CPC Plant Profile: Santa Cruz Island Rockcress
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Plant Profile

Santa Cruz Island Rockcress (Sibara filifolia)

This shot shows the plant in situ. Photo Credit: Denise Knapp
  • Global Rank: G2 - Imperiled
  • Legal Status: Federally Endangered
  • Family: Brassicaceae
  • State: CA
  • Nature Serve ID: 142991
  • Date Inducted in National Collection: 09/18/2021

Sibara filifolia, a small annual herb in the mustard family (Brassicaceae), is only found on San Clemente island, part of the Channel Islands of southwestern California. The plant reaches 38cm in height and produces pinkish-purple flowers that bloom from March to April (USFWS 1997). This species has been extirpated from other islands as a consequence of overgrazing by feral goats, pigs and sheep (USFWS 1995). The U.S. Fish and Wildlife Service listed Sibara filifolia as endangered in August of 1997 (USFWS 1997).

Participating Institutions
  • 09/01/2020
  • Orthodox Seed Banking

Based on an September 2020 extract of the California Plant Rescue Database, California Botanic Garden holds 5 accessions of Sibara filifolia in orthodox seed collection. There are as many as 192920 seeds of this species in their collection - although some may have been used for curation testing or sent to back up.

  • 08/05/2020
  • Seed Collection

Based on an August 2020 extract of the California Plant Rescue Database, California Botanic Garden has collected 4 seed accessions of Sibara filifolia from 2 plant occurrences listed in the California Natural Diversity Database. These collections together emcompass 8 maternal plants

Nature Serve Biotics
  • 05/02/2017

Currently known only from at least 3 sites, located in a small area on 1 of the Channel Islands of southern California; thought to have been widely distributed in this archipelago formerly. A 2002 report describes a population on a second Channel Island in an area protected from feral goats. Extirpated on at least 1 island by intensive browsing by non-native feral goats. Feral herbivores have been removed from San Clemente Island, where the extant plants are located.

  • 01/01/2010

Grazing of domesticated animals and introduced non-native plants have been the greatest historical threat. Goats were present on San Clemente Island as early as 1827. Sheep grazing occurred on many of the islands from the late 1800's to the early 1900's w

  • 01/01/2010

There are less than 500 individuals remaining on San Clemente Island (USFWS 1995).

  • 01/01/2010

Allozyme variation in Sibara filifolia is being studied by Dr. Kaius Helenurm (2001) and his graduate student Sarah Helm at the University of South Dakota. Helenurm's study (2001) obtained electrophoretic data for 29 allozyme loci from individuals collected as seed from the three known populations on San Clemente Island. Overall levels of genetic variation were low. Only two polymorphic loci were observed, resulting in low number of alleles per locus (1.01), average observed heterozygosity (0.006) and average expected heterozygosity (0.009) for populations. Interestingly, all polymorphism occurred in just one of the three populations, in spite of their close proximity. Most variation on San Clemente Island is thus found within rather than among populations (GST = 0.144), and there is significant differentiation among populations (FST = 0.145). Gene flow is estimated as Nm = 0.41 based on private alleles and Nm = 1.49 based on FST. The differentiation of populations and low level of gene flow suggests that genetic drift is a potent force in these small populations and may further reduce genetic variation. RAPD and quantitative genetic studies are recommended to further evaluate these populations and the long-term prospects for this species.

  • 01/01/2010

In the 1990's the U.S. Navy removed approximately 20,000 feral goats and pigs from San Clemente Island (USFWS 1995). Developing and implementing a management plan that includes fire protection, population monitoring and the establishment of new populations will be necessary for this species recovery.

  • 01/01/2010

Habitat protection and the promotion of self-sustaining populations are primary concerns. Understanding reproductive biology will aid in the establishment of new populations.


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Taxon Sibara filifolia
Authority (Greene) Greene
Family Brassicaceae
CPC Number 3953
ITIS 23304
Common Names island rock cress | Santa Cruz Island rock cress | Santa Cruz Island winged rockcress
Associated Scientific Names Sibara filifolia | Arabis filifolia | Cardamine filifolia
Distribution Historically, Sibara filifolia was found on Santa Cruz, San Clemente and Santa Catalina Islands of the coast of southwestern California. Today it is only found on San Clemente Island (USFWS 1995). A r
State Rank
State State Rank
California S2

The Channel Islands consist of igneous and sedimentary rocks formed by tectonic uplift (USFWS 1995, USFWS 1997). San Clemente Island, the most southern island, is characterized by high plateaus and deep cliff sides (USFWS 1995).

Ecological Relationships

Although ecological relationships are unknown, Sibara filifolia is associated with Opuntia prolifera (Cholla), Selaginella bigelovii (spike-moss), and Lotus argophyllus (birds-foot trefoil) (USFWS 1995).

Common Name Name in Text Association Type Source InteractionID
Self Pollinated Confirmed Pollinator Link

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