Abstract
Chorro Creek bog thistle Cirsium fontinale var. obispoense (Asteraceae) is a biennial or short-lived perennial plant up to 2 m tall that occurs only in San Luis Obispo County, west of the outer coast ranges. It was listed as endangered under the California Endangered Species Act in 1993 and the U.S. Endangered Species Act in 1994. Chorro Creek bog thistle is a serpentine endemic, occupying perennial seeps and springs in serpentine soil and rock in western San Luis Obispo County from north of San Simeon Creek to south of the city of San Luis Obispo. At federal listing in 1994 Chorro Creek bog thistle was known from nine occurrences (one of these presumed extirpated) and with an estimate of
