Flower profile

Western blue flag

Iris missouriensis

Western blue flag (Iris missouriensis) is a flowering plant in the Iridaceae family, native in the lower 48 states, blooming mostly May–July across the U.S.

Native in the lower 48

Western blue flag is a wildflower that USDA PLANTS lists as native in the lower 48 states. It's on our flower lists for 4 states, and across the U.S. it's most often seen in bloom in May–July.

15states where USDA records it

4Bloomipedia state lists include it

10,686U.S. sightings*

*iNaturalist research-grade observations, as of October 17, 2026.

On our lists for: Colorado, New Mexico, South Dakota, Wyoming

Quick look

Iris missouriensis is a hardy flowering rhizomatous species of the genus Iris, in the family Iridaceae. Its common names include western blue flag, Rocky Mountain iris, and Missouri flag.
From Wikipedia's article Iris missouriensis, CC BY-SA 4.0.

It belongs to the Iridaceae family. ^iNaturalist
USDA PLANTS describes it as an herb (forb) with a perennial life cycle. ^{USDA PLANTS}
USDA PLANTS lists it as native in the lower 48 states and records it in 15 states. ^{USDA PLANTS}
NatureServe lists it as native to Colorado, New Mexico, Wyoming and South Dakota. ^NatureServe
In Colorado, most iNaturalist sightings of it in flower come in May–June. ^iNaturalist
In New Mexico, most iNaturalist sightings of it in flower come in May–June. ^iNaturalist
USDA PLANTS lists its flower color as purple. ^{USDA PLANTS}
USDA PLANTS gives its bloom period as spring. ^{USDA PLANTS}
USDA PLANTS lists a mature height of about 1 ft. ^{USDA PLANTS}
iNaturalist has 3,006 research-grade sightings of it in Colorado, ranking #47 among the 160 flowers on our Colorado list. ^iNaturalist
iNaturalist has 1,442 research-grade sightings of it in New Mexico, ranking #27 among the 152 flowers on our New Mexico list. ^iNaturalist
iNaturalist has 355 research-grade sightings of it in Wyoming, ranking #82 among the 113 flowers on our Wyoming list. ^iNaturalist

When does it bloom?

Flowering records by month across the U.S. (iNaturalist research-grade observations marked “Flowering”) (584 records)

Bloom time in the 4 states whose Bloomipedia list includes it

State	Type	Peak bloom	Sightings*
Colorado	Native	May–June	3,006
New Mexico	Native	May–June	1,442
Wyoming	Native	few records (17)	355
South Dakota	Native	few records (11)	312

Conservation status

Federal (U.S. ESA): Not listed Not listed under the Endangered Species Act. USFWS ECOS does track it with the label “Species of Concern,” which is informal and gives no legal protection. ^{USFWS ECOS}
NatureServe global: GNR Not yet ranked worldwide. ^NatureServe
Colorado: No list Colorado has no state law listing endangered or threatened plants, so we show NatureServe's Colorado ranks instead. NatureServe: SNR, not yet ranked in Colorado.
New Mexico: Not listed Not on New Mexico state endangered plant species (19.21.2.9 NMAC). NatureServe: SNR, not yet ranked in New Mexico. ^{19.21.2.9 NMAC}
Wyoming: No list Wyoming has no state law listing endangered or threatened plants, so we show NatureServe's Wyoming ranks instead. NatureServe: S4, apparently secure in Wyoming.
South Dakota: No list South Dakota's endangered and threatened list (ARSD 41:10:02) covers animals only, so we show NatureServe's South Dakota ranks for plants. NatureServe: SNR, not yet ranked in South Dakota.
Rare elsewhere: No other U.S. state ranks it S1, S2, SH or SX.

Checked October 17, 2026. Rankings and lists can change, so follow the links for the latest.

Can you eat it?

For peopleNot well documented

None of the sources we checked (NC State Extension (no page for this plant), USDA PLANTS) say whether it's edible or poisonous for people.

For petsToxic to dogs, cats and horses

ASPCA's entry “Flag” (Iris species), which covers the whole genus, lists it as toxic to dogs, cats and horses. Signs include: Salivation, vomiting, drooling,lethargy, diarrhea. Highest concentration in… ^ASPCA

🌿 Never eat a wild plant unless you're certain of its ID; this isn't medical advice. Worried about a person? Call Poison Control at 1-800-222-1222. Worried about a pet? Call your vet.

Where does it grow?

USDA PLANTS records Western blue flag in 15 states.

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recorded by USDA PLANTS on our state lists not recorded

See the full list of states

Arizona, California, Colorado, Idaho, Minnesota, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oregon, South Dakota, Utah, Washington, Wyoming.

Colorado counties with USDA records: Alamosa, Boulder, Conejos, Custer, Delta, El Paso, Elbert, Garfield, Grand, Gunnison, Huerfano, Jackson, Jefferson, La Plata, Lake, Larimer, Las Animas, Mesa, Mineral, Moffat, Montezuma, Park, Pitkin, Rio Grande, San Juan, San Miguel, Summit, Teller.

New Mexico counties with USDA records: Bernalillo, Catron, Cibola, Colfax, Lincoln, Los Alamos, McKinley, Mora, Rio Arriba, San Juan, San Miguel, Sandoval, Santa Fe, Socorro, Taos, Valencia.

Wyoming counties with USDA records: Albany, Big Horn, Carbon, Converse, Crook, Fremont, Hot Springs, Laramie, Lincoln, Natrona, Park, Sublette, Sweetwater, Uinta, Weston.

Growing conditions

USDA PLANTS gives Western blue flag a medium shade tolerance, low drought tolerance and high moisture use. It is rated for soil pH 7.0 to 8.5 and winter lows down to -28 °F.

Shade tolerance: Medium
Drought tolerance: Low
Moisture use: High
Soil textures it is adapted to: coarse, medium, fine
Soil pH range: 7.0 to 8.5
Minimum temperature tolerated: -28 °F
Frost-free days needed (minimum): 115
Annual precipitation range: 24 to 35 inches
Minimum root depth: 6 inches
Salinity tolerance: None
Fertility requirement: Low
Growth rate: Rapid
Lifespan: Short
Active growth period: Summer
Fruit or seed: Black · Summer to Spring
Can be propagated by: bare root, bulb, corm, seed
Commercial availability: Routinely Available

From the USDA PLANTS characteristics data for IRMI. USDA ratings are general guidance for the species, not a guarantee for your garden.

Names, range and relatives

Native status by region (USDA PLANTS): Canada: Native; Lower 48 states: Native.

Other scientific names (synonyms in USDA PLANTS): Iris longipetala, Iris pariensis, Iris tolmieana.

County records: USDA PLANTS lists it in 188 counties across 14 states; the most are in California (33), Colorado (28), Idaho (20).

Other Iris on Bloomipedia (11): Irises, Yellow iris, Dwarf crested iris, Douglas iris, Northern blue flag iris, Southern blue flag, Oregon iris, Dwarf iris, Beach-head iris, Dwarf lake iris.

More from the Iridaceae family (14 on Bloomipedia; most observed first): Western blue-eyed grass, Blue pigroot, Grasswidow.

More Colorado flowers

Great mullein

Verbascum thapsus

Introduced

🌼 Blooms in CO: July–October

Blue columbine

Aquilegia coerulea

★ CO state flowerNative

🌼 Blooms in CO: June–August

Showy milkweed

Asclepias speciosa

Native

🌼 Blooms in CO: June–July

Sources

USDA, NRCS. PLANTS Database, profile IRMI.
iNaturalist, Iris missouriensis: taxonomy, research-grade observation counts and “Flowering” annotations, retrieved October 17, 2026.
Wikipedia, Iris missouriensis (lead quoted under CC BY-SA 4.0).
Colorado: Colorado noxious weed lists A, B and C (8 CCR 1206-2, eff. May 15, 2025).
New Mexico: New Mexico state endangered plant species (19.21.2.9 NMAC).
New Mexico: New Mexico Noxious Weed List (NM Department of Agriculture, updated June 2020).
Wyoming: Wyoming state designated noxious weeds (W.S. 11-5-102(a)(xi)), as listed by the Wyoming Weed & Pest Council.
South Dakota: South Dakota statewide noxious weeds (ARSD 12:62:03:01.06).
USFWS, ECOS species database (ESA listing check), October 17, 2026.
NatureServe Explorer, Iris missouriensis (global and state ranks).
Edibility and toxicity: ASPCA.
Photo: Deniz Wilson via iNaturalist · CC0 · resized.