Iris tectorum

What does Iris tectorum look like?

Iris tectorum is a low-growing perennial with thick, creeping rhizomes and floppy, sword-shaped leaves that form spreading clumps. Its flowers, 7–10 cm across, are usually lavender-blue, bluish-violet, or sky blue, with a white form also known. Each flower has three large, wavy-edged outer petals with mottled markings and a fringed white crest, and three smaller inner petals. The plant blooms in late spring or early summer, with each stem holding up to three flowers.

Where does Iris tectorum come from?

Native to central and southwestern China, as well as Korea and Myanmar, Iris tectorum was first described in the 19th century. It was discovered growing on the roofs of houses in Japan, which led to its common name 'roof iris'. The plant was introduced to Europe and the United States in the 1870s and has since naturalized in places like Bhutan, India, and parts of the US. It is found in meadows, forest edges, damp places, and beside water, often at elevations from 500 to 3,500 meters.

When and how Iris tectorum blooms

Iris tectorum grows from rhizomes planted just at the soil surface, spaced 20–30 cm apart. It prefers humus-rich, moist but well-drained soil, and light shade. The plant is usually propagated by division in spring or autumn, or from seed, which produces true-to-type plants. It is hardy in temperate climates and can be grown in borders, rock gardens, or containers. The plant blooms for about two weeks, with flowers appearing from April to June in the northern hemisphere and September to October in Australia.

How Iris tectorum is used

This iris is grown mainly as an ornamental in gardens and containers. Despite being toxic if eaten or handled, it has a history of use in Chinese herbal medicine, particularly for treating hepatitis and certain pains. In some traditions, fish are fed the plant as a remedy for stomach aches. The plant is also known for its cultural association with roofs in China and Japan, where it was once grown in thatch.

Kinds of Iris tectorum

There are several cultivars of Iris tectorum, including 'Alba' with white flowers, 'Burma Form' with dark violet blooms, and 'Variegata' with striped foliage and purple flowers. Other named forms include 'Wolong', 'Japan Form', and 'Taiwan Form', each with subtle differences in flower color, size, or leaf markings.

What Iris tectorum means

Iris tectorum is symbolic as the 'roof iris', reflecting its history of being grown on rooftops in China and Japan. In Japan, it is called Ichihatu, meaning 'first', as it is among the earliest irises to flower. The plant is recognized as an ornamental and has been featured in botanical publications since the 19th century. Its toxicity is noted in both horticultural and traditional contexts.

Where Iris tectorum is used and seen

BouquetA creative arrangement of flowers, given or displayed for many occasionsHakone Botanical Garden of WetlandsA garden of wetland and alpine plants in Hakone, JapanParc floral de ParisA botanical garden and flower park in the Bois de Vincennes, ParisParc Floral de la SourceA large public garden in Orléans built around the source of the Loiret riverKeukenhofA vast Dutch flower garden famous for its spring tulip displaysKanzashiTraditional Japanese hair ornaments, often crafted as folded silk flowersHanafudaJapanese playing cards with flower designs used for traditional gamesHistory of flower arrangementHow arranging flowers became an art across cultures and centuries

Questions people ask about Iris tectorum

Good reading and sources

• Iris tectorumRoyal Horticultural Society, Article
• USDA Plants DatabaseUS Department of Agriculture, Article
• Plants of the World OnlineRoyal Botanic Gardens, Kew, Plant database
• Where it has been recordedGBIF, Plant database
• Sightings and photos by naturalistsiNaturalist, Plant database

• Iris tectorum on WikipediaEncyclopedia
• More photos on Wikimedia CommonsPhotos
• Wikidata recordOpen data