|Listed||February 3, 1995|
|Description||Small annual plant, has one or a few branches, bears white to purplish ray flowers.|
|Threats||Urbanization, recreational development, non-native plant species.|
White-rayed pentachaeta, Pentachaeta bellidiflora, is a small annual plant of the aster family (Asteraceae) with one or a few branches that bear narrow, linear leaves. Each flower head has numerous yellow disk florets in the center portion of the head, and five to 16 white to purplish ray flowers. The fruits are tawny, coarse-haired achenes (dry one-seeded fruits). Related species in the San Francisco Bay area, P. exilis ssp. exilis, meager pentachaeta and P. alsinoides, tiny pentachaeta, differ from P. bellidi-flora in that they have no ray flowers.
White-rayed pentachaeta flowers from March to May and may be visited by the federally threatened bay checkerspot butterfly. The butterfly may incidentally pollinate the plant, but the primary pollinators of white-rayed pentachaeta are unknown. Given that the seeds apparently do not overwinter well, the species may have a limited soil seed bank.
White-rayed pentachaeta grew in serpentine grassland between 120 and 2,000 ft (36 and 600 m). The one remaining location is found at approxi-mately 520 ft (156 m) with dwarf plantain, purple needlegrass, and tidy-tips. Rare species in the area include the federally threatened bay checkerspot butterfly and Marin dwarf-flax and the federally endangered fountain thistle and San Mateo thornmint. Although in the vicinity, Marin dwarf-flax is not directly associated with white-rayed pentachaeta.
Historically, white-rayed pentachaeta was known from at least nine sites in Matin, San Mateo, and Santa Cruz Counties. Most populations were destroyed by urbanization, off-road vehicles, or highway construction over the second half of the twentieth century. Suitable habitat remains in two San Mateo County locations, but the species has not been seen at either site in many years. White-rayed pentachaeta is now known from only one confirmed location in San Mateo County, in the "Triangle" area and adjacent Edgewood County Park. A second population may have been found on the west side of Crystal Springs Reservoir on San Francisco Water Department land, but the sighting needs to be confirmed.
As is common among annual plants, white-rayed pentachaeta population size fluctuates dramatically from year to year. Numbers have ranged from 10,000 to just under 100 million in the last 10 years, with about 1.5 million plants growing in 1991 and 1992.
White-rayed pentachaeta historically ranged from Marin County to Santa Cruz County. Three populations in Marin County and two in San Mateo County were destroyed by urbanization. One Marin County population was destroyed by off-road vehicles. Two sites in Santa Cruz County no longer support white-rayed pentachaeta.
The single remaining population of white-rayed pentachaeta was bisected by the construction of California Interstate 280 in the late 1960s. The largest portion of the population occurs in the Triangle, on land administered by the San Francisco Water Department. A small remnant of this population is located to the east of Interstate 280, on Edgewood County Park. In the Triangle/Edgewood location the species is threatened by recreational development. Although public access was restricted in the past, the Triangle portion of the population is now part of a recreational easement. The proposed construction of trails on San Francisco Water Department land in the Triangle threatens white-rayed pentachaeta habitat. The Edgewood Park portion of the population is on land owned by San Mateo County. The park has been designated a natural preserve. San Mateo County is currently working on a Master Plan for Edgewood. It is possible that some disturbance could result from changes implemented as a result of the plan, but no decisions about specific actions have been made at this time, and San Mateo County personnel are aware of the population.
White-rayed pentachaeta potentially is also threatened by competition from non-native plant species; competition becomes a problem when the soils are disturbed. If proposed trail construction occurs on the site, the soil disturbance could result in encroachment and competition from non-native species. In addition, the existence of the species in only one location makes it vulnerable to extinction due to catastrophic events.
Conservation and Recovery
The only remaining population occurs in the Triangle and Edgewood Park. San Mateo County manages Edgewood as a natural preserve and has adopted a master plan to guide future activities in the park. San Mateo County personnel are aware of the special status plant species at Edgewood.
U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Avenue
Portland, Oregon 97232-4181
Telephone: (503) 231-6118
Fax: (503) 231-2122
U.S. Fish and Wildlife Service. 1998. "Recovery Plan for Serpentine Soil Species of the San Francisco Bay Area." Portland, Oregon.