Japanese iris

The term "Japanese iris" encompasses three species of Irises cultivated in gardens or growing wild in Japan: hanashōbu (Iris ensata), kakitsubata (Iris laevigata) and ayame (Iris sanguinea). Of these three species, I. ensata is the one most commonly referred to as "Japanese iris" outside Japan.

The bluish purple color of the flowers of the Japanese garden iris is an example of the copigmentation phenomenon.

The (ハナショウブ, 花菖蒲^?, Iris ensata var. ensata, syn. I. ensata var. hortensis I. kaempferi) grows in the wet land and is the most extensively cultivated variety in Japanese gardens. According to the place where it was cultivated, it is classified into the Edo (Tokyo), Higo (Kumamoto Prefecture), Ise (Mie Prefecture), American (U.S.A.) and other series. It is extensively grown in gardens throughout the temperate zones. Several cultivars have been selected, of which 'Rose Queen' and 'Variegata' have gained the Royal Horticultural Society's Award of Garden Merit.

The (カキツバタ, 杜若^?, Iris laevigata) grows in the semi-wet land and is less popular, but is also cultivated extensively.

It is a prefectural flower of Aichi Prefecture due to the famous tanka poem which is said to have been written in this area during the Heian period, as it appears in The Tales of Ise by Ariwara no Narihira (note that the beginning syllables are "ka-ki-tsu-ha (ba)-ta"):

...
Wikipedia