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Montana Field Guides

Dense Spike-primrose - Epilobium densiflorum
Other Names:  Boisduvalia densiflora

Potential Species of Concern
Native Species

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

Agency Status
MNPS Threat Rank:

External Links

State Rank Reason (see State Rank above)
Known from one historical collection in Sanders County from 1938.
General Description
Dense Spike-primrose is an annual with simple or branched stems that are 5-30 cm high. The sessile lower leaves are narrowly lance-shaped and 15-30 mm long with entire or sparsely-toothed margins, while the upper leaves are shorter and broader. Foliage is covered with soft, white, short or long hairs and may also be glandular. Flowers are borne in the axils of the upper leaves in dense spike-like inflorescences at the branch tips. Each flower has 4 pink to purple, 2-lobed petals, 2-8 mm long, and a 4-lobed calyx borne on top of the seed-bearing ovary. The 4-celled ovaries develop into straight, club-shaped capsules, 6-10 mm long, with 12-24 naked seeds.

Flowering in July or August.

Diagnostic Characteristics
Epilobium pygmaeum has petals 1.5-4 mm long and capsules that are slightly curved with 24-56 seeds. Species of Gayophytum have 2-celled ovaries, other species of Epilobium have seeds with tufts of hair at the tips, and Clarkia have stalked flowers.

Species Range

Range Comments
BC, MT, south to CA, UT, Mexico; one collection from Sanders County (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 4

(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 wet soil, often around ponds in the valleys.

  • 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.
    • Raven, P.H. and D.M. Moore. 1965. A revision of Boisduvalia (Onagraceae). Brittonia 17:238-254.
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Citation for data on this website:
Dense Spike-primrose — Epilobium densiflorum.  Montana Field Guide.  .  Retrieved on , from