Yabumao - Yabumao

A perennial plant of the Urticaceae family (APG classification: Urticaceae). It is a relative of the Asclepias japonica (Curticaceae) that grows in the bushes of low mountain areas, hence the name. The stems grow in clusters of several, reaching a height of 1.5 meters, are fibrous and hard, and sometimes split into short branches in the middle. The leaves are stalked, opposite, oval, and 7-20 cm long excluding the stalk. The edges are double-serrated, but the size and density of the serrations vary greatly. Both sides of the leaves are covered with coarse soft hairs. The inflorescences are sexed in the leaf axils, with male inflorescences growing from the middle of the stem and being cone-shaped, and female inflorescences growing from the upper part and being spike-shaped, but male inflorescences often do not grow. There are known triploid to pentaploid forms that produce azygosity seeds without fertilization, but no form that reproduces sexually is known. It is distributed in the low mountain areas from Hokkaido to Kyushu, and outside Japan, it is widely distributed in the warm temperate zone of East Asia. Its Chinese name is Nosenma. This species actively hybridizes with other sexually reproducing species, making it extremely difficult to distinguish it from closely related species. In northern Kyushu, many species with coarsely serrated leaves and thin inflorescences are found, and they are called Togariba Yabumao (B. japonica (Lf) Miq. var. japonica , but the scientific name was given to this species earlier. The genus Yabumao contains nearly 100 species worldwide, but classification is difficult because there are many species with large variations that form azygosity seeds, especially in the temperate zone of East Asia.

[Hiroshi Yonekura December 13, 2019]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

イラクサ科（APG分類：イラクサ科）の多年草。低山地の藪(やぶ)に生える真苧(まお)（ナンバンカラムシのこと）の仲間なのでこの名がある。茎は数本固まって出て高さ1.5メートルに達し、繊維質で硬く、ときに中部で短い枝を分けることがある。葉は柄(え)があって対生し、卵円形で長さは柄を除き7～20センチメートル。縁(へり)には重鋸歯(じゅうきょし)があるが、鋸歯の大きさや密度には大きな変異がある。葉の両面には粗い軟毛がある。花序は葉腋(ようえき)について雌雄別となり、雄花序は茎の中部から出て円錐(えんすい)状、雌花序は上部から出て穂状となるが、雄花序が出ないことも多い。受精しないで種子をつくる無融合種子形成を行う三～五倍体が知られるが、有性生殖を行う型は知られていない。北海道から九州の低山地に分布し、国外では東アジアの暖温帯に広く分布する。中国名は野線麻という。本種は有性生殖を行う他の種と盛んに交雑するため、近縁種との区別はきわめてむずかしい。九州北部には葉の鋸歯が粗く花序が細いものが多くみられ、トガリバヤブマオB. japonica (L.f.) Miq. var. japonicaというが、学名はこちらの方に早くつけられた。ヤブマオ属は世界に100種近くを含むが、とくに東アジアの温帯域では無融合種子形成を行う変異の大きい種が多く存在するために分類はむずかしい。

［米倉浩司　2019年12月13日］

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