This variety of the species from Japan is noted for growing in moist, swampy regions which was first identified by Dr. Fumio Maekawa around 1940.

It is a miniature size hosta only growing about 4 inches high with a spread of around 15 inches. The medium green leaves are very narrowly elliptic, shiny on top and have smooth texture. Pale lavender flowers with 4 or 5 blossoms per scape bloom in September.

According to The Hostapedia by Mark Zilis (2009), "Its strap-like foliage appears much closer to that of a Liriope than a hosta...The flowers, too, set this plant apart from other hostas. It only produces 4-5 flowers per scape, making for one of the shortest hosta blooming seasons."

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