Santa Cruz Tarplant

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Santa Cruz Tarplant

Holocarpha macradenia

ListedApril 19, 2000
FamilyCompositae (Asteraceae)
DescriptionAromatic annual herb with yellow flowers.
HabitatGrasslands and prairies on coastal terraces.
ThreatsHabitat alteration and destruction from development.


The Santa Cruz tarplant is a rigid, aromatic annual herb with a main stem that is 4-20 in (10-50 cm) tall, with lateral branches that come to the same height. Lower leaves are broad and linear, up to 5 in (12 cm) long. The upper leaves are smaller, margins are rolled back and truncated by a craterform gland. The flower head is yellow and surrounded underneath by individual bracts containing 25 stout gland-tipped projections.

This tarplant is distinguished from others in its genus by its numerous ray flowers and black anthers.


Populations of the Santa Cruz tarplant occur on gently sloping terrace platforms that are separated by steep "gulches" where alluvial deposits are on top of the typically sandy clay terrace soils. These deposits are critical because they hold water longer into the growing season.

Associates are now non-native grasses such as wild oats, Mediterranean barley, and bromes. Natural associates are being displaced.


The historical habitat of the Santa Cruz tarplant once consisted of 865,000 acres (350,000 hectares) of grasslands and prairies found on coastal terraces below 330 ft (100 m) in elevation. Distinct populations were also found in "low dry fields" in the San Francisco Bay area. Associates included native herbaceous species and grasses, needlegrass, and Californian oatgrass.

The Santa Cruz tarplant is currently known from a total of 20 populations, 12 native and 8 from experimental seeding. Eleven of the native populations are in Santa Cruz County, six around the city of Santa Cruz, and five around the city of Watsonville. One population is found in Monterey County just south of the city of Watsonville. Population sizes range from zero to millions. (Due to viable seedbanks, there can be years where no plants are counted.)

The eight populations established by seeding exist in the Wildcat Regional Park east of the San Francisco Bay area. Population sizes range from none to just over 300.


Primary threats to the Santa Cruz tarplant are habitat alteration and both residential and commercial development. Of the 12 native populations, six native populations are on private lands and either are slated for development or plans to develop are expected in the near future; one, which is the largest, is owned by Watsonville Airport which plans to expand in the near future; and colonies have been found on the Spring Hills Golf Course, but no conservation efforts have been agreed upon.

Three of the native sites are found on public land and are already severely impacted by secondary effects of nearby development.

Threats from residential development include inadvertent burning, mowing, trampling, and fragmentation. These allow for the entrance of non-native invasive species like French broom, eucalyptus, acacia, rattlesnake grass, and artichoke thistle to dominate the landscape.

Grazing in many of these sites has also been known to affect the area. Grazing speeds up the process by which non-natives enter the habitat area. Changes in hydrology and the lack of management plans exacerbate the problem.

Conservation and Recovery

Conservation measures have already begun for the Santa Cruz tarplant. New colonies have been established from seed. There is limited success in establishing a viable population via this process, but attempts to make it work will continue.

Seven of the 12 native populations have some plan for conservation. For example, the Watsonville Airport has mitigation plans for the tarplant, while other populations are protected because they are on public land. In one case, a homeowners association is taking steps to protect the tarplant via mowing, weed control, fencing, and removal of non-native species.

A recovery plan is being written for the Santa Cruz tarplant, which will further determine what steps need to be taken in order to protect this species' habitat in the future.


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

Ventura Fish and Wildlife Office
U. S. Fish and Wildlife Service
2493 Portola Road, Suite B
Ventura, California 93003-7726
Telephone: (805) 644-1766


United States Department of the Interior. 20 March 2000. "Endangered and Threatened Wildlife and Plants: Threatened Status for Holocarpha macradenia (Santa Cruz tarplant)." Federal Register 65 (54):14898-14909.

University of California, Berkeley. " Holocarpha macradenia." CalFlora Database Project: a botanical resource for California on the internet. ( Date accessed: July 11, 2000.

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Santa Cruz Tarplant

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Santa Cruz Tarplant