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Recovery Strategy for the Western Spiderwort (Tradescantia occidentalis) in Canada – 2013

2. Species Status Information

Western Spiderwort (Tradescantia occidentalis (Britt.) Smyth) is native to the interior plains and Colorado plateau of western North America. Globally, the plant is ranked as secure (G5; NatureServe 2010a). In Canada, Western Spiderwort is considered critically imperiled (N1; NatureServe 2010a) and was listed as threatened under the Species at Risk Act (SARA) in 2005. Alberta, Saskatchewan and Manitoba all list the species as critically imperiled (S1; NatureServe 2010a), and as “threatened” under their respective Endangered Species or Wildlife Acts. Western Spiderwort is more common in the United States, where it is considered nationally secure (N5?; NatureServe 2010a); however, it has not been ranked in 17 of the 18 states in which it occurs (SNR or SNA; NatureServe 2010a). No information is available on the abundance of Western Spiderwort in the United States. It is not known precisely what percent of the species’ global distribution and abundance currently is found in Canada, only that it is small and likely between 1 to 5% of the global extent of occurrence[1].

1 Extent of occurrence, as defined by COSEWIC, is “the area included in a polygon without concave angles that encompasses the geographic distribution of all known populations of a species” (COSEWIC 2010).