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

Distribution

Global range

Epilobium densiflorum ranges from Vancouver Island and the southern Gulf Islands southward on both sides of the Cascades from Washington to California (rarer on the immediate coast and in the Central Valley) and northern Baja California; east to western Montana (extirpated), Idaho, Utah and Nevada (Scoggan 1978-1979, Hoch 1993, Hitchcock et al. 1961, Raven and Moore 1965). See Figure 2.

Figure 2. Global distribution of Epilobium densiflorum.

Figure 2. Global distribution of Epilobium densiflorum.

The nearest United States population is on San Juan Island in Washington State (Atkinson and Sharpe 1993), about 20 km from the nearest Canadian occurrence in Victoria.

Canadian range

In Canada, Epilobium densiflorumhas been reported from two widely separated locations: southwest British Columbia and south-central Alberta (Figure 3). The single record from Alberta is a historic 1911 collection at the Canadian Museum of Nature (CAN) made by M.O. Malte from the vicinity of Lethbridge (Scoggan 1978-1979; Michael J. Shchepanek pers. com. Dec. 16, 2002). This record is highly suspect and is here considered to reflect an error in locality labelling. It is dated August 27, 1911, but other herbarium records indicate Malte left Alberta sometime between August 3 (last known Alberta collection for that period) and August 7 (when he collected plants from Fernie, British Columbia). He subsequently collected material from Agassiz on August 18 and from Victoria on August 24 suggesting a single westbound trip. Malte was collecting in Alberta again, but not until 10 days later. Significantly, Malte’s collections on August 24 included a specimen of Epilobium densiflorum from Victoria (Ksenija Vujnovic pers. com. Dec. 16, 2002, Joyce Gould pers. com. Dec. 30, 2002, BCCDC Herb Database Dec. 27, 2002).

Apart from Malte’s questionable collection, Epilobium densiflorum has never been reported in Canada east of the Strait of Georgia (Ksenija Vujnovic pers. com. Dec. 16, 2002, Joyce Gould pers. com. Dec. 30, 2002). Although formerly known from Montana (where it has become extirpated) it was only found there once. The Montana specimen was collected in Sanders County, in a lowland area west of the Continental Divide (Montana Natural Heritage Program 2003). In conclusion, the balance of evidence suggests Epilobium densiflorum does not occur in Canada east of the Strait of Georgia.

The earliest collection was made by Macoun in 1887 from Departure Bay, Nanaimo. The total current and historical extent of occurrence (1887-present) in Canada (British Columbia) covers approximately 2,000 km², all within the Garry Oak Ecosystem. The current extent of occurrence is reduced to approximately 900 km². There is insufficient data to determine when most of the decline in the species’ range occurred. Most of the decline can be attributed to the loss of the Qualicum population (apparently between 1910 and 2001) although a significant component occurred as a result of the loss of the North Pender Island population between 1981 and 2001.

Figure 3. Canadian distribution of Epilobium densiflorum (solid black circles indicate extant populations; open circles represent extirpated populations).

Figure 3.  Canadian distribution of Epilobium densiflorum (solid black circles indicate extant populations; open circles represent extirpated populations).