Status of Lompoc Yerba Santa Eriodictyon capitatum (Namaceae): an Endangered Plant in Santa Barbara County, Southern California

Abstract

Lompoc yerba santa Eriodictyon capitatum (Namaceae) is an evergreen shrub endemic to west Santa Barbara County in coastal southern Calif. The species was listed as rare under the Calif. Endangered Species Act in 1979 and as endangered under the U.S. Endangered Species Act in 2000. At Federal listing in 2000, Lompoc yerba santa was known from four locations (five occurrences) in three geographic areas. In 2022, the species is known from 11 occurrences in four geographic populations of which 10 occurrences are considered extant and 1 occurrence likely extirpated: Orcutt Oil Field in the Solomon Hills, 2 occurrences; Burton Mesa on Vandenberg Space Force Base North, 6 occurrences; La Salle Canyon on Vandenberg Space Force Base South, 1 occurrence; and Santa Ynez Mountains, 2 occurrences. Lompoc yerba santa occurs mostly in chaparral and bishop pine (Pinus muricata) forest, and most occurrences are in sandy soil. The species stands up to 5 m tall and with vertical stems up to 10 cm diameter. Much of its reproduction appears to be vegetative by rhizome production, suggesting low dispersal ability, and it is a habitat specialist with apparent dependence on substrate disturbance and fire. Using all available information and international standards with a precautionary but realistic attitude to uncertainty, Lompoc yerba santa in 2022 meets IUCN criteria for endangered status: the small extent of occurrence is 433 km2 (<5,000 km2) and the small area of occupancy is 2.30 km2 (<10 km2), along with the geographic range being severely fragmented, and the quality of habitat is observed/inferred/projected to be in continuing decline (altered fire regime/fire management practices, climate change with severe drought and increased temperatures).