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わが国の本州、琵琶湖水系だけに分布する固有種です。沈水植物で、ランナーを伸ばして群生します。葉は紐状で、１メートルくらいの長さになり、螺旋状にねじれるのが特徴です。雌雄異株です。８月から１１月ごろ、長い花茎を伸ばして水面上に小さな雌花を咲かせ、分離されて漂う雄花と受粉します。
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トチカガミ科セキショウモ属の多年草で、学名は Vallisneria natans var. biwaensis。英名はありません。
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"Nejire-mo" (Vallisneria natans var. biwaensis) belongs to Hydrocharitaceae (the Frogbit family). It is a perennial herb that is endemic to Japan and distributed only in river system of Lake Biwa. This herb is a submerged plant and grows in clusters by elongated runners. The leaves are corded about 1 m long, and defined by spiral contortion. It is dioecious. The female flowers with long flowering stalks are borne on the water surface, and pollinated with separated, wandering male flowers. The Japanese name 'Nejire-mo (Spiral alga - literally translated)' is derived from the leaf appearance.
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大阪府交野市「大阪市大付属植物園」にて、2007年05月22日撮影。
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ねじれも (捩れ藻)
shu@botanic.jp