National Collection of Imperiled Plants

CPC National Collection Plant Profile

Photographer:

Dieter Wilken

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CPC National Collection Plant Profile

Arabis hoffmannii

Family:	Brassicaceae
Common Name:	Hoffmann's rock cress
Author:	(Munz) Rollins
Growth Habit:	Subshrub, Forb/herb
CPC Number:	178

Distribution
Protection
Conservation
References

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Photographer: Dieter Wilken
dwilken[at]sbbg.org

Arabis hoffmannii is Not Sponsored

Primary custodian for this plant in the CPC National Collection of Endangered Plants is:

Santa Barbara Botanic Garden

Dieter Wilken, Ph.D. contributed to this Plant Profile.

Arabis hoffmannii

Less than 150 plants in 3 populations are known to exist. Two populations each have less than 5 reproductive plants annually. The remaining population may have as many as 30 reproductive individuals in any one year. Although reproductive plants produce many fruits and seeds, most of the seeds are dispersed to adjacent, unfavorable sites. The primary threats to survival and recovery are feral pig activity, subsequent erosion, and competition from alien grasses.

Plants are monocarpic, growing vegetatively for 3-5 years before flowering, fruiting and dying (Wilken 1996). Reproductive plants grow up to 70 cm tall, each with about 40 fruits that contain about 125 seeds. The minute seeds are slightly winged and dispersed by wind. Vegetative plants less than 3 years old have solitary leaf rosettes about 1-3 cm wide and less than 5 cm tall. During the summer months the uppermost rosette leaves curve upward and become dormant, surrounding the growing tip. Reproductive leaf rosettes vary from 10-15 cm wide, and bear single erect racemes with small white to lavender flowers.

Distribution & Occurrence

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State Range

California

Habitat

Sandy to rocky soils of open sites in coastal shrublands, often on ledges or cliff ledges. Associated species include Coreopsis gigantea, Hazardia detonsa, Eriogonum arborescens, and Adenostoma fasciculatum at one site. Populations are found near the coast, usually where summer fog dominates during the late afternoon or night.

Distribution

Santa Cruz and Santa Rosa Islands, Santa Barbara County, California. A historic report from Anacapa Island has not been substantiated and is probably erroneous.

Number Left

Only 3-4 populations are known; 2-3 on Santa Cruz Island and one on Santa Rosa Island. The largest population, with an annual average of 30 reproductive individuals, occurs on Santa Cruz Island. The remaining populations are composed of 0-5 reproductive individuals in any one year. A third locality on Santa Cruz Island has remained inaccessible and unmonitored for at least 5 years.

Protection

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Global Rank:	G1	10/24/2005	Guide to Global Ranks
Federal Status:	LE	7/31/1997	Guide to Federal Status
Recovery Plan:	Yes	9/26/2000

State/Area Protection

	State/Area	Rank	Status	Date
	California	S1.3	5

Conservation, Ecology & Research

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Ecological Relationships

Plants require fine-grained soils, shade, and summer moisture from foggy nights. Plants are self-compatible. Flowers are capable of self-pollination but insect visitation, mostly by bee flies (Bombyliidae), enhances seed set. Average plants produce about 3,000 light seeds, which are dispersed by wind as the fruits slowly dehisce. (Wilken 1995)

Threats

As listed in the recovery plan for thirteen plant taxa from the northern channel islands (USFWS 2000):
� Feral pig rooting activities directly affecting the Hoffman's rock cress plants.
� Soil erosion following feral pig activity indirectly affecting the health of the plants and their habitat.
� Competition from alien weeds (primarily grasses).
� Catastrophic loss of small and vulnerable populations.

Current Research Summary

Ongoing research by the Santa Barbara Botanic Garden has focused on reproductive biology and ecological requirements. Seedling cohorts show high mortality. Short-term drought, caused by high temperatures and lack of a maritime layer, has limited survival of seedlings and one-year old plants in some years since 1995. Most reproductive plants occur in close proximity to shrubs, suggesting that shade is important to survival during the first 2 years of growth. (Wilken 1996)

Current Management Summary

Santa Rosa Island is managed by the National Park Service. The population on Santa Rosa Island occurs on a narrow ledge near a road. Sites on Santa Cruz Island occur on lands owned and managed by The Nature Conservancy. The latter, in cooperation with the National Park Service, is developing a plan for feral pig removal and reduction of exotic weeds. However, no short-term measures have been taken to protect populations from pig rooting.

Research Management Needs

� Protection of current populations on Santa Cruz Island.
� Genetic analyses of populations, including variation among annual cohorts.
� Collection of seeds from the population on Santa Rosa Island.
� Surveys for undiscovered populations and for sites suitable for reintroduction.

Ex Situ Needs

Studies of seed longevity under both short-term and long-term cold storage conditions.

References

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Books (Single Authors)

Rollins, R.C. 1993. The Cruciferae of continental North America: Systematics of the mustard family from the Arctic to Panama. Stanford, California: Stanford University Press. 976p.

Books (Sections)

Kartesz, J.T. 1999. A synonymized checklist of the vascular flora of the U.S., Canada, and Greenland. In: Kartesz, J.T.; Meacham, C.A., editors. Synthesis of the North American Flora, Version 1.0. North Carolina Botanical Garden. Chapel Hill, NC.

Books (Edited Volumes)

James C. Hickman, Editor. 1993 The Jepson manual: Higher plants of California. Berkeley: University of California Press. 1400p.

Electronic Sources

USFWS. (2002). Threatened & Endangered Plants Within Ventura Field and Wildlife Office Area of Responsibility. U.S. Fish and Wildlife Service, Ventura Fish and Wildlife Office. http://ventura.fws.gov/plant.html. Accessed: 2002.

Journal Articles

USFWS. 1995. Proposed rule for 16 plant taxa from the northern Channel Islands, California. Federal Register. 60, 142: 37993-38010.

USFWS. 1997. Final rule for 13 plant taxa from the northern Channel Islands, California. Federal Register. 62, 147: 40954-40974.

USFWS. 1997. Notice of Reopening of Comment Period on Proposed Endangered Status for Sixteen Plants from the Northern Channel Islands of California. Federal Register. 62, 14: 3263.

Reports

1995. TNC "Plants in Need" List. The Nature Conservancy. p.3.

USFWS. 2000. Thirteen plant taxa from the northern Channel Islands Recovery Plan. Portland, Oregon: U.S. Fish & Wildlife Service, Region 1. p.93.

Wilken, D. 1996. Reproductive strategies of four plants restricted to the northern California Channel Islands. Report to the U.S. Fish and Wildlife Service. Santa Barbara Botanic Garden. p.42.

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This profile was updated on 3/4/2010