Vine Hill Clarkia

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Vine Hill Clarkia

Clarkia imbricata

ListedOctober 22, 1997
FamilyOnagraceae (Evening Primrose)
DescriptionAn erect, annual, herbaceous wildflower with lavender fan-shaped petals.
HabitatSandy, temperate grasslands.
ThreatsHabitat destruction by conversion to agriculture or residential land-use, mowing for fire control, and collecting.


F. Harlan Lewis and Margaret Lewis described Clarkia imbricata (Vine Hill clarkia) in 1953 from specimens they collected on July 10, 1951, along Vine Hill Road in Sonoma County. This treatment continues to be accepted.

Clarkia imbricata is an erect, annual herb in the evening-primrose family (Onagraceae). The stems grow to 2.5 ft (0.7 m) tall, unbranched or with numerous short branches in the upper parts. This plant is densely leafy, with entire and lanceolate leaves 0.8-1.0 in (20-25 mm) long and 0.2-0.3 in (4-7 mm) broad that are ascending and overlapping. The showy inflorescences appear from June through July. The flowers are grouped closely together and each flower has a conspicuous funnel-shaped tube at its base. Each flower has four fan-shaped, lavender petals 0.8-1.0 in (20-25 mm) long with a V-shaped purple spot extending from the middle to the upper margin of the petal. Clarkia purpurea ssp. viminea is the only other Clarkia taxon with which C. imbricata can be confused. C. purpurea ssp. viminea has a much shorter, funnel-shaped tube and does not have the relatively broad, ascending, overlapping leaves of C. imbricata.


The Vine Hill Clarkia grows in sandy, temperate grasslands in a Mediterranean climatic regime.


C. imbricata has never been known to be common, and unsuccessful searches for this plant at its type locality have been made since 1974. This taxon is only known from one natural population and one population planted in a preserve, both found in sandy grasslands in Sonoma County. The natural population was the source for cuttings that were transplanted into the 1.5 acres (0.6 hectares) preserve in 1974. The two populations are 0.75 mi (1.2 km) apart, have an elevation range of 200-250 ft (60-75 m), and occur on private land. The natural population contains 2,000-5,000 plants and occurs on an open, flat grassland surrounded by a variety of introduced trees and shrubs. The planted population, located in a preserve owned and managed by the California Native Plant Society (CNPS), has fluctuated between 200 and 300 plants. Plants have recently expanded onto an adjacent parcel of private land to the east, where 70-100 plants were found in 1993.


The natural population of C. imbricata is at risk due to proposed land use conversion and mowing for fire control, while the planted population is threatened by damage associated with trespassers collecting rare plants found in the preserve. Both populations are also susceptible to adverse impacts from random events.

The type locality of C. imbricata along the roadside at Pitkin Ranch was extirpated prior to 1974, as a probable result of changes in land use or roadside maintenance. Another Sonoma County population of this taxon was extirpated as a result of tree farming and weed control activities. The sole remaining natural population of C. imbricata is threatened by conversion of land to agriculture and inadvertent mowing of its habitat, even though the Nature Conservancy has entered into a verbal conservation agreement with the landowner for the protection of this population. However, this location of C. imbricata was inadvertently mowed before seed set in 1989 and 1991, reducing the seed production and number of plants in subsequent years. This mowing for fire control during the reproductive cycle of C. imbricata has reduced the size of this population by a third.

The other population of C. imbricata is a planted on a preserve owned by the CNPS. C. imbricata is attractive to plant collectors and incidents of overutilization and illegal collection of this species have occurred in the past. Although CNPS has attempted to discourage unauthorized collection by fencing the preserve and by not publicizing the exact location of the site, trespassers have damaged the fence, trampled the vegetation, and collected C. imbricata seeds on several occasions.

Conservation and Recovery

The Vine Hill Clarkia only survives in one natural habitat and a nearby planted population in a 1.5 acres (0.6 hectares) preserve on private land owned by the CNPS. The non-protected critical habitat is on private land, and is potentially at risk from conversion or disturbance. This critical habitat should be protected by acquiring the habitat and establishing an ecological reserve, or by negotiating conservation easements with the landowners. The populations of the Vine Hill Clarkia should be monitored, and research undertaken into its ecological needs. Additional populations should be established in suitable habitat in the vicinity of the existing ones.


U. S. Fish and Wildlife Service
Sacramento Fish and Wildlife Office
Federal Building 2800
Cottage Way, Room W-2605
Telephone: (916) 414-6600
Fax: (916) 460-4619

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


U.S. Fish and Wildlife Service. 22 October 1997. "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for Nine Plants From the Grasslands or Mesic Areas of the Central Coast of California." Federal Register 62(204): 54791-54808.