Montana Field Guide

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.

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.

Vernally wet soil, often around ponds in the valleys.

POLLINATORS
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).