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(発色補助作用)phenomenon. (https://en.wikipedia.org/wiki/Japanese_iris)