Euphorbia - Euphorbia

A biennial plant of the Euphorbiaceae family (APG classification: Euphorbiaceae). The stem usually branches from the base and is 20-50 cm tall. There are sparse long hairs on the upper part. The leaves are alternate, the lower leaves are small, and the upper leaves are large, and are arranged in a slightly whorled shape at the end of the stem, spatula-shaped, obovate, 1-3 cm long. The tips of the leaves are round or slightly concave, the base is wedge-shaped, and the edges are serrated. The involucre leaves are obovate, yellow-green, and somewhat small. In April and May, numerous compound cup-shaped inflorescences are densely produced. The glandular bodies are elliptical and yellow. The capsules are smooth, about 3 mm in diameter, and hairless. The seeds are obovate, brown, and have raised net patterns. They grow on roadsides and riverbeds, and are widely distributed throughout Japan, as well as the warm-temperate regions of Asia and Europe. The name comes from the fact that the branched shape of the plant with yellow flowers resembles a lighthouse (candlestick). Closely related species include Takatoudai, Natsutoudai, and Nourushi. All produce cup-shaped inflorescences, with many male flowers consisting of a single stamen on the inside of the inflorescence axis, and a female flower consisting of a single pistil in the center.

[Junko Kobayashi, June 23, 2020]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

トウダイグサ科（APG分類：トウダイグサ科）の越年草。茎は普通基部から分枝し、高さ20～50センチメートル。上方にはまばらに長毛がある。葉は互生し、下部の葉は小さく、上部の葉は大きく茎の先にやや輪生状につき、へら状倒卵形で長さ1～3センチメートル。葉先は丸いかややへこみ、基部はくさび形、縁(へり)に鋸歯(きょし)がある。総包葉は倒卵形、黄緑色でやや小形。4～5月、多数の複合杯状花序を密につける。腺体(せんたい)は楕円(だえん)形で黄色。蒴果(さくか)は平滑で径約3ミリメートル、毛はない。種子は倒卵形で褐色、隆起した網紋がある。道端や川原などに生え、日本全土、およびアジア、ヨーロッパの暖帯に広く分布する。名は、黄色い花をつけて分枝した形状を、灯をつけた灯台（燭台(しょくだい)）に見立てたもの。近縁種にタカトウダイ、ナツトウダイ、ノウルシなどがある。すべて杯状花序をつくり、花序の軸の内側に1本の雄しべからなる多数の雄花と、その中央に1本の雌しべからなる雌花がある。

［小林純子　2020年6月23日］

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