Indian Knob mountainbalm (Eriodictyon altissimum) is a state and federally listed evergreen shrub in the family Namaceae.. This long-lived plant is endemic to California, occurring only in western San Luis Obispo County. The species can reach up to 18 feet in height and has lavender bell-shaped flowers. As of 2019, there are seven known occurrences. Two of these occurrences are likely extirpated (locally extinct), and five occurrences are extant (still existing). The entire geographic range for this species is approximately 13 square miles. Indian Knob mountainbalm occurs in coastal chaparral and is considered a fire-adapted species. It is highly vulnerable to and is experiencing decreasing habitat quality due to progressively dense vegetation and altered fire regimes. Little is known about the biology and ecology of this species. Research and management are needed to restore and maintain the five extant occurrences.
Indian Knob mountainbalm is a tall evergreen shrub that can reach up to 18 feet in height and up to 7.9 inches in basal stem diameter; however, most individuals are smaller. It is diffusely branched with long, narrow leaves and bell-shaped flowers. Individuals only several inches tall can produce flowers. This species will initially grow vertically; however, due to its pliable stems and branches, as the species grows taller, it will begin to bend unless otherwise supported by adjacent vegetation. As a result, sometimes this species will have stems or branches laying horizontally on the ground.
This species has long, narrow green leaves. The flowers are bell-shaped and lavender in color.
Little is known about the reproduction and life cycle of Indian Knob mountainbalm. However, assumptions can be made based on the closely related species of the genus Eriodictyon. The species is assumed to be a fire-adapted species; however, no direct evidence for this exists as there hasn't been a recent fire in any of the known occurrences. California yerba santa (Eriodictyon californicum), a closely related species, is a fire-following species, which means that seeds will be stored in the soil for decades and germinate in the first spring after a fire. Indian Knob mountainbalm is expected to be similar. While the role fire plays in its reproduction is uncertain, fire clears dense vegetation and Indian Knob mountainbalm may use fire as a cue to begin seed germination and seed production.
It is thought that this species reproduces primarily via asexual vegetative reproduction, meaning that underground shoots called rhizomes spread horizontally and send up new vertical stems. Due to this method of reproduction, some occurrences may have low genetic diversity and could consist of a single clonal individual. New stems are produced from these underground rhizomes when the aboveground stems are removed or disturbed. This species can also reproduce via seeds but is expected to be self-incompatible, meaning fertilization is needed from another genetically distinct plant. Floral visitors and potential pollinators include insects such as ants, beetles, bumblebees, flies and butterflies.
It is assumed that this species has a long lifespan due to slow-growing lichen found on some individuals, and it seems some individuals may even reach more than 50 years of age.
Indian Knob mountainbalm occurs within coastal chaparral plant communities. Coastal chaparral is characterized by the presence of native species such as manzanita. Indian Knob mountainbalm is considered to be a pioneer species. Pioneer species are the first to grow in a newly disturbed environment. As such, this species is found in sand dunes, trails, roadsides, cliff faces and rocky slopes, all environments subject to physical disturbances. This species occurs at elevations between 322 and 863 feet and exists in the Mediterranean climate area (warm dry summers, cool wet winters) of coastal San Luis Obispo County.
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