Tiburon Paintbrush

Castilleja affinis ssp. neglecta

Description

Tiburon paintbrush, Castilleja affinis ssp. neglecta, is a semi-woody perennial of the snapdragon family (Scrophulariaceae), with erect, branched stems 1-2 ft (30.5-61 cm) tall and a sparse covering of soft, spreading hairs. The lance-shaped leaves are 0.8-1.6 in (2-4 cm) long and have zero to five lobes. The conspicuous floral bracts are yellowish and sometimes red-tipped; the flowers are yellow to red and 0.7-0.8 in (1.8-2 cm) long. The simple hairs and the lack of glands below the inflorescence distinguishC. affinis ssp. neglecta from other species of Castilleja on the Tiburon Peninsula.

Tiburon paintbrush is a perennial, flowering from April to June. Its yellow flowers are largely bee-pollinated. Seeds are shed in June and July, and the species dies back to its woody base in July and August. New growth from the woody base begins in December or January. Seeds may remain dormant in the soil for several years. Seed germination occurs in January or February and seems to be induced by leaching and low temperatures.

Most plants have three or fewer inflorescences with about eight seed capsules per inflorescence containing about 1,600 seeds per plant. In the laboratory, Tiburon paintbrush seedlings survived over a wide range of calcium/magnesium ratios. However, factors such as local climate, soil, and herbivory may profoundly influence germination rate, seedling establishment, and survivorship in nature.

Tiburon paintbrush is a root parasite on other angiosperm species. The primary advantage of the parasitic attachment in Castilleja and related plants in the figwort family is reportedly an increased water and mineral supply. Though the parasitic relationship is not obligatory, benefits to species of Castilleja from the parasitic habit are manifested in increased vigor with more branching, greater height, and earlier flowering. The host plant increases Tiburon paintbrush's chance for survival. Experiments and field data suggest that Tiburon paintbrush species may utilize a variety of host species.

Habitat

Tiburon paintbrush occurs in serpentine bunch-grass communities at elevations between about 250-1,300 ft (76-396 m), where it occurs in areas typical of serpentine soils in general. In one study, calcium/magnesium ratios at the American Canyon site were higher than those at the sampled Tiburon sites. Tiburon paintbrush occurs in close proximity to Santa Clara Valley dudleya in Santa Clara County. Other associated rare species include Marin dwarf-flax, serpentine reedgrass, Tiburon buckwheat, and Tiburon jewelflower. Other native plants occurring at sites with Tiburon paintbrush include California gilia, California melic, California poppy, dwarf plantain, foothill needlegrass, hayfield tarweed, longhorn plectritis, purple needlegrass, purple sanicle, royal larkspur, slender fairyfan, stickywilly, and Torrey's melicgrass. Associated introduced species include Italian rye-grass, slender wild oat, and soft brome.

Distribution

Tiburon paintbrush has never been widespread. Three of the seven known populations occur on the Tiburon Peninsula in Marin County, one occurs in Napa County, and one in Santa Clara County. Recently discovered populations on Golden Gate National Recreation Area and east of Anderson Lake extend the known range to western Marin and Santa Clara Counties, respectively. Tiburon paintbrush is known from five populations in Marin County, three of which occur on the Tiburon Peninsula, from one population in American Canyon in Napa County, and from one population in Santa Clara County. The range of this plant is approximately 30 mi (48.3 km) from east to west, and 70 mi (112.6 km) from north to south. Population sizes are small, ranging from less than 20 plants at the Santa Clara County site to approximately 600 plants at Ring Mountain Preserve on the Tiburon Peninsula.

Threats

Populations of Tiburon paintbrush occur on public and private land in Marin County, and exclusively on private land in Napa and Santa Clara Counties. The Marin County populations are threatened by residential development, foot traffic, grazing, and soil slumping. Each of the three populations on the Tiburon Peninsula has multiple landowners. Marin Open Space District owns over half of the Ring Mountain population formerly owned by the Nature Conservancy, and the town of Tiburon owns portions of the population in the Middle Ridge area of the peninsula. The remainder of each of these populations is privately owned. The third population on the peninsula is in the vicinity of St. Hilary's Church in Tiburon.

Development on the Tiburon Peninsula has been extensive and rapid; more than 60% of Tiburon paintbrush habitat has already been destroyed by development. Residential development begun in the early 1980s is ongoing in the vicinity of the Middle Ridge population. A portion of the Middle Ridge population was extirpated by development about 1990. The town of Tiburon is currently considering a proposed development (Easton Point) that could impact the species as well as Marin dwarf-flax in the vicinity of St. Hilary's Church. A second proposed development in the same area was denied by the town of Tiburon. The area that would have been involved in this second development has been set aside as open space.

The southernmost population of Tiburon paint-brush on the Tiburon Peninsula, in the vicinity of St. Hilary's Church, is probably located within this proposed open space. The habitat in the area is also threatened by pedestrian traffic and by invasion of non-natives such as pampas grass, broom, and blackberry. A subpopulation on Middle Ridge is also threatened by invasion of pampas grass. The plants on Ring Mountain Preserve are protected from development but are threatened by sliding of the slope on which they occur. The toe of the slope was removed to accommodate residential development in the 1960s. Soil material that slides into the street at the base of the slope is removed by the City of Corte Madera, and the slope continues to slump. Managers from the Nature Conservancy estimate that approximately one-third of the population is at risk. The western Marin populations at Golden Gate National Recreation Area are located in areas that are being grazed by cattle; the impact of the grazing needs to be determined.

The Napa County population is threatened by gravel mining and grazing. The Napa County population occurs on private property near a gravel quarry. The property is used by Syar Industries for the mining of road base materials. The long-term effect of ambient dust from mining has the potential to alter soil chemistry and photosynthesis. Although quarry expansion plans that would result in the destruction of more than 80% of the population are no longer actively being pursued, the potential for expansion still exists. Cattle grazing also has been reported to threaten a portion of the American Canyon population. The Santa Clara County population consists of 13 plants that may also be subject to grazing.

Conservation and Recovery

Between 1982 and 1995, over half of the Ring Mountain population of Tiburon paintbrush was protected from development because the land on which it occurs was owned and managed by the Nature Conservancy, a group whose management goals are the maintenance of biodiversity and the protection of rare and endangered species. The Ring Mountain property was transferred to Marin County Parks and Open Space in 1995. The Nature Conservancy retained a conservation easement on the property and expects that Marin County will continue monitoring the rare species on the preserve. At this point, the county is depending on volunteers from the Nature Conservancy and the California Native Plant Society for monitoring. The preserve is fenced to reduce the incidence of four-wheel drive vehicle and motorcycle use, but is still accessible to bicycles, equestrians, and hikers. In addition, two populations of Tiburon paintbrush are on Golden Gate National Recreation Area land that is managed by Point Reyes National Seashore. The effect of cattle grazing on these populations is unknown, but at least one population is monitored by the California Native Plant Society. The Santa Clara County population of Tiburon paintbrush is on a reserve for bay checkerspot butterfly conservation.

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.