Presidio Clarkia

Clarkia franciscana

Description

Presidio clarkia (Clarkia franciscana ) is a slender, erect, herbaceous annual of the evening-primrose family (Onagraceae). It reaches a height of 16 in (40.6 cm) and has few, very small, narrow leaves. The lavender-pink petals have a lighter basal portion and a reddish-purple basal spot. The slender capsule is 1-2 in (2.5-5.1 cm) long. Presidio clarkia can be distinguished from C. rubicunda, a related species that may occur in the same area, by its petals, which have irregular teeth on the apical margin. C. rubicunda has petals that are rounded at the apex and usually twice the length of those on Presidio clarkia.

Presidio clarkia flowers from May to July. At the Presidio in California's San Francisco County, it is visited by small sweat bees, which may be pollinators of the species. However, plants can self-pollinate by shedding pollen directly on the stigma (female reproductive part), and the species is thought to be predominantly self-pollinated in natural populations.

Habitat

Presidio clarkia is the only species of Clarkia restricted to serpentine soils. Known locations span elevations of approximately 75-1,100 ft (23-335 m). Other rare species occurring with Presidio clarkia include the federally endangered Presidio manzanita and most beautiful jewelflower, a species of concern.

Distribution

Presidio clarkia was once thought to be restricted to the Presidio in San Francisco County, but in the mid-1980s a population was discovered in Alameda County in the Oakland Hills. Two populations are known from the Presidio in San Francisco; one of these is probably introduced. A third population at the Presidio is probably extirpated.

Three populations are known from the Oakland Hills, 17 mi (27.4 km) east of San Francisco, all within 0.6 mi (1 km) of each other. These have been called the Crestmont, Old Redwood, and Redwood Park sites and are probably the remaining portions of one population that has been fragmented by roads and houses.

A fourth population in the Oakland Hills was reported in 1988 but could not be relocated during a search conducted in 1991.

Population sizes fluctuate greatly for reasons that are not understood. The upper limit to the total numbers of plants reported at the end of the twentieth century was approximately 8,000.

Threats

Presidio clarkia is threatened by potential development, roadside maintenance, foot traffic, mowing, competition from non-native plants, and shade from native and introduced shrubs and trees. The Presidio populations are threatened by habitat degradation, including mowing, trampling, roadside maintenance, and presence of non-native species. The Presidio represents a significant natural and cultural resource within San Francisco city limits and was expected to be widely promoted and heavily used by visitors after transfer to the National Park Service. Increasingly heavy use by visitors could increase negative impacts on Presidio clarkia. Road maintenance and mowing of grasslands before Presidio clarkia has set seed also threatens the Presidio populations, as does the encroachment of non-native plant species, including German ivy, iceplant, blackberries, non-native grasses, and natives planted outside their natural range (such as Monterey pine).

Two years of sampling indicate that serpentine grasslands at the Presidio support nearly 50% cover of non-native grasses, particularly soft brome and Italian ryegrass. The population size at the type locality increased following removal of non-native plant species in 1988. Removal of Monterey pines in 1995 also allowed Presidio clarkia to move into previously unoccupied habitat.

The three populations of Presidio clarkia in Alameda County are all threatened by non-native species. The smallest of the three at Crestmont, consisting of 30 plants, occurs on an undeveloped site adjacent to a proposed 32-unit residential development and may be affected by collection, trampling, and other human disturbances if the site becomes developed.

At latest report, the largest population of Presidio clarkia, occurring at Redwood Regional Park in Alameda County, consisted of 4,000-5,000 plants. Previous threats to the largest segment of this population, below the former East Bay Regional Parks District headquarters, included proposed expansions of the headquarters, improvements to adjacent equestrian facilities, and invasive non-native species. Most of these threats have apparently been removed. (For example, the equestrian facility has been relocated.) The East Bay Regional Parks District is aware of the Presidio clarkia population and has been taking it into account in their management plans. The habitat is still threatened by competition with annual grasses and other non-native plants, including pampas grass and french broom. The portion of this population that occurs off of East Bay Regional Parks District land is threatened by proposed developments, herbicide applications, and invasive non-native plants such as pampas grass.

The two smaller populations in Alameda County, consisting of 200 plants (Old Redwood) and 30 plants (Crestmont) respectively, are also threatened by non-native species such as french broom and pampas grass. The larger of these populations is isolated and on a roadcut and may be threatened by roadside spraying of herbicides for weed control. The other population site is being rapidly displaced by non-native vegetation and is for sale. In addition, low viability caused by harmful genetic changes may result from inbreeding in small populations.

Conservation and Recovery

Presidio populations of Presidio clarkia have been monitored annually since 1994. The largest population at the Presidio was fenced in 1995, and invasive Monterey pines occupying serpentine soil were removed in 1995-96. Following tree removal in 1995, Presidio clarkia moved into the newly open habitat. Efforts to improve habitat by clearing non-natives and removing accumulated acidic soils are ongoing at the Presidio. East Bay Regional Parks District has also taken some measures to control non-native invasive species, including removal of Monterey pines, pampas grass, french broom, and acacias. Using prescribed fire is also a possibility to control undesirable vegetation and promote growth of native species. Seeds of Presidio clarkia are stored at the University of California Botanical Garden as part of the Center for Plant Conservation's National Collection of Endangered Plants, and the species is apparently easy to grow. As of 1993, the East Bay Regional Parks Botanic Garden had an extensive growing collection of Presidio clarkia.

Contact

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

Reference

U. S. Fish and Wildlife Service. 1998. "Recovery Plan for Serpentine Soil Species of the San Francisco Bay Area." Portland, Oregon. 330+ pp.