 AD). It also appears in the "Xīn Xiū Ben Cao" (Xīn Xiū Ben Cao), a herbal medicine book revised by Li Ji and others in 659 AD by order of Emperor Gaozong, the third emperor of the Tang Dynasty.

As heavy and chemical industries advanced in modern times, castor oil, with its high viscosity and oily properties, attracted attention as a lubricant. While it continued to be used medicinally in traditional medicine, its commercial uses changed dramatically.

After its widespread adoption in aviation engines in Europe in 1909, it was used as a lubricant in rotary engines such as the Gnome engine. However, due to the increasing power output of engines and its lack of stability against heat and oxidation, by the time of World War II, mineral oil-based lubricants, such as Pennsylvania engine oil, had become the mainstay of aircraft lubricants.

In modern times, its uses have expanded to include food additives, preservatives, soap, waste tempura oil treatment agents (solidifiers), lubricants, hydraulic fluids, paints, inks, waxes, low-temperature resistant resins, nylon, pharmaceuticals, perfumes, and hair oils (pomades, hair styling oils). It is also an important raw material for sebacic acid.

Polyamide 11, which Arkema has been manufacturing and selling for over 50 years, is also derived from castor oil (Miyaho, 2013). In addition to its basic properties, it has excellent flexibility and processability, so it is widely used in extrusion processing applications such as automotive fuel system tubes, air brake tubes, offshore oil drilling pipes, and powder coatings for dishwashers.

Furthermore, lysine is attracting attention for its potential in tumor treatment, including as an anticancer drug (Franke et al., 2019).

What was the incident involving castor beans?

While there are practical uses like these, there are also known instances of the highly toxic ricin contained in castor bean seeds being misused.

During World War I and World War II, the United States and other countries investigated the potential military use of ricin as a biological weapon, such as bullets, shrapnel, or aerosols, although it is believed that it was never actually used (Franke et al., 2019).

After the Cold War began, cases of its actual use in assassinations became known.

In 1978, anti-communist exiles from the People's Republic of Bulgaria were assassinated or nearly assassinated by the Soviet KGB or the Bulgarian Secret Police (STB) by being stabbed with the tip of an umbrella loaded with a bullet containing ricin.

In the United States, there have been several incidents, all unsuccessful, where ricin was sent by mail with the intent of assassination. Barack Obama (44th President) and Donald Trump (45th and 47th Presidents) were among those targeted. Similar incidents are known to have occurred in the Czech Republic and the Federal Republic of Germany.

In Japan, there have been known cases such as in 2015 when a wife attempted to kill her estranged husband by mixing ricin extracted from castor beans into his shochu (Japanese distilled spirit), and in 2021 when a colleague put ricin extracted from castor beans into a water bottle, rendering it unusable. However, there have been no reported deaths.

The production of ricin is prohibited under the Biological Weapons Convention (1972) and the Chemical Weapons Convention (1997) because it can be used as a biological or chemical weapon. However, because it is relatively easy for individuals to produce, such terrorist attacks continue unabated (Franke et al., 2019).

How toxic are castor beans? What is the lethal dose?

What are the toxicity levels of castor beans?

The most prominent toxic component is lysine, a type of lectin (carbohydrate-binding protein) that has already been mentioned (Franke et al, 2019). This is different from lysine, an α-amino acid that is widely used as a supplement worldwide.

The lethal dose of ricin from inhalation and intramuscular/intravenous injection in humans is estimated to be around 5-10 μg/kg, although this is based on various theories as actual experiments cannot be conducted. For a 70kg adult, this would be equivalent to 350-700 μg.

Furthermore, analysis of poisoning cases suggests that the lethal dose of ricin for humans from oral ingestion is approximately 1 to 20 mg per kg of body weight, which is equivalent to about 8 seeds in an adult. In reports documenting clinical symptoms (from mild to fatal), the number of seeds ingested ranged from 0.5 to 30.

Symptoms include hematemesis (vomiting blood), diarrhea, hemorrhagic necrosis of the intestinal wall and myocardium, kidney disease, and circulatory collapse. This effect occurs because lysine inhibits the synthesis of cellular proteins.

Due to its potent toxicity, ricin is known as one of the five most toxic substances, along with tetanus toxin, botulinum toxin, diphtheria toxin, and gramicidin.

It is speculated that its potent toxicity may function as a defense against herbivorous animals in nature. However, the specific animals it evolved to target are still unknown.

Castor beans also contain several other toxic components.

Castor bean agglutinins, unlike lysine, are not cytotoxic, but they do exhibit affinity for red blood cells, causing agglutination and subsequent hemolysis. However, because they are not adequately absorbed from the intestines, their effects are limited to intravenous administration.

Ricinine is an alkaloid toxin found in small amounts in all parts of the plant, including leaves and fruit peels. The median lethal dose for mice is 3 g/kg when ingested orally and 340 mg/kg when administered intraperitoneally. This component is known to act as a repellent or toxin against insects such as the brown leafcutter ant (Atta sexdens rubropilosa) and the fall armyworm (Spodoptera frugiperda).

Why are they used even though they are poisonous? Why is it sometimes okay to ingest them orally?

After hearing all this, you might wonder why zebo oil, which is supposed to be toxic, is used in everyday tools. Why is it usable despite being poisonous?

The reason is that ricin is a protein, and therefore it denatures when heated. During the process of extracting oil from the seeds, the ricin is heated and denatured, so commercially available castor oil products are rendered non-toxic (Saito, 2021). Therefore, they can be used safely.

However, even considering all that, there are still mysteries surrounding ricin. Despite its high toxicity, there are a great many cases where assassination attempts have been unsuccessful. Why is that?

While some of these incidents have certainly been prevented by human intervention, the fact that ricin is a protein is also a contributing factor (Saito, 2021; Kurare & Pharmacology Research Lab, 2022). Because ricin is a protein, it is believed that a certain amount, though not all, is digested in the stomach. In fact, the lethal dose to humans is clearly higher from oral ingestion than from inhalation or intramuscular/intravenous injection. It also has poor shelf life and requires freezing.

Therefore, considering its actual toxicity, it could be said that some aspects have been slightly exaggerated. Nevertheless, it remains dangerous, and its misuse must never be tolerated.

What is the structure of a castor bean flower?

While the seeds of the castor bean plant are often emphasized, its flowers may be less well known. It flowers from June to September, blooming in autumn in Japan. It produces inflorescences about 20 cm long at the top of the stem and in the leaf axils, with female flowers at the top and male flowers at the bottom (Shimizu et al., 2001; Wu et al., 2008).

The female flowers are bright red, with pedicels 5-10 mm long and ovate sepals 4-5 mm long. The ovary is densely covered with slender, cylindrical projections with bristles at the tip. The style is red or orange-red, 4-5 mm long. The stigma widens at the top.

The male flowers are white, with pedicels 5-17 mm long. The sepals are ovate, 5-8 mm long. The stamens are 7-8 mm long.

The contrasting and vibrant colors of the male and female flowers make it understandable why this plant is also valued from an ornamental standpoint.

Flowers can be pollinated not only by wind but also by insects!?

Castor bean flowers can self-pollinate, but they also undergo cross-pollination (Rizzardo et al., 2012). Castor bean flowers have a rather unusual shape, but how do they disperse their pollen?

Until very recently, it was believed that this flower relied solely on wind for pollination, resulting in cross-pollination. Male flowers burst open during blooming, releasing pollen into the wind (Rizzardo et al., 2012). The fact that female flowers are located above and male flowers below is thought to make self-pollination less likely when pollen is carried by the wind.

But it has quite a striking color, even though it doesn't need to attract insects, doesn't it?

A 2012 Brazilian study provided more detailed information (Rizzardo et al., 2012). This study found that the presence of the European honeybee Apis mellifera increased fruit set and seed yield.

This is thought to be due not only to pollination occurring directly as a result of European honeybees seeking pollen and nectar outside the flowers, but also to the fact that the European honeybees stimulated the male flowers, causing many of them to burst open.

Interestingly, it's noteworthy that when European honeybees moved up and down on the same individual flower, they promoted "self-pollination" or "neighboring flower pollination" rather than cross-pollination.

Although not mentioned in this paper, the color of the flower may also be important to insects. It can be said that this is an unusual flower that coexists with both wind and insects. The presence of insects was essential for the increased production of castor bean.

The fruit is a capsule, and the seeds are dispersed both automatically and by ants!?

The fruit is a capsule, dark red, oval or ovate, 1.5–2.5 cm long, covered with spines, which are about 5 mm long or less (Wu et al., 2008). The fruit consists of three carpels and three seeds. The seeds are oval, 7–12 mm long, glossy, gray to silver to beige in color, with dark markings. These seeds are called "castor seeds" and are the raw material for castor oil. The seeds have an appendage called a caruncle, which is a flattened cone shape, 2–3 mm wide.

The seed, or cinnamon seed, can be easily separated into a fibrous "cocole (seed coat)" and a part called the "kernel" (Yasuda and Miyaho, 2010). Furthermore, the kernel is divided into the "embryo," which is the main part that will sprout, and the "endosperm," which contains oil and protein and nourishes the embryo. The endosperm contains 47-51% oil. Approximately 90% of this oil is ricinoleic acid triglyceride.

The seeds are dispersed automatically, and the fruit is known to burst open when dry, scattering the seeds it contains.

However, this is not the only way castor beans disperse their seeds. The seeds have an appendage called a seed cushion. The seed cushion is an appendage derived from the integument at the tip of the seed (near the micropyle). It has been found that this seed cushion is eaten by ants. In other words, it functions as an "elaiosome" (Martins et al., 2006; Sasidharan & Venkatesan, 2019).

Seed pillows are rich in fatty acids and sugars, with the fatty acids (93.4–99%) being palmitic acid, oleic acid, linoleic acid, stearic acid, myristic acid, and palmitoleic acid. Analysis has revealed that they mainly contain glucose, rhamnose, ribose, sucrose, and trehalose, and sugar alcohols mainly consisting of myo-inositol, glycerol, mannitol, and arabitol (Sasidharan & Venkatesan, 2019). These make good food for ants.

When ants approach castor bean seeds, they react to the seed cushion and carry the seeds back to their nest. Only the seed cushion is used as food by the ants; the seeds themselves are inedible and are discarded around the nest. In this way, castor bean seeds are not only dispersed automatically, but also dispersed by ants.

In a study in Brazil, 20 different ant species were identified as being attracted to the site, with Pheidole and Solenopsis species being particularly favored (Martins et al., 2006).

Furthermore, a study in India identified six species: Leptogenys processionalis, Monomorium indicum, Pheidole grayi, Solenopsis geminata, Camponotus compressus, and Aphaenogaster beccarii. However, only two species—Pheidole grayi and Aphaenogaster beccarii —not only ate the food on the spot but also carried it back to their nests at a high rate (Sasidharan & Venkatesan, 2019).

This result suggests that not just any type of ant will visit the elaiosome.

Looking at it this way, it becomes clear that this plant is surprisingly dependent on insects, including its flowers and extrafloral nectaries. Although it has become naturalized in Japan, no research has been conducted from this perspective. If we could find out what kinds of insects it is related to in Japan, we might be able to uncover the secret behind its naturalization.

References

Franke, H., Scholl, R., & Aigner, A. 2019. Ricin and Ricinus communis in pharmacology and toxicology-from ancient use and “Papyrus Ebers” to modern perspectives and “poisonous plant of the year 2018”. Naunyn-Schmiedeberg's Archives of Pharmacology 392: 1181-1208. https://doi.org/10.1007/s00210-019-01691-6

Kurare & Pharmacology Research Lab. 2022. The Unbelievable Dictionary of Toxicology. Sansai Books, Tokyo. 205pp. ISBN: 9784866733067

Martins, F., Guimarães, PR, Silva, RR, & Semir, J. 2006. Secondary Seed Dispersal by Ants of Ricinus communis (Euphorbiaceae) in the Atlantic Forest in Southeastern Brazil: Influence on Seed Germination. Sociobiology 47(1): 265-274. https://guimaraes.bio.br/013.pdf

Miyaho, Jun. 2013. Latest trends and application developments of castor oil-derived polyamides. Journal of the Japan Rubber Association 86(6): 188-193. https://doi.org/10.2324/gomu.86.188

Rizzardo, RA, Milfont, MO, Silva, E., & Freitas, BM 2012. Apis mellifera pollination improves agronomic productivity of anemophilous castor bean (Ricinus communis). Anais da Academia Brasileira de Ciências 84: 1137-1145. ISSN: 0001-3765, https://doi.org/10.1590/S0001-37652012005000057

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

Sasidharan, R., & Venkatesan, R. 2019. Seed elaiosome mediates dispersal by ants and impacts germination in Ricinus communis. Frontiers in Ecology and Evolution 7: 246. https://doi.org/10.3389/fevo.2019.00246

Shimizu, K., Morita, H., & Hirota, S. 2001. Illustrated Guide to Naturalized Plants of Japan: 600 Species of Plant Invaders (Revised). National Rural Education Association, Tokyo. 553pp. ISBN: 9784881370858

Uzawa, Hirotaka. 2005. Ultra-high sensitivity detection technology for highly toxic ricin: Enabling detection of 1/10,000th of the lethal dose in just 10 minutes. AIST Today 5(12): 16-19. ISSN: 1880-0041, https://www.aist.go.jp/Portals/0/resource_images/aist_j/aistinfo/aist_today/vol05_12/vol05_12_p16_19.pdf

Yasuda, Maho & Miyaho, Jun. 2010. Polyamides made from castor oil. Journal of the Textile Society of Japan 66(4): 137-142. https://doi.org/10.2115/fiber.66.P_137

Wu, ZY, Raven, PH, & Hong, DY (Eds.). 2008. Flora of China (Vol. 11 Oxalidaceae through Aceraceae). Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis. ISBN: 9781930723733

Enokigusa is a common species found on roadsides and in fields in flat areas, but if you're not familiar with it, you might get confused with the hackberry tree (Enoki), as its name suggests. While there are similarities such as leaf veins, serrations, and pointed tips, their classifications are fundamentally different, with a major difference being whether they are herbaceous or woody plants. Their flowers and fruits are also completely different. The leaves are similar, but upon closer inspection, their shape and sheen are different. Two varieties of Enokigusa have been identified: velvet Enokigusa and long-leaved Enokigusa. They are distinguished by the shape of their leaves and the amount of hairiness, but the differences are continuous and not always distinguishable. Enokigusa has unique flowers, and self-pollination occurs when its male flowers fall to the ground and are received by its female flowers in a basket-like bract. This can be found with a little research, but it also seems that wind pollination occurs. Considering all of this together, the reason why Enokigusa uses such a roundabout method of self-pollination may become clear. The fruit is a capsule, and the seeds are dispersed by ants. This article will explain the classification, pollination ecology, and seed dispersal of *Celtis sinensis*.

Enokigusa, a plant that grows on roadsides and in fields in flat areas and resembles the leaves of the hackberry tree.

Acalypha australis, also known as hackberry grass, is distributed in Hokkaido, Honshu, Shikoku, Kyushu, and the Ryukyu Islands in Japan; as well as in China, South Korea, Laos, the Philippines, eastern Russia, and Vietnam. It has naturalized in northern Australia and eastern India. It is an annual plant that grows along roadsides and in fields in lowland areas (Satake, 1999).

It belongs to the genus Acalypha in the family Euphorbiaceae. Other known species in the genus include the naturalized species Acalypha ostryifolia and the cultivated species Acalypha hispida and Acalypha hispaniolae, but all of them are rarely seen in the wild, and their flower forms differ greatly, so there is no confusion between the species.

However, as its name suggests, it is sometimes compared to Celtis sinensis, a completely different species belonging to the Cannabaceae family. The leaf veins, serrations, and pointed tips are similar, so it may be difficult to distinguish between them at first.

The Japanese hackberry (Enoki) is a deciduous tree distributed in Honshu, Shikoku, and Kyushu in Japan; as well as in Korea and China. It grows in sunny, moderately moist areas from hills to mountains, and along coastal areas.

Although it is a large deciduous tree, the fruits of wild and cultivated individuals are eaten by birds, and the seeds are dispersed. As a result, young trees can grow even in small green spaces in urban areas, and these young trees can sometimes be found in the same places as hackberry, which may cause confusion.

You can distinguish between hackberry grass and hackberry by the stiffness of their branches and the shape of their leaves.

However, there are significant differences between *Celtis sinensis* and *Celtis sinensis* (Hayashi et al., 2013).

The biggest difference, as mentioned above, is that hackberry is an annual plant, while hackberry is a deciduous tree. Therefore, they are clearly distinguishable in large specimens, and even large hackberry plants have soft stems, while hackberry plants have hard, firm stems even in young trees.

Although the leaves are very similar, those of *Celtis sinensis* are nearly bilaterally symmetrical, oblong to broadly lanceolate, with fine serrations and a slight sheen, while those of *Celtis sinensis* are nearly bilaterally asymmetrical, broadly elliptic, with sparse serrations and no sheen.

In addition, mature hackberry trees have small, wavy, blunt serrations on the upper third of their leaves, but some have entire margins, and young trees have blunt serrations almost to the base. The extent of blunt serrations also varies in hackberry grass, so this point may not be relevant.

The flowers and fruits are completely different. In hackberry, the inflorescence is located in the leaf axils, with small male flowers arranged in a spike at the top and female flowers enclosed in a conical involucre at the base, a form that doesn't immediately resemble a flower. The fruit is a drupe, spherical in shape and about 6 mm in diameter, whereas in Japanese hackberry, the perianth has four segments, resembling a typical flower, and the fruit is a capsule, spherical in shape and about 3 mm in diameter.

For other species similar to hackberry, please see our separate article.

What are the differences between Japanese hackberry (Enoki), Japanese hackberry (Ezoensis), and Chinese hackberry (Mukunoki)? An explanation of how to distinguish between similar species.

Japanese hackberry (Enoki), Japanese hackberry (Ezoensis), and Chinese zelkova (Aphananthe aspera) all belong to the Cannabaceae family. Japanese hackberry and Chinese zelkova, in particular, are extremely common trees in Japan. They have been used for timber, and young trees are frequently seen along roadsides in urban areas. To distinguish them, check the shape of their leaves...

ecological-information.com

Enokigusa is divided into two types: velvet enokigusa and long-leaved enokigusa.

Although not widely known, two varieties of hackberry have been identified (Kanagawa Prefecture Flora Survey Association, 2018).

Velvet hawkweed f. velutina has stems densely covered with upward-curving hairs, and ovate leaves with blunt tips, densely covered with long, obliquely ascending hairs on the veins and fine, erect hairs between the veins, giving them a velvety feel to the touch. It can be found in cultivated fields and roadside grasslands.

*Lysimachia japonica f. glareosa* has small leaves that are uniform in shape and size from the lower to the upper part of the stem. The underside of the leaves has long, erect or obliquely ascending hairs on the veins, sometimes also growing between the veins. While the amount of hair varies, there are no fine, erect hairs between the veins, so it does not feel particularly velvety to the touch. It can be found on roadsides in urban areas and in dry, bare ground.

Basically, velvet hackberry has leaves that are not very pointed at the tip and have many hairs, while long-leaved hackberry has leaves that are pointed at the tip and have fewer hairs, which is how they can be distinguished.

However, the "Flora of Kanagawa Prefecture 2018," which surveyed plants in Kanagawa Prefecture, states that "when many specimens are collected, there are many that are difficult to classify, and this time we were unable to create separate distribution maps." There are also many intermediate individuals, and it seems possible that they may no longer be distinguished in the future.

A mechanism where one male flower is received by another female flower.

The flowering period of the Japanese hackberry (Enokigusa) is from August to October. The inflorescence grows in the leaf axils, and the reddish, spike-like structures are the male inflorescences, which are covered with countless tiny male flowers. Of course, the male flowers contain a large amount of pollen. Just below them, the inconspicuous female flowers are arranged, enclosed in small, leaf-like structures called bracts. This structure is unprecedented. Why is it arranged this way?

This is thought to be because the red male flowers "drop" onto the bracts and combine with the female flowers for self-pollination (Osada, 1985). In fact, this has been observed. It seems to be a very well-structured and clever mechanism.

However, it seems to have a fatal flaw: this pollination method is limited to self-pollination. Does it not require genes from other individuals?

Generally, a lack of genetic diversity is thought to make organisms more vulnerable to changes in the natural environment and more susceptible to the effects of parasitic organisms such as viruses and bacteria.

Why go through such a roundabout pollination process? They usually rely on wind pollination too!?

If a plant truly wants to self-pollinate, it should simply place male and female flowers next to each other or produce cleistogamous flowers that don't open their petals. Some plants actually do this, so why go through such a roundabout process?

Considering all of this, we can only suspect that another method of pollination is at work. However, both the male and female flowers of the hackberry plant are small, pale in color, and the pollen is also small, so it seems unlikely that insects would be able to reach them. So how is the pollen being transported?

According to research papers on species of the genus *Utricularia* that are particularly close to *Utricularia japonica* found overseas, it has been confirmed that these species are wind-pollinated, meaning their pollen is carried by the wind (Sagun et al., 2010; Hernández-Villa et al., 2020).

Some research has also been conducted on Japanese hackberry (Tanaka, 2000). This research also points out that hackberry is wind-pollinated. According to this research, the stamens of the male flowers of hackberry have a function that allows them to repel and scatter pollen.

Generally, plants with stamens that spring back bloom in sheltered environments with little wind, such as gaps in forests or cultivated fields, where they are clustered together with other tall plants. In such environments, pollen has fewer opportunities to be blown away or dispersed far, so it releases pollen spontaneously. This is thought to be a good example of the Japanese hackberry (Celtis sinensis).

It seems natural to assume that the reason they go through the troublesome process of self-pollination is to ensure opportunities for cross-pollination by wind.

In short, hackberry plants are pollinated in two ways: self-pollination, where they drop their pollen, and cross-pollination, where they are carried out by the wind. However, there are currently no studies focusing on the proportion of pollination that occurs through these two methods, so it remains unknown. It can be said that this plant is still shrouded in mystery due to a lack of research. It may be unassuming because it does not rely on insects for pollination, but it can still be said to be a beautiful flower in its own right.

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

The fruit is a capsule that is spherical, about 3 mm in diameter, and contains three seeds, each about 1.5 mm in diameter. These seeds have a tissue called an elaiosome that serves as food for ants (Nakanishi, 1999; Fujii et al., 2012). Ants visit the plant, targeting the elaiosome, and disperse the seeds by carrying them away.

A study conducted in Hyogo Prefecture showed that when brown ants were presented with seeds of the Japanese elm (Lamium amplexicaule), they were recorded to have carried them away (Fujii et al., 2012). Therefore, it is possible that seeds are dispersed by brown ants in the wild. Since brown ants are extremely common in fields and urban areas, it is very understandable that Japanese elm can be found in similar locations.

References

Fujii, M., Kosaka, A., & Masui, K. 2012. Plants that rely on ants to disperse their seeds. Kyosei no Hiroba 7: 63-68. ISSN: 1881-2147, https://www.hitohaku.jp/publication/book/kyousei7_063.pdf

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

Hernández-Villa, V., Vibrans, H., Uscanga-Mortera, E., & Aguirre-Jaimes, A. 2020. Floral visitors and pollinator dependence are related to floral display size and plant height in native weeds of central Mexico. Flora 262: 151505. ISSN: 0367-2530, https://doi.org/10.1016/j.flora.2019.151505

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

Nagata, Takemasa. 1985. Introduction to Identifying Wildflowers: A Field Guide (Vol. 7: Primroses). Hoikusha, Osaka. 206pp. ISBN: 9784586310074

Nakanishi, Hiroki. 1999. Seed dispersal by ants. In: Ueda, Keisuke (Ed.), Seed Dispersal: The Evolution of Mutual Aid Vol. 2: Forests Created by Animals (pp. 104-117). Tsukiji Shokan. ISBN: 9784806711933

Sagun, VG, Levin, GA, & Van Welzen, PC 2010. Revision and phylogeny of Acalypha (Euphorbiaceae) in Malesia. Blumea 55(1): 21-60. ISSN: 0006-5196, https://doi.org/10.3767/000651910X499141

Satake, Yoshisuke. 1999. Wild Plants of Japan (New Edition, Woody Plants 1). Heibonsha, Tokyo. 321pp. ISBN: 9784582535044

Tanaka, Hajime. 2000. Pollen size and dispersal mode of wind-pollinated angiosperms. Journal of Plant Research 75(2): 116-122. ISSN: 0022-2062, https://doi.org/10.51033/jjapbot.75_2_9406

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

Japanese wax tree (Rhus sylvestris), Japanese lacquer tree (Rhus verniciflua), and Japanese lacquer tree (Rhus trichocarpa) all belong to the Rhus genus and are relatively common even in urban areas. They are similar species often seen in gardens and along roadsides, characterized by their odd-pinnately compound leaves. Distinguishing between them is difficult, and careful observation of the leaves is essential. The number of leaflets and the amount of hair are important clues, so be sure to record them. Japanese wax trees (Rhus sylvestris) are used for Japanese candles, and Japanese lacquer trees (Rhus trichocarpa) are used for lacquerware, demonstrating their long history of use in Japan. The rash caused by Japanese lacquer is a type of allergic contact dermatitis caused by urushiol, which is a malfunction of the human body . However, it is possible that the Japanese lacquer trees intentionally target this reaction. The flowers are inconspicuous and not very noticeable, but they are quite popular with insects, perhaps due to their high pollen content. The fat-rich fruits seem to be a persistent favorite of some birds, such as crows. Furthermore, there is an evolutionary secret to the autumn foliage, with the theory that the contrast makes the fruits stand out. This article will explain the classification, history, pollination ecology, and seed dispersal of Japanese lacquer trees (Rhus trichocarpa).

What are Japanese wax tree, Japanese lacquer tree, and Japanese lacquer tree?

Toxicodendron succedaneum, also known as the Japanese wax tree (Toxicodendron succedaneum), is a deciduous tree distributed in Honshu (west of the Kanto region), Shikoku, Kyushu, and the Ryukyu Islands in Japan; as well as in China, Taiwan, Malaysia, and India. It is commonly found growing wild in warm mountainous areas, especially along coastal regions.

Toxicodendron sylvestre, also known as Japanese wax tree (Toxicodendron sylvestre), is a deciduous small tree that grows in lowlands and mountainous areas and is distributed in Honshu (west of the Kanto region), Shikoku, Kyushu, and the Ryukyu Islands in Japan; as well as in China and Taiwan.

Toxicodendron vernicifluum, also known as lacquer tree, is native to China and India. In Japan, it is cultivated for lacquer harvesting and has escaped cultivation in hilly areas.

Toxicodendron trichocarpum, also known as mountain lacquer tree, is a deciduous shrub distributed in Hokkaido, Honshu, Shikoku, and Kyushu in Japan; the Kuril Islands; Korea; and China. It is commonly found in mountainous areas and rarely in lowland hills.

Both belong to the Anacardiaceae family, genus Rhus, and are known as pioneer species that commonly grow in gardens and along roadsides, characterized by their odd-pinnately compound leaves. However, they are very similar and are often confused. Another commonality is that they are dioecious, meaning they have separate male and female plants.

What are the differences between Japanese wax tree (Rhus sylvestris), Japanese lacquer tree (Rhus trichocarpa), Japanese lacquer tree (Rhus verniciflua), and Japanese lacquer tree (Rhus trichocarpa)?

However, by carefully observing the leaves, they can be clearly distinguished as follows (Hayashi, 2014; Kanagawa Prefecture Flora Survey Association, 2018).

First, the leaflets of the Japanese lacquer tree (Urushi) are large, about 15 cm long, and usually number only 4 to 5 pairs. On the other hand, the leaflets of the other three species are somewhat smaller, about 10 cm long, and usually number 4 to 8 pairs. It's also worth noting that the Japanese lacquer tree is originally a cultivated species, so it's less commonly seen compared to the other three wild species.

Regarding the remaining three species, in the case of Rhus succedanea, the plant body and leaves are hairless (although some individuals rarely have hairs on their winter buds), the underside of the leaves appears white due to lipids, and the lateral veins are less prominent compared to Rhus sylvestris. On the other hand, in Rhus sylvestris and Rhus trichocarpa, the plant body and leaves are hairy, and the underside of the leaves is not white.

The differences between Rhus sylvestris and Rhus lacquerus are that in Rhus sylvestris, the lateral veins of the leaflets are numerous and prominent, generally with long and short veins alternating, and the fruit lacks bristles, while in Rhus lacquerus, the lateral veins of the leaflets are few in number, the lowest pair of veins in the compound leaflets are generally slightly smaller than the others, and the fruit has bristles.

You might get confused between Japanese rhododendron and lacquer tree because both have hairless fruits, but Japanese rhododendron has hairs on both sides of its leaflets, while lacquer tree has hairless fruit only on the upper surface of its leaflets.

Identifying the species based on the redness of the leaf stalk is probably not possible, as while Japanese lacquer tree and poison ivy tend to have reddish stalks, there are exceptions.

Although sumac is also in the Anacardiaceae family, it belongs to a different genus and can be easily distinguished by the wings that appear between the leaflets on the leaf axis.

Are there any other similar species?

Ailanthus altissima, also known as "Urushi," is a species whose Japanese name includes the word "urushi" (lacquer tree), and it shares similarities with other species, such as having odd-pinnately compound leaves.

However, Ailanthus altissima belongs to the Simaroubaceae family and is classified differently, resulting in several differences. Please see the separate article for more details.

What are the differences between *Pyrus pyrifolia*, *Ailanthus altissima*, and *Lucifer praecox*? An explanation of how to distinguish between similar species.

Both *Pachypodium sibiricum* and *Ailanthus altissima* belong to the Simaroubaceae family and are deciduous trees sometimes planted in Japan. *Ailanthus altissima*, in particular, is known for its rapid growth and widespread naturalization worldwide. However, they share similarities, such as having odd-pinnately compound leaves, so those unfamiliar with them might not distinguish them...

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There is a species called Chinese tallow tree (Triadica sebifera) that has a similar name to the Japanese wax tree (Rhus succedanea). While it is similar in that its seeds contain fat and turn into wax, it belongs to the Euphorbiaceae family and the shape of its leaves, flowers, and fruits are all different. Please see the separate article for more details.

What are the differences between Chinese tallow tree and Japanese wax tree? We explain how to distinguish between similar species! Why did the white seeds, which contain a lot of fat, evolve?

Both the Chinese tallow tree (Toxicodendron sylvaticum) and the Japanese wax tree (Toxicodendron succedaneum) are deciduous trees, and both share the name "haze." This name comes from the fact that their fruits or seeds contain a large amount of fat, which has historically been used as wax. However, perhaps because of this, the Chinese tallow tree and the Japanese wax tree are often confused...

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How are the lacquer trees used? Japanese wax trees (Rhus succedanea) are used for making Japanese candles, while lacquer trees (Rhus urushi) are used for lacquering.

The fruit of the Japanese wax tree (Rhus succedanea) contains a lot of fat. For this reason, it was used to make Japanese candles, and was specifically called "haze wax."

Western candles are made by using a cotton wick and pouring beeswax, animal fat, or paraffin into a mold and letting it harden, while Japanese candles are made by using a wick taken from a rush plant and washi paper as a core, and then applying layers of wood wax taken from the Japanese wax tree.

The origins of Japanese candles are said to date back to the Nanboku-cho period, as they appear in the Taiheiki (a historical chronicle) around 1375. Production peaked during the Edo period and the late Edo period. At that time, Japanese candles were mainly consumed by a small number of merchants and samurai, and were not available to ordinary people.

Urushi lacquer is harvested by damaging the bark to obtain raw lacquer. The drying and hardening of lacquer occurs through the oxidative polymerization of urushiol by the action of laccase and oxygen. Once hardened, lacquer is resistant to heat, moisture, acid, alkali, alcohol, and oil, and also has anti-corrosion and insect-repellent properties, so it was used for lacquering and for tableware and furniture. Currently, due to the widespread use of plastics and other materials, production areas are limited.

It is believed that lacquer painting was already being practiced during the Jomon period. The wild lacquer trees found in the mountains of Japan today are remnants of those planted by humans (Nōshiro, 2007).

Why does poison ivy cause a rash?

All plants in the Anacardiaceae family contain urushiol, and inflammation occurs when an allergic reaction occurs to this substance. The degree of inflammation varies from person to person; symptoms may appear only on the area where the lacquer sap came into contact, or the inflammation may occur throughout the body (Nōshiro, 2007). In most cases, blisters and itching occur, which are most severe in the first week and usually disappear within two to three weeks.

The strength of these plants varies depending on the species of the Anacardiaceae family; among the Japanese species, lacquer trees (Rhus javanica) are considered the strongest, while sumac trees (Rhus javanica) are the weakest.

This allergic reaction (not limited to urushiol) normally occurs in response to large parasites, but it occurs when the human body mistakenly identifies urushiol (Palm et al, 2012).

But if that's the case, is this kind of "rash" intentionally caused by the plant?

This is a very difficult question, but it is a possibility. In fact, it is known that Japanese lacquer tree (Rhus trichocarpa) is an unpalatable plant for Japanese deer (Ishida et al., 2012).

If that's the case, then it could be said that poison ivy and its relatives even utilize the malfunction of the mammalian immune system.

On the other hand, it also possesses strong antifungal properties (Kim et al., 1997), so it's possible that it evolved for this purpose as well.

What is the structure of a flower?

The Japanese wax tree (Rhus succedanea) flowers from May to June (Mogi et al., 2000). It bears numerous small, yellowish-green flowers in a conical shape. The inflorescence is 5-10 cm long. The petals are 5 in number, about 2 mm long, and curve backward.

Japanese wax tree (Rhus japonica) flowers from May to June. It bears numerous small, yellowish-green male or female flowers in a conical shape. The inflorescence is 8-15 cm long and has curved, spreading hairs. There are more flowers in the male inflorescence than in the female inflorescence. The petals are 5 in number, oval-shaped, and about 2 mm long. The petals of the male flowers are recurved, and the stamens protrude from the outside of the flower.

Japanese lacquer tree (Rhus trichocarpa) flowers from May to June. It bears numerous small, yellowish-green flowers in a conical shape. The inflorescence is 15-30 cm long, and the axis of the inflorescence is densely covered with coarse hairs. The petals are five in number, narrowly oblong, and about 2 mm long. The petals of the male flowers are recurved, and the stamens protrude outside the flower. The ovary of the female flower is densely covered with bristles. The style protrudes outside the flower, and the stigma is three-lobed.

The lacquer tree (Urushi) is also very similar to the three species mentioned above, and overall there isn't much difference. The fact that the petals of the male flowers are curved back might be to make the pollen more visible.

While pollinating insects are under-researched, many of them seem to be primarily attracted to pollen!

Although I couldn't find any literature on insects that visit Japanese wax trees, internet searches confirmed records of the seventeen-spotted flower beetle, the green flower beetle, the red longhorn beetle, the common blue butterfly, and the small bumblebee visiting the tree.

When we also investigated the insects that visit the flowers of the Japanese wax tree, we could not find any comprehensive studies, and the only records we found were of bees such as the Japanese honeybee (Fujiwara et al., 2014), the genus *Hymenoptera* (Miyamoto, 1960), and the *Hymenoptera japonica* (Ichikawa and Ohara, 2009).

Interestingly, however, there are records of a fly called *Hisamatsu wasp-like hoverfly*, which mimics the potter wasp so closely that even humans could mistake it for the real thing (Ichikawa and Ohara, 2009). It is unclear whether this is a common occurrence, but the existence of a fly that mimics a wasp to feed on nectar suggests that there may be a complex ecosystem surrounding this flower.

Detailed research has been conducted on poison ivy, and it has been found that two types of insects visit its flowers: the majority are nonsocial wasps, flies, and beetles, and a small number are social bees (Matsuyama et al., 2008; Matsuyama at al., 2009).

In summary, it seems that the entire genus *Rhus* attracts a large number of bees, flies, and beetles seeking pollen.

By the way, since the genus Rhus is dioecious (having separate male and female plants), isn't there a risk that the insects that visit the plants will be biased towards the male flowers, which contain pollen that is a rich source of protein, and thus pollination will not be successful?

Research on poison ivy has shown that some social bees do indeed visit only male flowers, resulting in insufficient pollination (Matsuyama et al., 2009). However, the vast majority of other non-social bees, flies, and beetles visit without regard for this, and thus seem to achieve at least minimal pollination.

The mechanism behind this is explained as follows: social bees are sensitive to the amount of reward and tend to favor male flowers, while non-social bees, beetles, and flies do not strongly distinguish between different amounts of reward and will visit flowers even if only for nectar, thus visiting both male and female flowers without bias.

Although not mentioned in this study, it is also possible that female flowers deceive insects by making them mistakenly believe they are male flowers, in other words, by "mimicry." Such instances are commonly observed in other plants and are known as "intersexual mimicry."

Why are fruits so oily? That bird that loves fat is a big fan!?

While there are differences in the presence or absence of bristles, the fruits of the Rhus genus are generally drupe-like, flattened fruits with a large amount of fat in the flesh. As mentioned above, this is why they were used as a raw material for Japanese candles, but who uses them in nature?

Research has shown that these fruits are eaten by birds, which then disperse the seeds.

However, when it comes to fruit, humans tend to prefer sweeter fruits, but why do they have these particular shapes and components?

While this isn't fully understood, it's possible that by altering the composition, nutrients like nitrogen and lipids (which serve as energy sources) are added, differentiating the fruit from those of other plants. This might also influence the types of birds that prefer it.

In fact, a bird that particularly prefers the genus Rhus has been identified (Ueda, 1999). That bird is the crow. In a study in Osaka Prefecture, by examining pellets and droppings regurgitated by crows, it was found that approximately 64% of the seeds were from the genus Rhus. Crows seem to prefer fatty fruits to sweet ones.

Another study in Japan that directly observed animals eating the fruit of the Japanese rhododendron using binoculars found that five species—the pale thrush, thrush, brown-eared bulbul, Daurian redstart, and shrike—consumed the fruit. The pale thrush and thrush, in particular, spend long periods of time on the rhododendron and are thought to contribute to seed dispersal (Sato and Sakai, 2001). The bird considered to contribute the most to seed dispersal is the thrush, which, unlike the pale thrush, does not have a winter territory and therefore defecates over a wide area.

The reason why young trees of the genus Rhus can sometimes be found even in small green spaces is thought to be due to seed dispersal by birds that like fat.

Did the genus *Rhus* change color in the red "to make its fruit more conspicuous"?!

An interesting hypothesis has been proposed regarding the fruits of the genus Rhus (Kamitani, 1999; Lev-Yadun, 2022).

One theory suggests that the red leaves of the Rhus genus turn red in early autumn because the contrast makes the fruits more conspicuous, attracting birds to eat them. This is known as the foliar fruit flags hypothesis.

Some argue that female plants that have actually produced fruit change color earlier than immature trees or male plants.

However, there are counterarguments to this hypothesis, such as the lack of any factual basis for it, and the significant disadvantages of the leaves changing color prematurely. Furthermore, plants with wind-dispersed fruits also frequently change color, which would likely confuse birds.

However, experiments have shown that the artificial red color created around the fruit has an effect of attracting birds, so it is now thought that this effect may exist, albeit very limited.

Even the colorful autumn leaves that adorn the seasons may actually play a more important role for some plants than simply shedding their leaves!

References

Fujiwara, A., Nishihiro, J., & Washitani, I. 2014. Ecosystem service evaluation of Japanese honeybees in a Satoyama nature restoration project area: Flower resource utilization and colony development. Conservation Ecology Research 19(1): 39-51. ISSN: 1342-4327, https://doi.org/10.18960/hozen.19.1_39

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

Ichikawa, Toshihide and Ohara, Kenji. 2009. Adult behavior of *Hyperva* and *Hyperva* (Diptera, Syrphidae). Bulletin of the Faculty of Agriculture, Kagawa University 61(114): 1-10. ISSN: 0368-5128, http://id.nii.ac.jp/1731/00003525/

Ishida, H., Kuroda, Y., Hashimoto, Y., Sawada, Y., Ema, K., and Hattori, Y. 2010. The impact of Japanese deer on species diversity and species composition in warm temperate deciduous secondary forests. Conservation Ecology Research 15(2): 219-229. https://doi.org/10.18960/hozen.15.2_219

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

Kim, MJ, Kim, CJ, & Kwak, SS 1997. Antifungal activity of urushiol components in the sap of Korean lacquer tree (Rhus vernicifera Stokes). Korean Journal of Plant Resources 10(3): 231-234. https://koreascience.kr/article/JAKO199711920278770.page

Lev-Yadun, S. 2022. The phenomenon of red and yellow autumn leaves: Hypotheses, agreements and disagreements. Journal of Evolutionary Biology 35(10): 1245-1282. https://doi.org/10.1111/jeb.14069

Matsuyama, Shuhei; Osawa, Naoya; and Sakimoto, Michinori. 2008. Reproductive ecology of *Rhus trichocarpa*: The role of dioecious inflorescences and generalist pollinators in reproductive success. Abstracts of the Annual Meeting of the Ecological Society of Japan 55: P3-078. https://www.esj.ne.jp/meeting/abst/55/P3-078.html

Matsuyama, S., Osawa, N., & Sakimoto, M. 2009. Generalist pollinators in the dioecious shrub Rhus trichocarpa Miq.(Anacardiaceae) and their role in reproductive success. Plant Species Biology 24(3): 215-224. https://doi.org/10.1111/j.1442-1984.2009.00258.x

Miyamoto, S. 1960. Flower-visiting behavior of 14 species of flower wasps of the family Carangidae: Ecological studies of flower wasps of Japan XIV. Konchu (Japanese Journal of Insects) 28(2): 65-86. ISSN: 0915-5805, https://dl.ndl.go.jp/pid/10649907

Mogi, Toru; Ota, Kazuo; Katsuyama, Teruo; Takahashi, Hideo; Shirokawa, Shiro; Yoshiyama, Hiroshi; Ishii, Hidemi; Sakio, Hitoshi; and Nakagawa, Shigetoshi. 2000. Flowers Blooming on Trees: Polypetalous Flowers (Vol. 2, 2nd edition). Yama-kei Publishers, Tokyo. 719pp. ISBN: 9784635070041

Noshiro, Shuichi. 2007. Urushi (Japanese lacquer tree). Forest Science 50: 39-41. https://doi.org/10.11519/jjsk.50.0_39

Palm, NW, Rosenstein, RK, & Medzhitov, R. 2012. Allergic host defences. Nature 484(7395): 465-472. https://doi.org/10.1038/nature11047

Sato, Shigeho & Sakai, Atsushi. 2001. Predation process of the fruit of Rhus sylvestris by birds. Forest Applied Research 10(1): 63-67. ISSN: 1342-9493, https://doi.org/10.20660/applfor.10.1_63

Kamitani, Tomohiko. 1999. The two-color display strategy of fruits. In: Ueda, Keisuke (Ed.), Seed Dispersal: The Evolution of Mutual Aid Vol. 1 Seeds Carried by Birds (pp. 52-64). Tsukiji Shokan. ISBN: 9784806711926

Ueda, Keisuke. 1999. Unexpected Birds' Unexpected Preferences: Who Eats the Inconspicuous "Dry Fruit"?. In: Ueda, Keisuke (Ed.), Seed Dispersal: The Evolution of Mutual Aid Vol. 1: Seeds Carried by Birds (pp. 64-75). Tsukiji Shokan. ISBN: 9784806711926

Source

This article has been significantly expanded from the content included in the following book.