Lady Bird Johnson Wildflower Center - The University of Texas at Austin information

 Native Plant Database

Iris missouriensis

Rocky Mountain iris, Western blue flag

Iridaceae (Iris Family)

Iris missouriensis (Rocky mountain iris)
Smith, R.W.
Rocky Mountain iris is slender-stemmed and 1-2 ft. high. One to four flowers occur per stem. They are pale to dark, lilac-purple and haves yellow bases. The grayish-green leaves are relatively broad. Large, delicate, pale blue or blue-violet flowers, often with purple veins, bloom at the top of stout, leafless (or with 1 short leaf) stalks that grow from dense clumps of flexible, tough, sword-shaped leaves.

The only native species east of the Cascade Mountains and the Sierra Nevada, it often forms dense, large patches in low spots in pastures, where the tough leaves are avoided by cattle.

Image Gallery:

14 photo(s) available

Plant Characteristics

Duration: Perennial
Habit: Herb
Leaf: Green
Size Class: 1-3 ft.

Bloom Information

Bloom Color: Purple
Bloom Time: May , Jun


USA: AZ , CA , CO , ID , MN , MT , NE , NV , NM , ND , OR , SD , UT , WA , WY
Canada: AB , BC
Native Distribution: B.C. to s. CA (mostly e. of the Cascades), e. to the Dakotas, NM & Mex.
Native Habitat: Marshes; wet meadows; drier areas if moist until flowering time

Growing Conditions

Water Use: High
Light Requirement: Sun
Soil Moisture: Wet
CaCO3 Tolerance: High
Soil Description: Wet soils.
Conditions Comments: This iris spreads to form colonies. It needs to be divided regularly.


Use Wildlife: Hummingbirds
Warning: POISONOUS PARTS: Rhizomes (thickened roots) and rootstocks, fresh or dry. Minor skin irritation when touched, low toxicity if ingested. Symptoms include nausea, vomiting, abdominal pain, diarrhea, elevated temperature following ingestion; skin irritation upon contact with seeds, rootstock, or cell sap. Toxic Principle: Irisin, iridin, or irisine. (Poisonous Plants of N.C.)

Conspicuous Flowers: yes
Attracts: Hummingbirds

Last Update: 2015-03-17