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Western Blue Flag

Western Blue FlagWestern blue flag (Iris missouriensis Nuttall) is the only species of Iris native to Alberta. It is widely distributed in the western United States but enters Canada only in Alberta where it is present along the southeastern flank of the Rocky Mountains. Western blue flag is restricted to the Foothills, Grassland and Parkland Subregions - areas that have been extensively modified by agriculture with few native tracts remaining. There are few native occurrences in the province and the species is ranked S1 by the Alberta Natural Heritage Information Centre. Western blue flag is also designated as threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC 1998).

In Alberta, western blue flag is restricted to the Foothills Fescue Grassland and Foothills Parkland Natural Subregions. The majority of native occurrences (distinct locations, where the species occurs) are in the Foothills Fescue Grassland and only one is in the Foothills Parkland, largely due to the climate of these regions. Ideal climates for growing western blue flag have been described as having cold, dry winters with moist springs and early summers followed by warm, dry, mid- to late summers. The western blue flag is a plant of moist meadows such as those found along freshwater shorelines and stream banks. The species is often found in areas with soils that dry out later in the summer. It is intolerant of permanently wet conditions and heavy shading. Native populations of western blue flag in Alberta occur on sites that are on level terrain or gentle slopes with moisture conditions where water is removed slowly enough to keep the soil wet for most of or a significant portion of the growing season. Many of the stands of western blue flag are in close proximity to willow thickets around depressions or drainages. Elevation for all of the known Alberta occurrences ranges from 914 to 1370 metres.

The principal vegetation composition of Alberta western blue flag sites appears to be transitional between the shrubby cinquefoil/rough fescue and the tufted hair grass habitat types of northern Montana. Kentucky bluegrass and inland bluegrass dominate at most of the Alberta sites. The habitat of the population at Police Outpost Provincial Park is being severely altered by an invasion of smooth brome. Native grasses that were dominating the site in 1987 are currently being out competed by the smooth brome.

Western blue flag is a member of the family Iridaceae . It is a perennial herb with thick (1 to 1.5 centimetres) rhizomes from which are produced tufts of leaves. The flowering stalks bear two to four showy flowers that range in colour from pale blue to deep blue or lavender. White flowered forms also occur but are rare. The flowers bloom sequentially rather than all at once. Flowering dates for western blue flag throughout its range are May through July. In Alberta, flowering occurs between mid-June and early July.

The fruit of Iris is a three-parted capsule that splits to release its globose, smooth-skinned seeds. The seeds can be dispersed either by wind or by water. Fruiting stems persist for one year or more. The Alberta populations of western blue flag have good seed set. Western blue flag grown at the Devonian Botanic Garden near Edmonton require a germination period of two to three months and flower production follows in two to three years.

Reprinted from Alberta Wildlife Status Report No. 21 (1999), with permission from Alberta Sustainable Resource Development.

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