This species is native to Honshu Island in Japan. It is also known as Mizu Gibōshi and Saji Gibōshi in Japanese.

The plant forms a small size (9 inches high by 25 inches wide) mound with narrow foliage which has a shiny on top and bottom. The dark green leaves are narrowly elliptic (strap shaped), smooth textured without waves. It has average substance. Flowers are medium purple in color with purple anthers and are borne from mid-September to October followed by viable seeds.

According to The Hostapedia by Mark Zilis (2009), "...useful as a ground cover or edging plant. The late-season flowers are in bloom at a time when the shade garden is turning to fall in the northern U.S."

The New Encyclopedia of Hostas by Diana Grenfell (2009) states: "Can be grown in garden ponds successfully if the crown is kept above the water line. Is often confused with the narrowest-leaf forms of H. sieboldii... Strap-shaped leaves are among the narrowest in the genus."

Mark Zilis' Field Guide to Hostas (2014) states that this species was found in Japan in "...wetlands..."

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.

An article by Hajime Sugata of Japan in The Hosta Journal (1994 Vol. 25 No. 2) states that "H. longissima can be found abundantly near wetlands on sunny hills or along irrigation paths of rice paddies in Aichi Pref. and Gifu Pref. H. longissima grows densely and appears smaller but healthier on the sunny side of hills as opposed to the shady side. Thus, H. longissima can look like two different species.

There aren't many regionally modified forms of H. longissima, but a yellow-margined form and a white-margined form are found in Okazaki City, Nukata Town, and Shimoyama Village. A gold-leaf form has not yet been found."

"Another late-flowering species which has been around for years. It is well known and needs to be grown more. It has beautiful, dark striped (Type C) lobes and conspicuous green bracts. Its leaves are unique and a mature specimen makes a showing in the garden. Most nurseries have it for around $6.00."