せきしょうも (石菖藻) [Index] [Back] わが国の各地をはじめ、アジアやオーストラリアに分布しています。平野部の池沼や小河川など流れのあるところに群生します。沈水性で茎は短く、葉を束生して、走出枝を出して栄養的に繁殖します。葉は線形で長さ１５〜７０センチ、幅３〜７ミリ、先端部の辺縁には小さい鋸歯があります。雌雄異株です。８月から１０月ごろ、根の基部かららせん状の花柄が水面まで伸び、長さ１センチほどの黄白色の小さな雌花を咲かせます。雄花は基部から切れて水面上を漂い、雄性花水面媒します。受粉後、雌花の花茎は螺旋状にねじれて縮み、雌花は水中に引き込まれて結実します。 トチカガミ科セキショウモ属の常緑多年草で、学名は Vallisneria natans (syn. Vallisneria natans var. natans、Vallisneria asiatica)。英名は Asian tape grass、Straight eelgrass。 The Asian tape grass (Vallisneria natans) belongs to Hydrocharitaceae (the Frogbit family). It is a perennial herb that is distributed throughout Japan, as well as in Asia and Australia. It grows in colonies in flowing waters such as ponds, marshes, and small rivers in lowland areas. It is a submerged plant with short stems; the leaves grow in clusters, and it reproduces vegetatively by producing stolons. The leaves are linear, 15-70 cm long and 3-7 mm wide, with small serrations along the edges of the tips. It is dioecious. From August to October, spiral-shaped flower stalks extend from the base of the roots to the water’s surface, bearing small, yellowish-white female flowers about 1 cm long. The male flowers break off at the base and float on the water's surface, and pollination occurs via water surface (male flower hydrophily). After pollination, the flower stalk of the female flower twists into a spiral and shrinks, and the female flower is drawn underwater to set fruit. 茨城県つくば市「つくば実験植物園」にて、2026年03月07日撮影。 Shu Suehiro shu@botanic.jp