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Montana Field Guide

Montana Field Guides

Western Pearl-flower - Heterocodon rariflorum

Species of Concern
Native Species

Global Rank: G5
State Rank: S2
(see State Rank Reason below)

Agency Status
C-value: 7


External Links

State Rank Reason (see State Rank above)
Over a dozen known occurrences, including a half-dozen moderate to large-sized populations, a few small populations and several occurrences that need further survey work to document population sizes. Most populations are on National Forest lands. Invasive weeds infest several populations and are likely infest others. Hiking and ORV trails occur though or adjacent to a few populations and associated use may impact H. rariflorum plants.
General Description
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.

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

Species Range
Montana Range


Range Comments
Southern BC, ID, and northwestern MT to CA, NV, and WY. Sparse.

Observations in Montana Natural Heritage Program Database
Number of Observations: 72

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

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

This species has a Predicted Suitable Habitat Model available.

To learn how these Models were created see

Threats or Limiting Factors
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.

  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • Schassberger, L.A. 1991. Rare plant inventory of the East Pioneer Mountains. Prepared for the USDA Forest Service, Region 1, Beaverhead National Forest. Montana Natural Heritage Program, Helena, MT. 55 pp.
    • Schassberger, L.A. and J.S. Shelly. 1990. Sensitive plant surveys in the Bull River and adjacent drainages, USDA Forest Service, Region 1, Kootenai National Forest. Unpublished report. Montana Natural Heritage Program, Helena, MT. 60 pp.
    • Shetler, S.G. and N.R. Morin. 1986. Seed morphology in North American Campanulaceae. Annals Missouri Bototanical Gardens 73(4): 653-688.
  • Web Search Engines for Articles on "Western Pearl-flower"
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Citation for data on this website:
Western Pearl-flower — Heterocodon rariflorum.  Montana Field Guide.  .  Retrieved on , from