Contorted-pod evening-primrose (Camissonia contorta) COSEWIC assessment and status report: chapter 4

• Previous page
• Table of contents
• Next page

Distribution

Global range

Camissonia contorta ranges from British Columbia to California, east to Idaho and western Nevada (Figure 2).

NatureServe reports Camissonia contorta for Vermont but this is based on record(s) of Oenothera cruciata Nutt. var. sabulonensis Fern. (B. Popp pers. comm. 2003). This biennial or short-livedperennial, in the section Euoenothera of the genus Oenothera, now most commonly called Oenothera parviflora L. (Kartesz 1999), is a common plant in eastern Canada and the northeastern United States. It is a very different taxon from O. cruciata (S. Wats.) Munz (a synonym for Camissonia contorta).

Canadian range

In Canada, Camissonia contorta has a restricted distribution occurring only near sea level, in the Georgia Basin (Figure 3). It is restricted to the Coastal Douglas-fir biogeoclimatic zone.

It is known from eight populations according to COSEWIC standards, based on a minimum separation of about 1 km, seven extant and one historic. The extant populations include two on Savary Island in the Straight of Georgia, four on the Saanich Peninsula and nearby offshore islands near Victoria, and one southwest of Victoria (Figure 3). The Canadian distribution is heavily fragmented: the northern pair of populations is more than 150 km from the others and southwestern population is more than 30 km from its nearest neighbour. This fragmentation is largely a result of natural features. The intervening areas consist of marine environments, forested ecosystems or unsuitable substrates (non-sandy). Heavy residential development in the southern portion of the Canadian range has overlain an anthropogenic level of fragmentation. The Canadian population, plus a single nearby population on San Juan Island (Washington State) is widely disjunct from the species’ main range. The Canadian range constitutes less than 1% of the species global distribution.

Currently the plants occur over an area measuring approximately 1,500 km². Approximately 50% of this area is open ocean, so the effective extent of occurrence is generously estimated at about 750 km². A more realistic estimate, discounting obviously unsuitable habitat such as areas over 20 m asl or sites lacking sandy soils, would reduce the area of occurrence to much less than 50 km². The current area of occupancy (Table 2) totals 78,400 m² (= 7.8 ha = 0.0784 km²).