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COSEWIC assessment and status report on the Dense Spike-primrose (Epilobium densiflorum) in Canada



Epilobium densiflorumis an annual forb that flowers and fruits in mid- to late summer and probably germinates in the following spring.

Reproduction and dispersal

Epilobium densiflorum flowers in June through August. The species has been reported as predominantly autogamous (self-pollinated) and ovules may be fertilized by pollen from the same flower (Seavey 1992). In contrast, Raven (1979) reports that pollen is transferred primarily by bees and to a lesser extent by syrphid flies. Epilobium densiflorummay occur with the closely related E. torreyi. Experimental crosses between the two species only produce capsules 33% and 43% of the time and their mature progeny may be sterile (Seavey 1992).

The seeds of E. densiflorumare irregularly angular and fusiform (Raven 1976) and the seed surface cells are concave with radial walls that are longitudinally striate and irregularly thickened (Seavey et al. 1977). The loculicidal capsules dehisce in the late fall and the seeds probably fall to the ground as the capsules are shaken during winter rains (Raven 1976). Epilobium densiflorum lacks two critical characteristics that aid wind dispersal by seeds of other species in the genus: an obovoid, flattened shape and the presence of a coma (Raven 1976). Strings of populations present along drainages could possibly reflect dispersal by water; however, no such evidence has been found. It is unlikely that such events play any significant role in seed dispersal since the populations occur in wet areas with no external drainage and in sites that are merely saturated with water but not flooded.

There is no information on seed banks in this species. Many of the sites are waterlogged for extended periods during the fall, winter and spring when conditions are ripe for fungal growth and seed deterioration.

Germination and seedling ecology

Seeds germinate when there is abundant water and may be submerged for a time (Raven and Moore 1965; Raven 1976).


Although this species germinates in moist places it matures and reproduces under xeric conditions. This makes it well-adapted to survive the gradual onset of summer drought characteristic of southeast Vancouver Island.


There is no information on the physiology of Epilobium densiflorumthat is relevant to assigning at-risk status or developing recovery plans.