|Listed||June 22, 1992|
|Description||Erect shaggy-haired annual herb with white, lavender, or rose colored flowers.|
|Habitat||Coastal foredunes and coastal dunescrub communities.|
|Threats||Invasion of alien plants, proposed commercial and residential development, hikers, livestock trampling.|
The Sonoma spineflower, Chorizanthe valida, an erect spreading buckwheat that grows 3.9-11.8 in (10-30 cm) is a shaggy-haired annual herb with basal leaves 0.4-2 in (1-5 cm) that are typically wider near the tip. Flowers appear in June-August. These flowers are white, lavender, or rose colored; are 0.2-0.26 in (0.5-0.6 cm) long; and occur in dense, ball-shaped, pink clusters with green bracts below. It is very similar in appearance to Howell's spineflower, the primary distinguishing characteristic of Sonoma spine-flower being its ascending to erect growth habit and the brightly colored red and white involucres. The bright red base of the involucre's straight spines contrasts with their bright ivory tips, and the red spine bases contrast sharply with the dull-colored involucral tube.
Dispersal of seeds is facilitated by the spines, which attach the seed to passing animals. As with other Chorizanthe species, this species occurs on sandy substrate, where seedlings establish in areas that are relatively free from other competing native species. It is unknown whether the species forms a dormant seed bank.
Sonoma spineflower flowers sometime between June and August, depending on the year's weather pattern. It has a peak blooming season of only three weeks, after which it rapidly loses color and goes to seed. After about a month, the dull brown flower-head begins to disintegrate and the spiny seeds are dispersed on the ground nearby. During the blooming period, Sonoma spineflower emits a strong floral scent which attracts many insect pollinators. Honey bees, yellow-faced bumblebees, and solitary ground nesting wasps are known to forage on Sonoma spineflower flowers. An insect identified as belonging to the order Hemiptera lygaeidae also occurs on this plant. The insect closely resembles the seeds in size and color.
Sonoma spineflower occurs exclusively in the sandy soil of a coastal near Abbotts Lagoon, at an elevation of approximately 40 ft (12 m). The prairie is adjacent to a brackish lagoon, coastal swale, and coastal scrub, but Sonoma spineflower does not grow in those. Other plants associated with this species include two species of special concern, Point Reyes horkelia and large-flower linanthus. Dominant species include coyote brush and several annual grasses.
Sonoma spineflower occurs in areas of relatively mild maritime climate, characterized by fog and winter rains. The fog helps keep summer temperatures cool and winter temperatures relatively warm, and provides moisture in addition to the normal winter rains.
Sonoma spineflower is known from one population with a maximum of 30,000 individuals, near Abbotts Lagoon in Point Reyes National Seashore, between Tomales Point and Point Reyes. Historically the plant was more widespread on the peninsula, occurring near the Point Reyes Post office, then located west of Schooner Bay, as well as north of Creamery Bay in Drakes Estero. The location of Vosnesensky's original collection in 1877 was near Fort Ross. The Fort Ross site has been surveyed many times, most recently in 1987, and Sonoma spineflower has not been found. Additional historical collections of this spineflower were recorded from near Petaluma and Sebastopol in the interior portion of Sonoma County.
The only known extant population of Sonoma spineflower is in the Lunny Pasture adjacent to Abbotts Lagoon in Point Reyes National Seashore. This site, which was discovered in 1980, is on the U.S. Geological Survey's Drake's Bay quadrangle at an elevation of about 40 ft (12 m). Before then, Sonoma spineflower had been thought to be extinct from Point Reyes, with the last collection made in 1903.
The Lunny Pasture population of Sonoma spine-flower was estimated to cover 1,100 sq ft (102 sq m) in 1983. In 1984, more than 2,000 plants covered an area of 16,829 sq ft (1,471 sq m). The increase in population area from 1983 to 1984 was probably due to natural population fluctuations that occur in annual species in response to weather conditions. A 1986 survey estimated that the colony of Sonoma spine-flower in Lunny pasture consisted of two distinct subpopulations covering approximately 4.2 acres (1.7 hectares) and well more than 2,000 plants. Subsequent monitoring by the California Native Plant Society has documented wide fluctuation in numbers, ranging from 2,000 to 30,000 plants. Variation between estimates may be due to undercounting, differences in observer accuracy, or the natural fluctuations between years.
The rarity of Sonoma spineflower (one extant population) makes it exceptionally vulnerable to disturbances. Development may have led to the loss of the historical mainland populations of this species near Sebastopol and Petaluma, California, if indeed populations existed inland from Point Reyes.
The extant population is in the Point Reyes National Seashore, inside a pasture that has been grazed for over a century. The Point Reyes National Seashore issues special use permits to ranchers for dairy and beef operations because the enabling legislation for the park considers that cattle ope'rations merit preservation as part of the cultural heritage of western Matin County. Changes in grazing or trampling intensity could alter the vegetation structure that has allowed Sonoma spineflower to persist. Increased grazing or trampling may increase seedling mortality, and reduced grazing/trampling could allow surrounding vegetation to close vegetation gaps and outcompete Sonoma spineflower.
Conservation and Recovery
Point Reyes National Seashore performs yearly monitoring of Sonoma spineflower and other rare species. Volunteers from The California Native Plant Society monitor the rare plant populations at Point Reyes National Seashore, but not yet on an annual basis.
The possibility that grazing may benefit Sonoma spineflower by suppressing competitors has been investigated. Exclosures were built in 1988 and the colony was monitored. A higher density of Sonoma spineflower was found outside the exclosures than inside, and it was suggested that this species may be adapted to a grazing regime. However, the plants inside the exclosures were more than twice as tall as the plants outside, growing as tall as the grasses that were protected from cattle. There were no plants inside the exclosures in 1996. A change in the grazing regime may allow for an increase in both the number and size of the plants.
In 1988 seeds were collected and introduced into three 10 by 10 ft (3 by 3 m) plots within 600 ft (183 m) of the existing occupied site. The sites had successful reproduction and two expanded outside the original seeded area. The successful introduction of species into appropriate habitat is important for this species' long term survival.
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
Sacramento Ecological Services
Field Office Room E-1803/1823
2800 Cottage Way
Sacramento, California 98525
Telephone: (916) 978-4866
Fax: (916) 978-4613
U.S. Fish and Wildlife Service. 22 June 1992. "Endangered and Threatened Wildlife and Plants; Six Plants and Myrtle's Silverspot Butterfly From Coastal Dunes in Northern and Central California Determined to be Endangered." Federal Register 57 (120): 27848-27858.