Herbs to 60 cm tall.
Roots fleshy; rhizomes freely branching, stout, covered with old leaf bases.
Stems unbranched or up to 2-branched.
Leaves basal leaves light green, usually white basally or sometimes purplish, 3–12 mm wide, glaucous; cauline leaves similar to basal.
Inflorescences 2–3-flowered; bracts keeled, outer usually shorter than inner.
Flowers perianth blue, lavender, or white, veined deeper violet; sepals deeply veined lilac-purple, with yellow-white signal at base of limb; claws yellowish white, veined and dotted with purple; floral tube less than 12 mm; style tips rounded, margins irregularly toothed; stigmas 2-lobed.
Fruits round in cross section, with 6 ridges.
Seeds globular to pear-shaped, light brown, wrinkled.
2n=38.
Wet meadows, roadside ditches, margins of streams. Flowering May–Jul. 300–2000 m. BR, BW, Col, ECas, Lava, Owy. CA, ID, NV, WA; north to British Columbia, northeast to MN and southeast to NM, south to Mexico. Native.
The leaves of I. missouriensis are unpalatable to livestock, and the species is considered a noxious weed in pastures. This species is morphologically variable across its large geographic range.
From late spring to early summer, slender buds above sword-shaped leaves unfurl into beautiful flowers. Petals in pale shades of blue or lavender have deep purple veins and a glowing yellow signal along its sepal midlines to guide insects to their reward. Many pollinators, including native bees and hummingbirds, are attracted to the nectar of Rocky Mountain iris. Plant this hardy rhizomatous species in a woodland garden or on moister parts of a wildflower meadow.
as described under Iris missouriensis
Rhizomes freely branching, producing large colonies, stout, 2-3 cm diam., clothed with dark remnants of old leaves; roots fleshy. Stems simple or 1-2-branched, solid, 2.5-6 dm. Leaves: basal with blade light green, often white basally, not prominently veined, linear, 4.5-6 dm × 0.3-1.2 cm, glaucous, apex acute; cauline 2-3, often shed with spent stem, similar to basal leaves, distal may subtend branch. Inflorescences with terminal and lateral units (when present) (1-)2-3-flowered; spathes subopposite to distant, to as much as 3-7.5 cm apart, lanceolate or ovate, keeled, outer usually shorter, 3.5-4 cm, inner 5.5-7 cm, scarious with herbaceous areas basally and along keel, apex acuminate. Flowers: perianth blue to lavender to white, veined deeper violet; floral tube green with purple veins in line with midrib of petals, funnelform, constricted above ovary, 0.5-1.2 cm; sepals deeply veined lilac-purple, with yellow-white signal at base of limb, claw yellowish white, veined and dotted with purple, obovate, 3.7-7 × 1.2-3.2 cm; petals slightly divergent, oblanceolate to spatulate, 3.6-7 × 0.5-1.2 cm, base gradually attenuate, apex acuminate or rarely emarginate; ovary trigonal with 6 shallow ridges, 1-2 cm; style 2.4-4 cm, crests quadrate, 0.7-1.4 cm, margins irregularly toothed; stigmas 2-lobed, margins entire; pedicel slender, 1-6 cm at anthesis, increasing to 7.5-8 cm at maturity. Capsules almost circular in cross section, with 6 obvious, equidistant ridges, 4-5 × 1.5 cm. Seeds light brown, nearly globular to pyriform, 4-4.5 mm, wrinkled. 2n = 38.Flowering May--Jul. Wet meadows, roadside ditches, margins of streams; 10--3000 m; Alta., B.C.; Ariz., Calif., Colo., Idaho, Mont., Nebr., Nev., N.Mex., Oreg., S.Dak., Utah, Wash., Wyo.; n Mexico.The ecological range of Iris missouriensis is probably more varied than that of any other North American species of the genus, extending from almost sea level in southern California to 3000 m in Montana and Wyoming. There is correspondingly wide variation in a number of characters, which has caused much confusion as to taxonomic circumscription. Homer Metcalf (pers. comm.) made a detailed study of this species. The basic requirement for its success seems to be an extremely wet area before flowering and then almost desertlike conditions for the rest of the summer. In large populations, sometimes covering hundreds of acres, Iris missouriensis may be found with either simple or branched stems, leaves from 4 mm to more than 1 cm wide, shorter than the stem or longer, only one flower to as many as three on a stem, and colors from deep blue to almost pure white. A single plant found on the Pariah Plateau in Kane County, Utah, with leaves only 3-4 mm wide and a single flower stem only 4 cm long, which meant that the flower was at almost ground level, was named Iris pariensis. No other such specimen has been located, and this entity must be considered as just an aberrant form that was due to the desertlike conditions in which it was growing.Iris missouriensis is known to hybridize with I. longipetala.