Tiburon Jewelflower

Streptanthus niger

Description

The Tiburon jewelflower, Streptanthus niger, is an annual herb of the mustard family (Brassicaceae or Cruciferae) that reaches 1-2 ft (30.5-61.0 cm) in height. The lower leaves are toothed, the upper leaves less toothed or not at all. The sepals are a very dark purple; the petals have a purple claw and a white blade with a purple midvein. The pods are erect, almost straight and 1.5-2.75 in (3.8-7.0 cm) long. The zig-zag inflorescence pattern and the lack of hairs distinguish S. niger from its near relative S. glandulosus. Seedlings of Tiburon jewelflower appear in March and April, and the plants flower from May to June. The species is self-pollinated. The seed capsules open in late June.

Habitat

Tiburon jewelflower is found on shallow rocky serpentine soils on slopes of the southern Tiburon Peninsula at elevations of approximately 350 ft (107 m). Associated federally listed species are Matin dwarf-flax and Tiburon paintbrush.

Distribution

Tiburon jewelflower is found on the Tiburon Peninsula of Matin County. Two populations are known from the southern end of the peninsula where they occur within 2 mi (3.2 km) of one another. One is at the tip of the peninsula near St. Hilary's Church, and the other is along the Middle Ridge of the peninsula. The species probably never occurred outside of the Tiburon Peninsula, and no historic populations are known.

Populations have fluctuated from 50 to 2,000 plants. A 1990 survey found a total of approximately 800 plants in the two populations together. The known populations combined comprise approximately 12 acres (4.9 hectares) of habitat.

Threats

Tiburon jewelflower is an extremely narrowly-distributed species; its entire range amounts to less than one-third of a square mile. Urban development has destroyed over 40% of potential Tiburon jewelflower habitat.

One parcel, containing approximately 65% of all plants of this species, was the proposed site for 30 homes. Although this project did not propose to directly eliminate the plants, impacts from potentially harmful runoff from upslope construction and landscaping, accelerated erosion, introduction of weedy species during construction, alteration of hydrology, and uncontrolled foot traffic would have threatened the plants. The proposed development was denied by the Town of Tiburon. An area containing 20 plants adjacent to this parcel was bull-dozed for construction of condominiums. Residential development is ongoing at several parcels of the Middle Ridge population.

In addition to urbanization, pedestrian traffic, dog walking, invasion of non-natives and road construction threaten the Tiburon jewelflower populations. Invasive non-natives, such as french broom, that have been removed by volunteers in the past, have reinvaded. Further, because there are only two populations of Tiburon jewelflower which occur in close proximity to each other, the species may be at risk of extinction from random events or from natural catastrophes.

Conservation and Recovery

Recovery of Tiburon jewelflower must first focus on protecting and managing the two natural populations by working with the Town of Tiburon, Matin Open Space District, Tiburon Landmark Society and other landowners.

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
(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.