Western Blue Flag (Iris missouriensis)

Western Blue Flag


  • Stands 30 to 60 centimetres (11.8 to 23.6 inches) tall.


  • Usually occur two to a stem; up to four flowers can grow on a stem.
  • Colour ranges from pale blue to blue-violet.
  • Each flower is made up of nine petal-like segments comprising three petals, three sepals (leaflike divisions located at the base of the flower) and three enlarged styles (stalklike part of a flower’s female reproductive organ).
  • Sepals are 4 to 6 centimetres (1.57 to 2.36 inches) long; they spread and curve downwards and are coloured with a yellow spot from which purple veins radiate.
  • Styles curve down over the sepals.
  • Petals form the inner segment of the flower and stand erect or arch upward.


  • Produces an oblong seed capsule about two to five centimetres (0.79 to 1.97 inches) long.
  • The seed capsule splits along three sides when it is mature, releasing dark brown seeds.


  • Pale blue-green in colour; about 10 to 40 centimetres (3.94 to 15.75 inches) long and 5 to 10 millimetres (0.20 to 0.39 inches) wide.
  • Leaves grow from the base of the plant and are folded in half lengthwise.
  • Western blue flag is the only species of iris native to Alberta.
  • Has a very limited distribution in the southwestern corner of Alberta, growing primarily in the foothills along the southeastern edge of the Rocky Mountains.
  • In Canada, outside of Alberta, introduced populations of western blue flag can be found in British Columbia.
  • In the United States, western blue flag is widespread in the western states, and can be found in portions of the Rocky Mountain states to the Great Plains, ranging from Montana south to Mexico.
Natural History


  • Prefers moist, level ground, particularly at the edges of wet meadows or seepage springs.
  • Can often be found close to willow thickets around moist depressions or minor drainages.

When Active

  • The western blue flag is a long-lived perennial (plant that lives for two or more years).
  • Prefers full sun.
Reproduction and Growth
  • Western blue flag populations can maintain themselves over long periods of time by growing out of a thick underground rhizome (or rootstock). The rhizome can withstand heavy trampling, and give rise to new plants when conditions are favourable.
  • Flowers are cross-pollinated by insects such as bees.
  • When seed capsule matures, it releases seeds when shaken by the wind or passing animals. The seeds fall close to the plant, ensuring they grow in a favourable habitat.
Conservation and Management


The Western Blue Flag is classified as At Risk in the General Status of Alberta Wild Species report. See:

In a more detailed status assessment, Alberta’s Endangered Species Conservation Committee identified the western blue flag as a Species of Special Concern—a species that without human intervention may soon become threatened with extinction. See information on the Endangered Species Conservation Committee and Species of Special Concern at:

Also see the Status of the Western Blue Flag in Alberta report at:


Factors that can limit the success of local western blue flag populations include:

  • Habitat loss, alteration and fragmentation due to human agricultural activities
  • Competition from non-native, introduced species such as smooth brome
  • Over-grazing of livestock in areas where western blue flag grows
  • Unfavourable levels of soil moisture due to drought or flood
  • Uprooting of rhizomes for human horticultural and medicinal uses
  • Use of agricultural herbicides in areas where local western blue flag populations exist

Current Management

In 1999, western blue flag was recommended for listing as a Threatened species under the Wildlife Act by Alberta’s Endangered Species Conservation Committee (ESCC).

A maintenance and recovery plan for western blue flag was developed and implemented. Subsequently, in 2005, primarily as a result of the discovery of several new, previously unknown populations, the species was downlisted to Species of Special Concern. For details, see:


Page Information

Updated: Mar 4, 2014