Status of the Endangered Chorro Creek Bog ThistleCirsium fontinalevar.obispoense(Asteraceae) in Coastal Central California

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 <3,000 individuals. In 2016 the conservation status of Chorro Creek bog thistle is substantially improved because of an increased number of known occurrences along with an increased number of occurrences that are protected. Only two of nine known occurrences were protected in 1994, whereas 10 of 21 occurrences are protected in 2016. There are many other locations with habitat that have not been searched, in particular on private land. It is highly likely that additional unknown occurrences exist in San Luis Obispo County, and possibly also in Monterey County to the north and Santa Barbara County to the south. In consideration of the available information, we conclude that Chorro Creek bog thistle is still endangered. However, when using the international standards of IUCN, we assign the category data deficient because of the limitations of our data.