"Mizu-kimbai" (Ludwigia stipulacea) belongs to Onagraceae (the Evening primrose family). It is a perennial herb that is distributed to Honshu, Shikoku and Kyushu in Japan, as well as Taiwan. This herb grows in ponds, rivers and rice fields, and rearly forms a clump. It spreads by long rhizomes and takes white espiratory roots at the nodes. The yellow flowers bloom from July to September. The flowers last one day. The Japanese is derive from the similar flower of "Kinbai-so" (Trollius hondoensis).