noun
pygmy waterlily
A small species of waterlily native to East Asia, Nymphaea tetragona. The Japanese name literally means 'sheep grass', possibly from the flowering season or leaf shape.
池にヒツジグサが咲いている。
Pygmy waterlilies are blooming in the pond.
スイレン is the general term for waterlilies, while ヒツジグサ refers specifically to the pygmy waterlily (Nymphaea tetragona).
The name ヒツジグサ (未草) literally means 'sheep grass'. The exact origin is uncertain, but it may refer to the flowering time around the hour of the sheep (未の刻, roughly 2 p.m.) or to the shape of the leaves.