アヤメ科アヤメ属の多年草で、学名は Iris ensata var. spontanea (syn. Iris ensata var. ensata)。英名は Japanese water iris。
The Japanese water iris (Iris ensata var. spontanea) belongs to Iridaceae (the Iris family). It is a perennial herb that is native to Japan, as well as the Korean Peninsula, northeastern China and eastern Siberia. This herb grows in grasslands, marshes of mountains and fields, and can reach 50-120 cm in height. The leaves are lance-shaped and have conspicous midribs. The blue-purple flowers come in June to July. The flowers have yellow necta guides on the outer tepals. In Chinese, it is called "玉蝉花" (yu chan hua).