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Slender-fruited Willowherb - Epilobium leptocarpum

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Native Species

Global Rank: G5
State Rank: SNR

Agency Status


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General Description
Delicate perennials, 8-30 cm tall; small basal or subsurface turions present; gemmae sometimes in upper leaf axils; stems glabrous (or strigillose above) but with lines of hairs decurrent from petioles. Petioles 3-5 mm below but leaves becoming sessile above. Leaf blades 0.8-4 cm long, narrowly lanceolate to elliptic, glabrous or sparsely hairy on margins; margins entire below but becoming denticulate above. Inflorescence nodding to nearly erect. Sepals 2.9-4 mm long, narrowly lanceolate, strigillose; petals 4-6.5 mm long, white fading to pink. Ovary densely strigillose; style to nearly 4 mm long; stigma broadly clavate. Capusle 2.5-5.5 cm long, 1-2 mm wide, sparsely strigillose. Seeds 0.8-1.2 mm long, papillose, coma 3.5-6.5 mm long, brownish, persistent (adapted from: Hoch, 1994, in Flora of Alberta, 2nd ed., revised).

Diagnostic Characteristics
Epilobium leptocarpum resembles Epilobium ciliatum but has a dull brownish coma (tuft of hairs on the seed) (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Range Comments
Kartesz (in prep. 2012) shows the species as having a highly irregular and spotty distribution in the US from WA and OR, CO, MT (Glacier and Meaghre counties), Fremont County (ID), and San Juan County (NM).

Moist open stony slopes (Hoch, 1994, in Flora of Alberta, 2nd ed., revised).

The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus bifarius, Bombus centralis, Bombus fervidus, Bombus flavifrons, Bombus frigidus, Bombus melanopygus, Bombus mixtus, Bombus rufocinctus, Bombus sylvicola, Bombus ternarius, Bombus sitkensis, Bombus occidentalis, Bombus griseocollis, Bombus impatiens, Bombus insularis, Bombus suckleyi, and Bombus kirbiellus (Thorp et al. 1983, Mayer et al. 2000, Colla and Dumesh 2010, Wilson et al. 2010, Colla et al. 2011, Koch and Strange 2012, Koch et al. 2012, Pyke et al. 2012, Williams et al. 2014).

  • Literature Cited AboveLegend:   View Online Publication
    • Colla, S., L. Richardson, and P. Williams. 2011. Bumble bees of the eastern United States. Washington, DC: USDA Forest Service, Pollinator Partnership. 103 p.
    • Colla, S.R. and S. Dumesh. 2010. The bumble bees of southern Ontario: notes on natural history and distribution. Journal of the Entomological Society of Ontario 141:39-68.
    • Koch, J., J. Strange, and P. Williams. 2012. Bumble bees of the western United States. Washington, DC: USDA Forest Service, Pollinator Partnership. 143 p.
    • Koch, J.B. and J.P. Strange. 2012. The status of Bombus occidentalis and B. moderatus in Alaska with special focus on Nosema bombi incidence. Northwest Science 86:212-220.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • Mayer, D.F., E.R. Miliczky, B.F. Finnigan, and C.A. Johnson. 2000. The bee fauna (Hymenoptera: Apoidea) of southeastern Washington. Journal of the Entomological Society of British Columbia 97: 25-31.
    • Pyke, G.H., D.W. Inouye, and J.D. Thomson. 2012. Local geographic distributions of bumble bees near Crested Butte, Colorado: competition and community structure revisited. Environmental Entomology 41(6): 1332-1349.
    • Thorp, R.W., D.S. Horning, and L.L. Dunning. 1983. Bumble bees and cuckoo bumble bees of California (Hymenoptera: Apidae). Bulletin of the California Insect Survey 23:1-79.
    • Williams, P., R. Thorp, L. Richardson, and S. Colla. 2014. Bumble Bees of North America. Princeton, NJ: Princeton University Press. 208 p.
    • Wilson, J.S., L.E. Wilson, L.D. Loftis, and T. Griswold. 2010. The montane bee fauna of north central Washington, USA, with floral associations. Western North American Naturalist 70(2): 198-207.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2022. Manual of Montana Vascular Plants, Second Edition. Fort Worth, TX: BRIT Press. viii + 779 p.
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Citation for data on this website:
Slender-fruited Willowherb — Epilobium leptocarpum.  Montana Field Guide.  .  Retrieved on , from