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Howell's spineflower
Chorizanthe howellii

General Information

Official Status: Endangered, the Howell’s spineflower is federally listed under the Endangered Species Act, and listed as Endangered in California.

Date Listed: June 22, 1992; Federal Register 57 FR 27848-27859 (pdf, 1.4 MB)

Critical Habitat: Critical habitat has not been designated for this species.

Recovery Plan: The Recovery Plan (pdf, 11 MB) for Howell’s spineflower was approved in March 1998.

5-Year Status Reviews:

2011 5-Year Status Review

2007 5-Year Status Review


Howell's Spineflower, Photo Credit: Dave Imper, USFWS

Howell's spineflower

Photo Credit: Dave Imper, USFWS

arrow button Photo Gallery for Howell's spineflower

Identifying Characteristics:

Howell's spineflower is an herbaceous annual member of the buckwheat family (Polygonaceae). The plants are 1 to 3.9 inches tall and 3.9 to 20 inches across. The basal leaves are 0.4 to 1.2 inches long and 0.2 to 0.6 inches wide. Flowers range 0.1 to 0.2 inches long. What appears to be a spiny flower is in fact mostly the involucre that surrounds the flower, tipped with six brown, straight spines. The distinguishing morphological feature of Howell’s spineflower is its straight awns.

Current Geographic Range:

The current known global distribution of Howell’s spineflower extends from the Tenmile River, north of the City of Ft. Bragg, Mendocino County, California, south approximately 5.4 miles to Virgin Creek, and as much as 0.5 mile inland from the Pacific Ocean.  Nearly the entire distribution occurs within MacKerricher State Park.  A small portion is in private ownership.

Life History:

As an annual species, Howell’s spineflower completes its life cycle in one year. Dispersal of seeds is facilitated by the spines (on the involucres) which attach the seed to passing animals. 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 and highly mobile open sand. The species may form 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 blooms from May through July.

General Habitat Characteristics:

Howell’s spineflower occurs in young coastal dunes and adjacent sandy soils of coastal prairies at elevations ranging from sea level to 120 feet. In coastal dunes, it is associated with sand verbena and Menzies' wallflower. In coastal prairie habitat, associated plants include non-native grasses, sweet vernalgrass, velvetgrass, Mendocino coast paintbrush, and northcoast phacelia.

Howell’s spineflower generally occupies habitat referred to as early successional.  Some kind of disturbance (e.g., wind exposure, sand deposition, limited foot traffic) may be necessary to prevent encroachment and eventual replacement by other species.   By no coincidence, much of the occupied habitat now occurs adjacent to, but not within, pedestrian or horse trails.  However, some of the largest stands are located within semi-stabilized dune swales, which appear to receive little foot traffic.  Howell’s spineflower in general does not tolerate a high level of competition for seedling establishment.  In some cases, Howell’s spineflower effectively colonizes areas in which iceplant has died or been pulled, if the remaining mulch is not too deep.  In 2005 this observation led to a study funded under a ESA Section 6 grant, to study the conditions under which a routine program of iceplant removal might contribute to reliable periodic regeneration of suitable habitat, and thus recovery of the species.
Population and Habitat Status:

Within MacKerricher State Park, a survey conducted in 2001 mapped some 255 occupied habitat polygons, up to 0.73 acres in area, and totaling some 7.3 acres within about an overall 125 acre area of dunes and bluff.  No statistically valid estimate of the population has been made.  Based on a small number of sample plots surveyed in 2002, the population that year may have exceeded 3 million individual plants.  While that estimate appears large, we have little information available to put the population size in a meaningful context.  As an annual species, Howell’s spineflower responds almost immediately to changes in its environment.  A persistent seedbank in the soil can mitigate this dependence to some extent, but there is no information indicating whether Howell’s spineflower forms such a seedbank.  Howell’s spineflower is capable of rapid exploitation of habitat in some cases, such as following removal of iceplant.  However, very large declines in the density of plants have also been observed, even within a single season, following encroachment by invasive species or changes in recreational use.  Therefore, more information is needed on natural population fluctuations, the impacts of recreational disturbance and how that is changing, the rate of encroachment by invasive species, and in particular, the overall population trend, in order to determine the  viable population size for this species.  


Howell’s spineflower is known historically from coastal dunes north of Fort Bragg.  However, little is known about the historic number or size of the populations before human impacts, since the species was not distinguished taxonomically until after civilization altered much of its historic habitat.  While the current population estimate suggests the taxon may not be at as great a risk as originally thought, two factors must be taken into account.  The unrelenting encroachment by invasive species such as iceplant, European beachgrass, and burclover, can rapidly eliminate Howell’s spineflower habitat if unchecked.  At the same time, the continuous recreational pressure at MacKerricher State Park, including pedestrian and equestrian traffic, while in many circumstances may be beneficial toHowell’s spineflower, has the potential to rapidly and severely degrade or eliminate much of its habitat.  Recreational pressure in the park is expected to increase as the surrounding residential population grows and access to the park is improved. 

Due to the overwhelming threat posed by invasive species, and the fact that some kinds of human disturbance counter this threat, location of the majority of Howell’s spineflower within MacKerricher State Park, can be viewed as a tremendous opportunity for permanent protection and management of the species, if managed wisely.  Ultimately, the recovery of Howell’s spineflower depends on compatible management of recreational activities and a permanent control program for invasive species.
Conservation Needs:

Further understanding is needed on how to best accommodate the current and expected increase in recreational use while maintaining a stable population of Howell’s spineflower, and how to best restore itshabitat.  In addition, given that the threat from invasive species is not likely to ever go away, a means is needed for ensuring that the monitoring and responsive management necessary to maintain Howell’s spineflower in perpetuity is conducted.  Recovery efforts for this species largely consist of refinement and implementation of permanent Howell’s spineflower habitat management, which must include both invasive species control and careful management of recreational activities. 

The principle remaining recovery tasks include:

1. California State Parks and the U.S. Fish and Wildlife Service should continue to pursue opportunities for acquisition or protection of crucial habitat adjacent to the park.

2. Efforts need to continue the removal of iceplant and European beachgrass, and explore ways to implement a permanent invasive species monitoring and response program.  The two agencies must pursue opportunities to secure permanent funding which ensures periodic monitoring and habitat restoration efforts are conducted in perpetuity.  Such funding cannot be subject to unpredictable State Parks staffing level and budgets if recovery is to be assured.  

3. A baseline population estimate is also needed as soon as possible, to be repeated at periodic intervals.  At the same time, periodic remapping of occupied habitat is needed to detect overall changes in the distribution of Howell’s spineflower, and provide feedback on whether current recreation management is consistent with maintaining the species. 

4. Since habitat disturbance is known to be a necessary element in the ecology of Howell’s spineflower, quantitative data are needed linking specific recreational use to response by the species. 
Related Documents:

No other documents other than those listed in the general information section above.

Other Informational Weblinks:

Last updated: December 13, 2011

Arcata Fish and Wildlife Office, 1655 Heindon Road, Arcata, California 95521, USA
Tel: (707) 822.7201 Fax: (707) 822.8411