Duckweed (English spelling)

Japanese: アオウキクサ（英語表記）duckweed

A small aquatic plant of the duckweed family that floats on the surface of ponds and rice paddies (illustration). The thallus that floats on the water surface is 2 to 3 mm long and somewhat narrow and oval, with two roots that are lowered into the water. This thallus is thought to be a shortened stem and leaf combined, and has three veins. One or two young thallus grow laterally from near the base, and by repeated germination and division, usually form a group of several thallus. Flowers form on the underside of the thallus, and two male flowers consisting of only one stamen and a female flower consisting of one pistil are enclosed in a common small bract.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

池や水田の水面に浮遊する小型のウキクサ科水草（イラスト）。小さな水草で，水面に浮かぶ葉状体は長さ2～3mmのやや狭い卵形で，2本の根を水中におろす。この葉状体は短縮した茎と葉が合体したものと考えられ，3本の葉脈がある。基部近くから若い葉状体を1～2個側生し，発芽分裂をくり返し，普通は数個の葉状体から成る群を形成する。花は葉状体の下面に形成され，1本のおしべだけから成る雄花2個と1個のめしべから成る雌花が，共通した小さな苞につつまれている。

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