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Iris missouriensis

Western Blue Flag, Rocky Mountain Iris
Perennials, Flowers


A large and remarkably diverse group of 200 to 300 species, varying in flower color and form, cultural needs, and blooming periods (although the majority flower in spring or early summer). Leaves are swordlike or grasslike. Flowers (fragrant, in many kinds) are showy and complex in structure.

Iris missouriensis

Native to 2,000–12,000-ft. elevations from western Nebraska and the Dakotas into the Sierra Nevada/Cascade mountain ranges and mountains of Southern California, and from the Yukon into northern Mexico. In zones where the plant is adapted, local forms are more likely to succeed. Narrow, flat, bluish green, winter-deciduous leaves range from 12–22 in. high. Blooms in late spring and summer; blossoms have narrow, upright standards and semiflaring to drooping falls, on stems a bit higher than the foliage. Colors range from lavender to white, with veins in darker lavender to purple; the darker colors are found in the more southerly and westerly forms. Give a sunny location and neutral to alkaline, water-retentive soil that is kept moist throughout growth and bloom, dry thereafter. The best time to plant or transplant is from early spring into the flowering period.

A similar species, I. longipetala, is considered by some botanists to be a form of I. missouriensis. It differs from I. missouriensis in its nativity (Northern and central California Coast Ranges, up to about 1,200 ft.) and in having evergreen foliage and an early-spring bloom period.

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