Montana Field Guide

Western Pearl-flower is a slender annual with lax to erect, simple or sparingly branched stems that are 5-30 cm tall. The broadly spade-shaped, alternate leaves are up to 1 cm long, have toothed margins, and tend to clasp the stem. The foliage is glabrous, or there may be some short, stiff hairs on the stems and leaf margins. The single flowers are sessile in the axils of upper leaves, or bracts. Each flower has a calyx of 5 partly united, spreading-hairy, toothed lobes and a blue, 5-lobed corolla that is 3-6 mm long. Flowers on the lower are cleistogamous. The fruit is a short, broad capsule with numerous tiny seeds.

Flowering June-July, fruiting June-August.

Triodanis perfoliata is similar, but it has a glabrous calyx and occurs in drier habitats.

Vernally moist grassland slopes, mossy ledges, and riparian swales in valley, foothills and montane zones.

STATE THREAT SCORE REASON
Reported threats to Montana's populations of Western Pearl-flower are those encountered in its seasonally wet habitat at a range of elevations (MTNHP Threat Assessment 2021). Negative impacts from noxious species including Common St. John's-wort (Hypericum perforatum), Spotted Knapweed (Centaurea stoebe), and Cheatgrass (Bromus tectorum) are found at some populations. Other populations found along trails and one at a popular campground are at risk of damage during construction and maintenance of recreation areas, as well as continuous exposure to activities. Some population damage has likely occurred following maintenance actions. Trampling by hikers is found at some populations, and more severe disturbance from off-road vehicles is found at another. Threats from noxious weeds are likely amplified by ground disturbance and travel known for recreation areas.