Canadian pondweed - Canadian pondweed

A submerged perennial aquatic plant of the family Hydrocharisataceae (APG classification: Hydrocharisataceae). It resembles Hydrangea nudiflora, but is dioecious. Some species of Elodea canadensis have been introduced all over the world. Naturalized species in Japan include Elodea nuttallii (Planch.) St. John, native to North America, and Elodea densa Planch., native to South America, and only male plants of both species have been introduced. Although the stems are easily broken, they have a strong regenerative ability and reproduce asexually, distributing them in ponds and swamps throughout Japan. Elodea nuttallii usually has three whorls, 0.6 to 1.5 centimeters long, while Elodea densa usually has four to five whorls, 1 to 3 centimeters long. The male flowers of Elodea nuttallii are similar to Hydrangea nudiflora, and are solitary in the leaf axils, with three sepals and nine stamens, which detach from the sheath and release pollen on the water surface. The male flowers of Elodea canadensis resemble those of Hydrocharis majus, are white, and open in threes successively above the water surface from the theca.

[Sueo Otaki, September 19, 2018]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

トチカガミ科（APG分類：トチカガミ科）の沈水性多年生水草。クロモに似るが雌雄異株。カナダモの仲間は世界中に広く移入しているものがある。日本の帰化種には、北アメリカ原産のコカナダモE. nuttallii (Planch.) St.Johnと南アメリカ原産のオオカナダモEgeria densa Planch.があり、2種とも雄株だけが移入している。茎は折れやすいが、再生力が強く、無性繁殖して日本各地の池や沼に分布。輪生葉はコカナダモは普通は3枚、長さ0.6～1.5センチメートル、オオカナダモは普通は4～5枚、長さ1～3センチメートル。コカナダモの雄花はクロモに似ていて、葉腋(ようえき)に単生、萼片(がくへん)3枚、雄しべ9本、包鞘(ほうしょう)から脱離して水面で花粉を出す。オオカナダモの雄花はトチカガミの雄花に似ていて、白色で包鞘から順次3個水面上に開く。

［大滝末男　2018年9月19日］

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