|Listed||June 22, 1992|
|Description||Shaggy-haired, short annual herb with spatula-shaped long leaves.|
|Threats||Habitat destruction, competition from introduced plants, off-road vehicle damage.|
Howell's spineflower (Chorizanthe howellii ) is a shaggy-haired, short annual herb with long, spatula-shaped basal leaves and spreading to decumbent stems that branch from the base. Flowers of this buckwheat appear from May through July and are white to rose in color. The flowers measure 0.14-0.18 in (3.6-4.6 mm). This species' flowers possess tepals, involucres and involucral teeth, and awns, which distinguish it from other Chorizanthe.
Howell's spineflower is an annual species, completing its life cycle within one year. Dispersal of seeds is facilitated by the spines (on the involucres), which attach the seed to passing animals. Howell's spineflower blooms from May through July
Howell's spineflower is associated with the California coastal redwood belt, Siskiyou-Trinity area, central California coastal valleys, and the central California coast range. Broadly, these regions have 1) an elevation from sea level to 2,950 ft (899 m); 2) an average annual precipitation of 11.8-33.5 in (300-850 mm) distributed throughout the year; 3) perennial streams and lakes distributed throughout them and glacial and alluvial deposits in the valley yielding large quantities of water; 4) dominant soils that are umbrepts, xerults, xerolls, humults, or ochrepts, well drained and gently sloping to very steep soils, with a mesic to xeric temperature regime and a mixed mineralogy. The erosion hazard is high in this area and is stabilized only by plant cover. Much of this land is federally owned and the remaining is used for lumbering, grazing, wildlife habitat, and recreation.
The species occurs in recent coastal dunes and adjacent sandy soils of coastal prairies (ancient dune soils) at elevations ranging from sea level to 120 ft (37 m). In coastal dunes, it is associated with sand verbena and Menzies' wallflower. In coastal prairie habitat, associated plants include two non-native grasses, sweet vernalgrass and velvetgrass, and two species of special concern, Mendocino coast paint-brush and northcoast phacelia.
The preference of this species for vegetation gaps or sparsely-vegetated areas on sandy substrate allows seedlings to establish in areas that are relatively free from other competing native species. It seldom occurs or persists in dune areas of dense European beachgrass cover, dense native vegetation cover, or bare, highly mobile sand. It is unknown whether this species forms a dormant soil seed bank.
The species 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 winter rains.
Howell's spineflower is known, both historically and in the early twenty-first century, from coastal dunes north of Fort Bragg in Mendocino County, California. Three populations totaling 23,700 individuals are known in the dune system south of Ten Mile River. One extended population is in MacKerricher State Park; three additional populations are on private lands. It occurs sporadically within an area of more than 125 acres (51 hectares) on portions of the United States Geological Survey, Fort Bragg, and Inglenook quadrangles. The largest occurrence contained more than 20,000 individual plants as reported in 1989; however, in 1994 the entire state park population was estimated to be much smaller.
Howell's spineflower has most likely always been a narrow endemic and has become endangered by artificial stresses placed on what were probably naturally small populations. Little is known about the historic number or size of populations before human impacts because the taxon was not distinguished until after substantial alteration to its ecosystem had occurred. It is mostly restricted to MacKerricher State Park, where recreational and maintenance activities are the main threats to its continued existence.
Recreational activities historically included off-road vehicle use and hiker and equestrian traffic that caused habitat degradation. Several colonies will be destroyed by a trail along the entire fore-dune planned at MacKerricher State Park. The indirect effects of a maintained. stabilized road on sand transport and plant community succession are uncertain. Stabilization of foredunes in other dune systems often results in reduced sand transport landward and accelerated succession to closed, disturbance-intolerant vegetation. This could also adversely affect Howell's spineflower. Trail improvements would probably increase pedestrian access to dunes and increase the risk of trampling to more remote populations of Howell's spineflower. In addition, invasion of the dune habitat by European beachgrass, burclover, and the non-native plant variously called sea-fig, fig-marigold, or iceplant—all of which can outcompete and supplant native species—is a serious threat to Howell's spineflower. Trail disturbance is likely to facilitate the establishment of these invasive plants.
Conservation and Recovery
The MacKerricher State Park Ten Mile Dunes Restoration Plan describes measures to protect and enhance the habitat for Howell's spineflower within the park. Conservation measures undertaken for Howell's spineflower have included 1) the elimination of off-road vehicle use, 2) limited management of invasive non-native plants, including iceplant, European beachgrass, and burclover, and 3) the augmentation of populations of Howell's spineflower and Menzies' wallflower. MacKerricher State Park has redirected an equestrian trail away from occupied habitat.
An archaeological dig conducted by the University of California, Davis, in 1989-90 disturbed occupied habitat. Seed was collected in the summer of 1989 before the dig began. Plants were grown at the California Conservation Corps (CCC) Napa nursery and outplanted by the CCC in February 1990. The project had very limited success.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Avenue
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
Carlsbad Fish and Wildlife Office
2730 Loker Ave. West
Carlsbad, California 92008-6603
Telephone: (760) 431-9440
Fax: (760) 431-9624
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.