Brook spike-primrose (Epilobium torreyi) COSEWIC assessment and status report: chapter 6
Biology
General
Epilobium torreyi is an annual forb (herbaceous flowering plant) that flowers and fruits in mid- to late summer and probably germinates in the following autumn or winter.
Reproduction and dispersal
The species flowers in June and July (Hitchcock et al. 1961). Most flowers are cleistogamous, self-pollination occurring in the bud before the flower opens (Raven 1979).
The seeds of E. torreyi are 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 fall to the ground probably as the capsules are shaken during winter rains (Raven 1976). Epilobium torreyi lacks two critical characteristics that aid wind dispersal by seeds of most other species in the genus: an obovoid, flattened shape and a coma (Raven 1976). The scarcity of herbarium collections suggests that Epilobium torreyi has been a scarce species within its Canadian range since the early days of European settlement, despite the unexceptional nature of the habitats where it has been found.
Germination and seedling ecology
Seedlings have glabrous, round, opposite connate leaves similar to other Epilobium species. Seeds germinate when there is abundant water and may be submerged for a time (Raven and Moore 1965; Raven 1976). The genus requires light for germination and can germinate over a range of temperatures (Baskin and Baskin 1998). As for other native annual willowherbs, seed germination would occur in the autumn or winter unless the seeds become buried and subsequently become part of the seed bank (Grimes 1981).
Physiology
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 other information on the physiology of Epilobium torreyi that is relevant to assigning at-risk status or developing recovery plans.
Adaptability
This species is not known in the horticultural trade and there has been no research on the artificial propagation or seed germination for the species.