Status of the Endangered Indian Knob Mountainbalm Eriodictyon altissimum (Namaceae) in Central Coastal California

Abstract

Abstract. Indian Knob Mountainbalm Eriodictyon altissimum (Namaceae) is a shrub endemic to western San Luis Obispo County in central coastal California, and little has been published regarding it. The species was listed as endangered under the California Endangered Species Act in 1979 and the U.S. Endangered Species Act in 1995. At Federal listing in 1995, Indian Knob mountainbalm was known from six occurrences, two of which were in protected areas, with a total population estimate of <600 individuals. As of 2019, Indian Knob mountainbalm is known from seven occurrences, six of which are in protected areas and one (the largest) mostly in a protected area, with a total population count of 6,489+ individuals in 2016. Two occurrences are likely extirpated. Indian Knob mountainbalm is considered a fire-adapted chaparral plant. Reproduction is reported to be primarily vegetative by underground rhizomes, and it is specialized for substrates with physical disturbances, including: steep rocky slopes, cliff faces, fallen rock debris, sand dunes (shifting sand), roadsides, old graded substrates such as dirt/rock roads, the talus of graded substrates, and trails. We report the species grows up to 5.5 m tall and at 98 to 263 m elevation. In consideration of the life history traits used by Anacker et al. (2013) for rare plants in California, Indian Knob mountainbalm would be considered highly vulnerable to climate change. Using the international standards of IUCN, Indian Knob mountainbalm meets the criteria for classification as endangered including the following: geographic range, fragmented; extent of occurrence, 34 km2 (<100 km2); area of occupancy, <2.3 km2 (<10 km2); and quality of habitat, continuing to decline (dense vegetation, lack of recent fire). Coordinated conservation and research are needed to further understand the species, and to restore and maintain the five extant occurrences.