Island Barberry

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Island Barberry

Berberis pinnata ssp. insularis

ListedJuly 31, 1997
FamilyBerberidaceae (Barberry)
DescriptionA low shrub with large leaves that are divided into five to nine glossy green leaflets and has clusters of yellow flowers at its branch tips.
HabitatMoist, shaded canyons on Santa Cruz Island.
ThreatsHabitat destruction and degradation by introduced mammalian herbivores and invasive alien plants.


Berberis pinnata ssp. insularis (island barberry) was described in 1952 from a specimen collected 20 years earlier "west of summit of Buena Vista Grade (also known as Centinela Grade), interior of Santa Cruz Island." This taxon was included in the genus Mahonia in 1981 because the leaves are compound, in contrast with the simple leaves of Berberis. However, in 1982 the argument was made that this one character was insufficient to defend Mahonia as a distinct natural group, and many subsequent treatments have included all North American taxa previously referred to Mahonia as Berberis. This taxon has been treated as Berberis pinnata ssp. insularis since 1974. Berberis pinnata ssp. insularis is a perennial shrub in the barberry family (Berberidaceae). The plant has spreading stems that reach 5-25 ft (2-8 m) high, with large leaves divided into five to nine glossy green leaflets. Clusters of yellow flowers at the branch tips develop into blue berries covered with a white bloom (waxy coating). Because new shoots can sprout from underground rhizomes, many stems may actually represent one genetic clone. Recent research indicates that, although the plant is genetically self-compatible, it requires insect visitation for pollination. Each flower produces from two to three seeds, but in seed germination experiments only eight out of 40 seedlings survived long enough to produce secondary leaves. Observations on the one plant in upper Canada Christy indicated that, of over 100 flowers that were in bud in January 1996, only seven immature fruit had developed by May 1996.


Island barberry inhabits moist, shaded canyons on Santa Cruz Island.


Documentary evidence indicates that this taxa was quite common on Santa Cruz Island in the 1930s. Berberis pinnata ssp. insularis is currently known from three small populations on Santa Cruz Island. Several individuals were found "in Elder canyon that runs from west into Canada de la Casa" on Santa Rosa Island in 1930. No plants have been found on Santa Rosa Island since that time despite government and private surveys between 1993 and 1996. Berberis pinnata ssp. insularis was collected on West Anacapa Island in 1940, but the plant was not found there again until 1980, when one clone was found in Summit Canyon associated with chaparral species, including poison oak (Toxicodendron diver-silobum ), monkeyflower (Mimulus aurantiacus ), coyote bush (Baccharis sp.), goldenbush (Hazardia detonsus ), island alum-root (Heuchera maxima ), and wild cucumber (Marah macrocarpus ).

A 1994 survey found that the clone had died, and Berberis pinnata ssp. insularis is therefore believed to be extirpated from Anacapa Island. The three known populations of Berberis pinnata ssp. insularis occur on Santa Cruz Island. One population on the north slope of Diablo Peak comprises 24 large stems and 75 small stems; this number of stems may represent one or several clonal individuals. In 1979, a second population near Campo Raton (Canada Cristy) was estimated to be fewer than 10 individuals, but in 1985 only one plant was seen. Habitat for the plant was systematically searched recently in the Campo Raton area and two individuals were located. Both plants were in danger of uprooting from erosion and only one plant flowered but it did not set fruit. The size of the third known population, at Hazard's Canyon, has not been determined due to inaccessibility, but it is estimated that there were between one and seven plants at this location. Berberis pinnata ssp. insularis can be found in moist, shaded canyons on Santa Cruz Island.


Berberis pinnata ssp. insularis is threatened by soil loss and habitat alteration caused by feral pig rooting. Although ex-situ clones have been established from vegetative cuttings, populations in the field show no signs of successful sexual reproduction. The soil from around the roots of Berberis pinnata ssp. insularis on Santa Rosa Island is actively eroding. The collection of whole plants or reproductive parts of Berberis pinnata ssp. insularis could adversely affect the genetic viability and survival of this taxa.

Conservation and Recovery

The island barberry only survives as three tiny populations on Santa Cruz Island. The broader habitat on the island is being conserved in a relatively natural condition in the Channel Islands National Park, and by the Nature Conservancy, a private conservation organization. However, the island bar-berry and other rare plants are severely threatened by the feeding of sheep and other introduced mammals. The protection of the endangered bar-berry requires that these herbivores be reduced or eliminated from its habitat. The abundance of invasive alien plants should also be reduced or eliminated, because they are providing intense competition to native species. The populations of the island barberry should be monitored, and research undertaken into its biology and habitat needs, including methods of management that would benefit the endangered plant. A captive-propagation program should be developed, to provide stock for out-planting to supplement the tiny natural population, and to reestablish populations on nearby islands from which the barberry has been extirpated.


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


U.S. Fish and Wildlife Service. 31 July 1997. "Endangered and Threatened Wildlife and Plants; Final Rule for 13 Plant Taxa From the Northern Channel Islands, California." Federal Register 62(147): 40954-40974.

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Island Barberry

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