Dense spike-primrose (Epilobium densiflorum) COSEWIC assessment and status report: chapter 3

Species Information

Name and classification

Scientific name:

Epilobium densiflorum (Lindl.) Hoch & Raven

Synonym:

  • Boisduvalia densiflora (Lindl.)Wats.
  • Oenothera densiflora Lindl

Common name:

Dense spike-primrose

Family:

Onagraceae (Evening Primrose Family)

Major plant group:

Dicot flowering plant

Description

Epilobium densiflorum is an annual herb with a taproot. Stems are 15-100 cm tall, simple or branched above, peeling below. Plants are densely white-hairy to long soft- or stiff-hairy, and sometimes glandular. Leaves are alternate, except near the base, lanceolate, becoming narrowly egg-shaped in the inflorescence, 1-8.5 cm long, entire or remotely fine-toothed, upper ones hairy; unstalked or nearly so. Flowers in a crowded inflorescence of densely-leafy, terminal and lateral spikes; hypanthium 1.5-4 mm long; petals 3-10 mm long, white to rose-purple and notched at the tip. Sepals 2-9 mm long. Stigmas generally entire, rarely 4-lobed. Fruits are capsules, more or less spindle-shaped, long-hairy, 0.4-1.1 cm long, very short-beaked, 4-chambered and splitting in the middle of each chamber when ripe. Seeds 3-6 per chamber, flat, 1.2-2 mm long, with a net-like surface texture, hairless and brown, and without tufts of hairs (Douglas and Meidinger 1999; Figure 1).

Epilobium densiflorum varies greatly throughout its range. Plants with shorter, paler petals and shorter, eglandular hairs than the nominal variety have been referred to as var. salicina; this variety is currently not recognized as a significant taxonomic entity (Kartesz 1999). Many older floras place E. densiflorum in the genus Boisduvalia (B. densiflora), which differs from Epilobium by lacking a tuft of silky hairs at the summit of each seed.

Epilobium densiflorum may be mistaken for E. torreyi, another rare species in British Columbia. The two species may occur together. Table 1 summarizes significant differences between the two species.

Figure 1. Illustration of Epilobium densiflorum: upper portion of plant (left); capsule (top right); flower (middle right). Illustration by J.R. Janish from Hitchcock and Cronquist 1973, with permission.

Figure 1. Illustration of Epilobium densiflorum: upper portion of plant (left); capsule (top right); flower (middle right). Illustration by J.R. Janish from Hitchcock and Cronquist 1973, with permission.

 

Table 1. Character comparison: Epilobium densiflorum vs. E. torreyi
Character Epilobium densiflorum Epilobium torreyi
Petal length 1-3 mm (2.5) 3–8 (12) mm
Capsules slenderly fusiform narrower
internal septa completely free from valves adherent to valves
Flowers crowded (inflorescence elongating in fruit) usually not crowded
Leaves lanceolate to ovate linear to narrowly lanceolate
Vestiture densely ashy-strigose to soft pilose, often glandular villous-pilose

From Scoggan 1978-1979.

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