Chorizanthe robusta var. robusta Chorizanthe robusta var. hartwegii
|Listed||February 4, 1994|
|Description||Wiry, annual herb with medium-sized to large notched, pinkish flowers growing in a dense cluster.|
|Habitat||Sandy and gravelly soils in the southern Santa Cruz Mountains.|
|Threats||Residential and golf course development, agricultural land conversion, sand mining.|
The robust spineflower, Chorizanthe robusta var. robusta, is a wiry, annual herb with large notched, white to pinkish flowers growing in a dense cluster. The shrub grows in a variety of postures, from erect to spreading or growing flat along the ground.
The robust spineflower's closely related species is Scotts Valley spineflower (C. robusta var. hartwegii ), which has medium-sized pinkish flowers growing in a dense cluster. The inner and outer petal-like sepals (green coverings of the flower) are equal in length and are lobed rather than fringed. The flowers's filaments are free, and there are three to nine stamens. There are six bracts below the flowers: three are toothed with the alternating three shorter. The shrubs can grow along the ground or erect, covered with short hairs.
The robust spineflower is endemic to sandy soils of coastal habitats in southern Santa Cruz and northern Monterey Counties. The inner rim of Monterey Bay is characterized by broad, sandy beaches backed by an extensive dune formation. Just inland from the immediate coast, maritime chaparral occupies areas with well-drained soils. Coastal dunes and coastal scrub communities exist along the inner rim of Monterey Bay.
Scotts Valley spineflower occurs on Purisima sandstone, with bedrock overlain with a thin soil layer that supports a meadow community comprised of herbs and low-growing grasses. The presence of certain associated species—such as toad rush (Juncus bufonis ), sand pigmyweed (Crassula erecta ), mosses, and lichens—suggest a high seasonal moisture content. Where the plant occurs on Santa Cruz mudstone, the bedrock is mixed with rock debris and a thin soil layer supporting a meadow community of herbs and grasses. This soil condition is somewhat different from the Purisima sandstone, with a lesser frequency of toad rush, pigmyweed, and lichens.
The only known populations of Scotts Valley spineflower occur in Scotts Valley in the Santa Cruz Mountains north of the city of Santa Cruz. Virtually the entire population resides on four parcels, all privately owned.
The only known populations of the robust spine-flower occurs northeast of the city of Santa Cruz on property owned by the University of California.
Shortly after the species was rediscovered in 1989, the total number of individuals was estimated to be 6,000. Results of 1992 surveys were that two populations on developments named Glenwood Estates totaled between 30,000 and 100,000 individuals. The numbers of this annual plant are expected to fluctuate from year to year, depending on climate conditions.
The robust spineflower populations are known from Sunset State Beach. In 1988 the population was believed to be about 5,000. Smaller populations of a few hundred each are near Manresa State Beach and on property owned by the city of Santa Cruz.
Populations of the robust spineflower in coastal dune and coastal scrub habitats were affected by residential development, recreational use, and the introduction of non-native species.
The only known populations of Scotts Valley spineflower occur in Scotts Valley in the Santa Cruz Mountains north of the city of Santa Cruz. Virtually the entire population resides on three parcels, all privately owned. Two parcels are currently proposed for a residential development and golf course named Glenwood Estates Development. Although the developers plan to set aside a portion of the habitat, the reserves may be affected by the application of pesticides, herbicides, and fertilizers on the adjacent golf course. The third parcel was scheduled for residential development but the ownership was transferred to a software development firm that intends to build its headquarters on the site.
The introduction of non-native plants to the coastal dunes for the purpose of sand stabilization adversely affected the native dune flora. Such introduced species as European beach grass, seafig, and iceplant invaded dune habitats and outcompeted native flora.
Conservation and Recovery
Management plans for the robust spineflower at Sunset State Beach have not yet been developed. Sunset State Beach has the largest known population, numbering 5,000 individuals in 1988. Smaller populations of a few hundred each near Manresa State Beach and on property owned by the city of Santa Cruz are not currently protected. The city will be developing a management plan to manage the property as a "low impact" park, and intends to protect habitat for the plant. A patch of 300 individuals located at Manresa State Beach could be relocated.
One of the four habitats for Scotts Valley spine-flower was scheduled for residential development but the ownership was transferred to a software development firm that intends to build its headquarters on the site. The firm, Borland Corp., indicated that pending expansion, it intended to set aside the species habitat. It still may be threatened by secondary impacts.
As proposed, the Glenwood Estates Development would destroy numerous small colonies of C. robusta var. hartwegii, but would set aside several reserves for the densest concentration of the plants. These reserves would be left as small islands within the golf course portion of the project.
Each of the proposals for development has included plans for setting aside preserve areas, but the U. S. Fish and Wildlife Service has advised the city of Scotts Valley that the preserve designs are inadequate to maintain long-term viability of the species.
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
U. S. Fish and Wildlife Servic
Ventura Fish and Wildlife Office
2493 Portola Rd., Suite B
Ventura, California 93003-7726
Telephone: (805) 644-1766
U. S. Fish and Wildlife Service. 4 February 1994. "Determination of Endangered or Threatened Status for Three Plants and Threatened Status for One Plant from Sandy and Sedimentary Soils of Central Costal California." Federal Register 59 (24): 5499-5511.
"Robust Spineflower." Beacham's Guide to the Endangered Species of North America. . Encyclopedia.com. (November 13, 2018). https://www.encyclopedia.com/environment/science-magazines/robust-spineflower
"Robust Spineflower." Beacham's Guide to the Endangered Species of North America. . Retrieved November 13, 2018 from Encyclopedia.com: https://www.encyclopedia.com/environment/science-magazines/robust-spineflower
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