Slender collomia (Collomia tenella) COSEWIC assessment and status report: chapter 4

Distribution

Global range

Collomia tenella ranges from southwestern British Columbia, south in the western United States to Wyoming, Utah, Nevada and Oregon (Hitchcock et al. 1959; Figure 2). The nearest known location to the BC populations is in Washington state in Chelan County (University of Washington Vascular Plant Database, 2003) about 140 km to the south. It is not known how readily this species is dispersed over long distances, so United States populations should not be relied upon for rescue effect.

Figure 2. Distribution of Collomia tenellain North America.

Figure 2.  Distribution of Collomia tenella in North America.

Canadian range

In Canada, C. tenella is known only from the Princeton area in southwestern British Columbia (Figure 3; Pojar 1999; Douglas et al., 1998a, 2002a, b).

This species was discovered in British Columbia in 1997. It grows in a natural habitat type of eroded sand ridges with other native species in an undeveloped area, so it is unlikely that it was introduced to this site. Furthermore, the region has been generally under-collected so it was likely over-looked. Only one of the other 10 rare plant species that occur in the Princeton area was collected (on one other occasion) prior to 1996. The Princeton area may have been passed by many collectors who were en route from the coast to collecting destinations in the biologically rich Okanagan Valley further east. Another argument that favors this species as a native element is the existence of numerous taxa whose distribution follows a similar pattern in the Pacific Northwest with the northern limit of the species range in British Columbia. The shrub steppe and open forests of southern British Columbia are part of a much larger ecological unit that extends south to Washington, Oregon and other intermountain states.

Finally, in the Species at Risk Act (Section 2.2), it states that for the purposes of a wildlife species in subsection 1, "a species, subspecies or biologically distinct population is, in the absence of evidence to the contrary, presumed to have been present in Canada for at least 50 years" (Government of Canada 2003).  Therefore, since there is no support for the argument that it is a non-native species, it should be assumed native.

Frank Lomer was the first collector to intensively investigate this area. He has searched for new sites for this species ever since he found it in 1997 (Lomer, pers. com., 2003). He regularly collects throughout the interior of British Columbia in unique or interesting habitats with hopes of new discoveries and keeps an eye out for several rare species including Collomia tenella. He has found no other locations during this time. In both 2002 and 2003, he was contracted to do specific searches for new sites for the rare species known in the Princeton area. He surveyed the east side of the Similkameen River opposite the known sites and along the US border near Grand Forks, Anarchist Mountain, and Midway, but did not find any new sites.

Figure 3. Distribution of Collomia tenella in British Columbia.

Figure 3.  Distribution of Collomia tenella in British Columbia.

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