Indian Knob Mountainbalm

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Indian Knob Mountainbalm

Eriodictyon altissimum

ListedDecember 15, 1994
FamilyHydrophyllaceae (Waterleaf)
DescriptionDiffusely branched evergreen shrub; bears lavender flowers.
HabitatSoils derived from marine sandstones containing tar deposits; in the northernpart of its range, on Baywood fine sands and weathered ancient dune soils.
ThreatsPotential for development.


Indian Knob mountainbalm, Eriodictyon altissimum, is a diffusely branched evergreen shrub of the reaches a height of 6.6-13 ft (2-4 m). The sticky leaves are long, 2.4-3.5 in (6.1-9 cm), and narrow, ranging from 0.08-0.20 in (0.2-0.5 cm) wide; the lavender flowers are arranged in coiled clusters and produce tiny seeds. As with other fire-adapted chaparral plants, Indian Knob mountainbalm produces new growth primarily from rhizomatous suckers. Only two other narrow-leaved Eriodictyon species occur in southern California; narrow-leaved yerba santa (E. angustifolium ) occurs in the New York Mountains in the eastern Mojave Desert and has much smaller flowers. The other, Lompoc yerba santa (E. capitatum ), is restricted to a few locations in coastal Santa Barbara County and has a distinctly capitate (headlike) inflorescence.

This perennial shrub is believed to be relatively long-lived; slow-growing lichens can be found attached to its woody stems. Indian Knob mountain-balm flowers in June and July. A variety of nonspecialist potentially pollinating insects have been recorded visiting the flowers of this species. Fruits contain a single ovule and seed set is low in those plants in which it has been recorded. A related species, Lompoc yerba santa, is self-incompatible and reproductive and genetic studies suggest that small colonies may consist of only a single genotype (clone). It is not known if Indian Knob mountainbalm is self-compatible; however, it is possible that some colonies are also composed of a single clone. In addition to sexual reproduction, this species regenerates by root sprouts.


Indian Knob mountainbalm occurs in soils derived from marine sandstones containing tar deposits referred to as "tar sands" and, in the northern part of its range, on Baywood fine sands and weathered ancient dune soils. This species co-occurs with Morro manzanita in several locations in maritime chaparral.

As with other members of this genus, Indian Knob mountainbalm is thought to be adapted to ecologic disturbance, specifically to periodic fire within the chaparral community. Field botanists have noted that most stands of Indian Knob mountainbalm are mature or senescent, and that prescribed fire may be needed to revitalize the stands.


Only six stands of Indian Knob mountainbalm are known. Five of six extant stands occur within a few square miles of each other, from the south side of the community of Los Osos to the north end of Montafia de Oro State Park. Each of these stands has fewer than 50 plants. A sixth stand is found 15 mi (24 km) to the southeast on Indian Knob, between San Luis Obispo and Arroyo Grande; with more than 500 plants, it comprises the largest stand. Estimates of population sizes are imprecise because Indian Knob mountainbalm sprouts from the root, making identification of a genetic or physiological individual difficult. Two of the Morro Bay stands are on lands owned and managed by Montafia de Oro State Park, and co-occur with Morro manzanita in Hazard Canyon. The remaining stands are on private property. Because rugged terrain in the Irish Hills, between Morro Bay and Indian Knob, has precluded extensive botanical surveying, it is not known whether other stands of Indian Knob mountainbalm occur in this area.


The potential for development is the greatest threat to Indian Knob mountainbalm on private lands. In the early 1990s, a water storage tank was installed within 100 ft (30.5 m) of one occurrence north of Highland Drive on private property. Surface mining of tar sands was proposed several years ago for the Indian Knob area; however, part of this stand now receives protection through a conservation easement that restricts mining activities. At Montafia de Oro State Park, a communications line installed in Hazard Canyon in the early 1990s would have affected scattered individuals, but efforts were made to avoid them.

Conservation and Recovery

This species was listed by the State of California Fish and Game Commission as endangered in 1979. The City of San Luis Obispo has purchased a conservation easement that provides protection to a large portion of the known population at Indian Knob. The easement covers almost 1500 acres (607.1 hectares) and restricts mining and development where the known population of the mountainbalm occurs.


U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121


U.S. Fish and Wildlife Service. 1998. "Recovery Plan for Morro Shoulderband Snail and Four Plants from Western San Luis Obispo County, California." U.S. Fish and Wildlife Service, Portland, Oregon. 75 pp.