San Diego Thornmint

Acanthomintha ilicifolia

Description

The San Diego thornmint is an annual herb of the mint family (Lamiaceae), with an aromatic scent. It has paired, oppositely arranged leaves, and its flowers are arranged in whorls with sharply spined bracts (modified leaves) below. The San Diego thornmint can be distinguished from other species in the genus Acanthomintha by the hairless anthers and style of its flowers. The corollas (fused petals) are tubular, two-lipped, and white with rose markings on the lower lip.

Habitat

The San Diego thornmint occurs in openings within coastal sage scrub, chaparral, and native grassland. It occurs in sites with heavy, clay, gabbro soil derived from igneous rock or from calcareous marine sediments.

Distribution

The San Diego thornmint occurs in isolated populations in coastal San Diego County and south to San Telmo in northern Baja California, Mexico.

Threats

The most important historical and ongoing threat to the San Diego thornmint is the conversion of its natural habitat to urban and agricultural land-uses. This is a threat both in San Diego County and in Baja California. Additional threats include disturbances by off-road vehicles, trampling by cattle and humans, and invasion of the habitat by non-native plants. About 40% of the 52 historically known populations of the rare thornmint in the United States have been extirpated. The 32 surviving U. S. populations support about 150,000-170,000 individuals. The rare thornmint only occupies about 400 acres (156 hectares). About 60% of the U. S. population occurs in four populations (Sycamore Canyon, Slaughterhouse Canyon, and two sites on Viejas Mountain). Eleven of the 32 surviving populations support more than 3,000 individuals each. At least nine sites are known to have recently supported the San Diego thornmint in Baja California, but the recent status of this plant in Mexico is not known.

Conservation and Recovery

There are nine U. S. populations of the San Diego thornmint containing more than 3,000 individuals. Four of these relatively large populations are located within the Multiple Species Conservation Program (MSCP) planning subregion of southern San Diego County. Two of them, located at Sabre Springs (private ownership) and Sycamore/Slaughterhouse Canyons (San Diego County ownership) are being properly conserved by the MSCP. Another population, owned by a private company, is in the MSCP outside of the Multiple Habitat Preserve Area (MHPA), but will receive significant conservation benefits within the Metro-Lakeside-Jamul segment of the MSCP of the County of San Diego. The last of these four populations, Otay Lakes Northeast (private ownership), is not adequately protected. The other seven major populations (containing over 3,000 individuals) are located either north or east of the MSCP subregion. Of these seven major populations, four are located within lands managed by the Forest Service (on Viejas and Poser mountains). The three remaining major populations and the majority of the smaller populations are on lands managed by private owners. Conservation of the San Diego thornmint requires that more of the critical habitats of its larger populations be designated as ecological reserves. This can be done by designating land already owned by a government agency, by acquiring private land, or by negotiating conservation easements. Research into the biology and ecological needs of the endangered plant is also needed in order to develop effective ways of managing and conserving its habitat.

Contacts

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
http://pacific.fws.gov/

U. S. Fish and Wildlife Service
Carlsbad Field Office
2730 Loker Avenue West
Carlsbad, California 92008-6603
Telephone: (760) 431-9440
Fax: (760) 431-9624

References

Reiser, Craig.1994. "San Diego Thorn Mint [Acanthomintha ilicifolia (Gray) Gray]." Rare Plants of San Diego County. (http://www.sierraclub.org/chapters/sandiego/rareplants/003.html). Date Accessed: July 6, 2000.

U. S. Fish and Wildlife Service. 13 October 1998. "Endangered and Threatened Wildlife and Plants: Determination of Endangered or Threatened Status for Four Plants From Southwestern California and Baja California, Mexico." Federal Register 63 (197):54937-54956.