Arctostaphylos hookeri ssp. ravenii (Flowering Plants)

Species Description

Is there anything lonelier than the Presidio or Raven’s Manzanita? This evergreen shrub, a member of the heath family, is the most imperiled species in the GGNP. Indeed, one would be hard pressed to find anything more imperiled: there is only one individual plant left in the world. This last individual is currently over a century old, and to date it has not self-pollenized to create viable offspring: it is probable that this lone plant represents the last individual that will ever be known of its species. While genetically identical clones have been established, there has never been a report of natural seedling establishment by the species since it was rediscovered in 1952.

Discovered and named after the great botanist and San Francisco native Peter Raven, the Presidio Manzanita grows close to the ground in a single, coastal location characterized by serpentine soils. Because of the low calcium, high magnesium, and heavy metal content of serpentine soils, few plants grow there. Those that do tend to have an extremely restricted geographic distribution, in part because they get out-competed in areas with richer soil.

However, at one time the Presidio Manzanita could be found in multiple locations throughout San Francisco. Unfortunately, almost all of the Presidio Manzanita’s habitat was destroyed by San Francisco’s urban growth, reducing the species to its present status. Populations were destroyed near the Laurel Hill Cemetery (now bounded by California, Geary, Parker, and Presidio streets), the Masonic Cemetery (now part of the University of San Francisco campus), and the Protestant Orphan Asylum at Haight and Laguna streets, near the Duboce U.S. Mint. No plants were salvaged from these areas before they were destroyed and developed. The location of the last wild individual is a guarded secret, but is known to be within the Presidio.

The Presidio Manzanita was protected as an endangered species under the federal Endangered Species Act in 1979, shortly after the Act was passed but long after the irreversible damage to the species was done. However, the Endangered Species Act is working to preserve the Presidio Manzanita in a variety of ways: a recovery plan has been created for the species, experiments are being conducted to create viable seeds, and clonal transplants are being considered.

The Endangered Species Act is also helping combat threats to the last wild individual and its habitat. Invasive, colonizing trees and plants such as blue gum and jubata grass can overtop the prostrate Presidio Manzanita, threatening the species’ continued existence. Rigorous vegetation management is required to suppress this invasion. Disease and insect infestations have also taken a toll on the last Presidio Manzanita in recent years. Working through the Endangered Species Act, land managers have been combating these threats and trying to ensure that the species survives.

Conservation Action Item

Preserve native plants:
Volunteer with San Francisco's Natural Areas Program

The tenuous status of the Presidio Manzanita makes it difficult for the general public to even see the species, let alone help it recover. However, the City of San Francisco has a bold and progressive plan that, if fully implemented, can help ensure that no other species indigenous to San Francisco will ever again suffer such a fate. It is called the San Francisco Natural Areas Program, and it plays a key role in protecting the remnant habitats and biological communities that still remain in San Francisco. Volunteer with San Francisco’s Natural Areas Program, and help preserve what remains of San Francisco’s indigenous species.

For more information about this Conservation Action Item:

San Francisco’s Natural Areas Program

Big Year Competitors have reported 0 sightings and taken 0 actions to help this species recover so far this year.

Trips

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