Arctostaphylos hookeri var. ravenii
|Listed||October 26, 1979|
|Description||Low-growing, spreading shrub with elliptical, shiny leaves and white flowers.|
|Habitat||Acidic serpentine soils in direct sunlight.|
|Threats||Low numbers, limited distribution.|
Presidio manzanita, Arctostaphylos hookeri var. ravenii, or Raven's manzanita, is a low, spreading shrub, reaching 1 ft (30 cm) in height and up to 8 ft (2.4 m) in diameter. Shiny green leaves are elliptical. White flowers tinged with pink bloom March to April. The fruit is a bright red berry. Like other manzanitas, fruits and flowers are often concealed under foliage. The species self-pollinates both in the wild and in cultivation. Seedlings have not been observed in the wild.
Presidio manzanita grows best on slightly acidic, serpentine soils that occur in isolated outcrops. Serpentine soils are high in magnesium and low in calcium, a combination that is inhospitable to many common plants. Serpentine plants tend to grow with little competition and are poor competitors on other soils. Manzanita thrives in direct sunlight and is shade intolerant. Fire is believed crucial for helping to break the dormancy of seeds and for preparing an appropriate seed bed.
Presidio manzanita is endemic to the serpentine outcrops of the San Francisco Bay region. Known historic localities were grouped within a five mile radius. Specimens were present at the Laurel Hill Cemetery and nearby Masonic Cemetery in the 1940s but were lost to urbanization. Plants, surveyed on the summit of Mount Davidson in the 1950s, were bulldozed to erect a large cross. Presidio manzanita also populated a site at the Protestant Orphanage—now part of the University of California Extension Center.
When listed in 1979, a single plant survived in the wild on a west-facing slope, 270 ft (90 m) above the Pacific Ocean, on the Presidio Army Base. This site in San Francisco County is now managed by the U. S. Fish and Wildlife Service (FWS). Other plants of this population were eliminated by wartime construction of gun emplacements. The plant has since been zealously maintained by base commanders. Should the Army dispose of the base, the site would be added to the Golden Gate National Recreation Area.
Conservation and Recovery
Recovery efforts have focused on the captive propagation of plants and their reintroduction. The FWS Sacramento Office, the California Department of Fish and Game, the National Park Service, Presidio of San Francisco, Berkeley Botanical Garden, East Bay Regional Parks Botanic Garden, and Saratoga Horticultural Foundation have all collaborated in the effort.
Events in 1987 were encouraging for the recovery of Presidio manzanita. Twenty-two cuttings from the surviving plant were reintroduced into the Golden Gate National Recreation Area. As of June 1989, 14 of these plants survived and appeared to be thriving. Fifty cuttings were transplanted on Army land at Presidio, and about half of these have survived. The Berkeley Botanical Garden germinated and grew new plants from the seed of the wild plant—the first time this has been successful.
Eighteen cuttings were set out on Presidio land in December 1988 and survived as of April 1989. These cuttings were all about 3 in (8 cm) high, growing from a single shoot. Botanists will continue to transplant cuttings from nursery-grown plants.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Hans, T. L. 1977. "California Chaparral." In M. G.Barbour and J. Major, eds., Terrestrial Vegetation of California. Wiley, New York.
Kruckeberg, A R. 1977. " Arctostaphylos Hybrids in the Pacific Northwest." Systematic Botany 2: 233-250.
Ornduff, R. 1974. An Introduction to California Plant Life. University of California Press, Berkeley.
Roof, J. B. 1980. "A Fresh Approach to the Genus Arctostaphylos in California." Changing Seasons 1(2): 2-32.
U. S. Fish and Wildlife Service. 1984. Recovery for the Raven's Manzanita. U. S. Fish and Wildlife Service, Portland.