Short-rayed alkali aster (Symphyotrichum frondosum) COSEWIC assessment and status report: chapter 4

Distribution

Global range

Globally this species is known only from the United States, Mexico and Canada (Figure 2), from AZ, CA, CO, ID, MT, NV, NM, OR, UT, WA, WY (USDA  2002), Northern Baja California (Houle 1988) and BC (Douglaset al. 1998).  A report of the species (the synonym Brachyactis frondosa) from Maine (NatureServe 2004) is most likely an erroneous report.

Figure 2. North American distribution of Symphyotrichum frondosum. (Distribution information generalized from Houle 1988, Figure 1).

Figure 2.  North American distribution of Symphyotrichum frondosum

Canadian range

In Canada, Symphyotrichum frondosum is known only from British Columbia where it has been found primarily on lakeshores in the bunchgrass zone in the Southern Okanagan Valley (Douglas et al. 1998).  It is confirmed at four stations, one each at Osoyoos Lake, Vaseux Lake, Skaha Lake and Max Lake (Penticton).  The Osoyoos Lake station supports four sub-populations: one confirmed sub-population, one extirpated sub-population, and two unconfirmed sub-populations.  An ephemeral, disjunct population was reported from Surrey along the shore of the Fraser River in river dredgings. This site is now extirpated; however, Lomer (1996, 2001) feels that this indicates that the species most likely occurs upstream in the Fraser-Thompson drainage.

Figure 3.  Distribution of Symphyotrichum frondosum in British Columbia, Canada.  Note that the extirpated, ephemeral Surrey population has not been mapped. 

Figure 3.  Distribution of Symphyotrichum frondosum in British Columbia, Canada

This species was first collected in BC by Eastham in 1939 from the edge of Osoyoos Lake.  In his Supplement to the Flora of Southern British Columbia (1947), he reports it from Penticton and Osoyoos.  This may or may not be the same location as the Max Lake (Penticton) population, but Baumbrough (pers. comm. 2005) suspects it may represent plants at the south end of Lake Okanagan, a site that has since been developed.

In 1992, Lomer rediscovered S. frondosum on Osoyoos Lake and made a collection in 1993 (Lomer collection # 93-281, UBC).  This site was confirmed by Douglas in 1995 (Douglas collection # 13081, V) and lastly by Lomer in 2000 (Lomer collection # 3908, UBC).  Two new populations for Canada were reported by Lomer in 1999, one at Vaseux Lake (Lomer collection # 99-260, UBC) and another at Skaha Lake (Lomer collection # 99-263, UBC).  A new sub-population on Osoyoos Lake is reported in this report (photo documentation). 

The disjunct Surrey population was discovered by Lomer in 1994 (Lomer collection # 94-228 UBC?).  The voucher specimen cannot be located at this time; however, it was verified by J. Semple from WAT as S. frondosum (Lomer 2001). While this may be an accidental occurrence, Lomer (1996) believes this species is almost certainly found in the Fraser River drainage.  Populations in Washington State are found from Cowlitz County in the west to Spokane in the east, which indicates that it may be found in BC outside the Okanagan area.

A station reported for this species on Vancouver Island (Klinkenberg 2004) is based on a collection by Krajina in 1960, but was annotated by Lomer in 1993 to A. chilensis.

The extent of occurrence is approximately 56 km². The combined area of occupancy is 900 m², but the area of occupancy for several sites is unknown.

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