Cleistoga - Heisaka

This refers to flowers whose perianth segments do not open, and which remain in buds, self-pollinating and self-fertilizing, leading to fruiting. Generally, the various parts of the flower degenerate, and there are few stamens (male stamens) and pistils (female females), and the number of pollen grains and ovules produced within them is also small. Usually, the anthers of the stamens and the stigma of the pistil are close to each other, the anthers do not dehisce, and the pollen germinates within the anthers. The pollen tube breaks through the anther wall, extends, and enters the pistil from the stigma, where fertilization occurs.

Cleistogamous flowers are specialized flowers for self-pollination, but there are various stages between them and normal flowers. They are widely seen in angiosperms such as the genera Acanthus, Oxalis, and Viola, and many of them produce normal flowers in spring and form cleistogamous flowers in summer. In the water plant Baikamo (an aquatic plant that grows in ponds and streams), the flowers rise to the water surface and open, but when the water level rises, the flowers remain underwater and do not open, but become cleistogamous flowers and are pollinated and fertilized.

[Michio Tamura]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

花被(かひ)片が開かず、つぼみのまま自家受粉・自家受精し、結実に至る花をいう。一般に花の各部分は退化し、雄蕊(ゆうずい)（雄しべ）や雌蕊（雌しべ）の数も少なく、また、それらの中につくられる花粉や胚珠(はいしゅ)の数も少ない。普通、雄蕊の葯(やく)と雌蕊の柱頭は接近し、葯は裂開せず、花粉は葯の中で発芽する。花粉管は葯壁を破って伸長し、柱頭から雌蕊の中に入って受精する。

　閉鎖花は自家受粉のために特殊化した花であるが、正常花との間にはさまざまな段階が認められる。シロカネソウ属、カタバミ属、スミレ属などの被子植物に広くみられるが、なかには、春には正常花をつけ、夏になると閉鎖花を形成するものも多い。バイカモ（池や小川に生える水草）では、花は水面に出て開くが、水かさが増すと花は水中にあって開花せず、閉鎖花となって受粉・受精する。

［田村道夫］

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