This is a small size sport of the species H. longissima found in the Nukata district of Japan. It has joined flower lobes and some of the stamens are petaloid i.e. have tissue on them that resembles a petal. Flowers are medium purple in color with purple anthers and are borne from mid-September to October followed by viable seeds.

Mikiko Lockwood in an article on The Hosta Library titled, A Little About Japanese Hosta Terms defines the term mizu as water, 'Mizu Gibōshi' or H. longissima.