Iris tectorum

Iris tectorum, also known as roof iris, is an Asian botanical species that has been cultivated for a long time on the thatched roofs of Japanese and Chinese houses. This rhizomatous perennial forms beautiful clumps of bright green foliage over time, which is evergreen in winter depending on the climate. Its large, flat iris flowers display a beautiful lavender-violet colour that stands out magnificently in partial shade, just like its spring green foliage. It is an elegant plant and quite easy to grow in humus-rich soil that is not too dry in summer. 

Iris tectorum belongs to the Iridaceae family and to the group of beardless, crested irises. It is probably native to China, Korea, and Japan. In the wild, it is found up to 3,500m (11483ft) altitude, mainly in clear undergrowth, but also along riverbanks. It can also be observed in China along roadsides and on steep slopes. It prefers dry winters and long, hot, and humid summers, but adapts wherever summers are well marked. It is a perennial plant with thick and creeping rhizomes that forms a clump up to 45cm (18in) tall when in flower, with a theoretically unlimited spread. The leaves are sword-shaped, flexible, bright green, and arranged in fans. They persist in winter if it is not too cold. In dry summers, the plant goes dormant and its foliage dries up. Flowering generally occurs in May. Branched cylindrical flower stalks emerge from the foliage, each one bearing 1 to 3 flowers. The flowers are 8 to 10cm (3 to 4in) wide. Each one consists of 3 large sepals with an erect and fringed crest and 3 smaller inner petals. The sepals are a vivid mauve speckled with violet and veined with white towards the throat.  

The roof iris is a beautiful plant for partial shade or non-burning sun. It is versatile and easier to pair than garden irises. It is elegant in undergrowth, superb near water features, highly decorative in a naturalistic bed, and unique in a slightly cool rockery. It can be paired with periwinkles, Caucasian forget-me-nots, dead nettles, bergenia, epimediums, and bigroot geraniums. Beside water features, it can accompany Siberian iris and female fern. for example. This iris is grown like Japanese iris.