ヒツジグサの花は実際10時くらいから咲き始めます。昼下がりの未の刻に開ききり、16時くらいに咲き終わり。３日間、開閉を繰り返します。
The pygmy water lily begins to open around 10:00 AM, reaches full bloom in the early afternoon—traditionally known in Japan as Hitsuji-no-koku (1:00 PM to 3:00 PM)—and closes by around 4:00 PM. It repeats this cycle of opening and closing over three consecutive days.
【仮名】ヒツジグサ
【和名】未草
【英名】Pygmy Water Lily
【学名】Nymphaea tetragona
【誕生】07/ 24
【開花】06, 07, 08, 09, 10月
【花色】White
ヒツジグサ
ヒツジグサの概要
ヒツジグサはスイレン科の多年生浮葉植物です。日本では北海道から本州、四国、九州まで、国外では東アジアから欧州北部、北米北部まで広く分布。浅い池沼、湿原など、穏やかな水辺で自生しています。花は雌性先熟で３日間、開閉を繰り返し。未の刻に咲き、申の刻に閉じます。
ヒツジグサの名前
ヒツジグサの和名の「未」は時刻の旧称で13～15時の間。花が昼下がりに開ききり、夕方に閉じます。英名ピグミー・ウォーター・リリーは「小さな睡蓮」という意味。属名ニンフェアは水の精霊「ニンフ」に由来し、種小名テトラゴナは「四角形の」という意味で花托に由来します。
ヒツジグサの姿形
ヒツジグサは根茎の節々から髭根を伸ばし、底土をつかみます。葉は深く切れ込んだ卵形。根茎から葉柄を伸ばし、水面に浮かびます。花は根茎から花柄を伸ばし、萼片が４枚、花弁が10～12枚、雄しべが20～40本。水中で壺状の蒴果を結び、熟すと種子が仮種皮で浮き、運ばれます。
ヒツジグサの受粉
ヒツジグサは実際、10時くらいから咲き始め、16時くらいに咲き終わり。１日目は雌しべが盤状の柱頭に甘い粘液を満たし、他の花の花粉をつけた昆虫を引き寄せます。２日目は扁平な雄しべが葯から花粉を出し、昆虫が他の花へと運搬。３日目は送受粉を終えた花が水中に沈みます。
Pygmy Water Lily
The pygmy water lily is a perennial, floating-leaved aquatic plant belonging to the Nymphaeaceae family. It is widely distributed across Japan—from Hokkaido to Honshu, Shikoku, and Kyushu—as well as internationally, ranging from East Asia to northern Europe and northern North America. It thrives in calm waters such as shallow ponds, marshes, and wetlands. The flowers are protogynous (the female organs mature before the male ones) and undergo a three-day cycle of opening and closing; they bloom during Hitsuji-no-koku (early afternoon) and close during Saru-no-koku (late afternoon).
The Japanese name for the pygmy water lily, Hitsuji-gusa, translates to “plant of the Sheep Hour.” Hitsuji (Sheep) refers to a traditional Japanese timekeeping term for the hours between 1:00 PM and 3:00 PM. This name reflects how the flower reaches full bloom in the early afternoon and closes toward evening. The genus name Nymphaea derives from the water nymphs of Greek mythology, while the specific epithet tetragona means “four-angled,” referring to the distinct shape of its receptacle.
The pygmy water lily extends fibrous roots from the nodes of its rhizome, anchoring itself securely in the underwater sediment. Its floating, deeply notched, oval leaves grow on long petioles (leaf stalks) attached to the rhizome. The flowers also rise from the rhizome on long flower stalks (pedicels), each featuring four sepals, 10 to 12 petals, and 20 to 40 stamens. Underwater, it forms an urn-shaped capsule fruit; once ripe, the seeds—encased in buoyant arils—float to the surface and disperse.
In reality, the pygmy water lily begins opening around 10:00 AM and closes for the day by about 4:00 PM. On the first day, the stigma produces a sweet, viscous fluid to attract insects carrying pollen from other flowers. On the second day, the flattened stamens release pollen from their anthers, which insects then carry to nearby blooms. On the third day, once pollination is complete, the flower sinks beneath the water’s surface.
