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A genus of two species in western N. America, belonging to the same tribe of the Rose family as Dryas, Fallugia, and Cowania. Flowers solitary, almost sessile. Carpels one, rarely two, with a short curved, persistent style. Fruit an achene, crowned by the persistent style. The genus is named after F. Pursh, a botanist of German birth who is the author of Flora americae septentrionalis (1814), one of the first works on the flora of N. America.