California Native Plant Society

Locally Rare Plants

Clarkia tembloriensis ssp. tembloriensis is a locally rare plant in Alameda County known only from Corral Hollow near the Lawrence Livermore Lab. However, this species is known from at least 5 other counties in California and would therefore be considered a locally rare species but would not be considered a California rare species.

CNPS has tracked plants that are rare from a statewide perspective since the late 1960's, and has been successful in gaining protection for these plants under the California Environmental Quality Act (CEQA) and other laws and regulations. Over 2,000 taxa are currently considered by CNPS to be rare statewide (see CNPS' Online Inventory of Rare and Endangered Plants of California). However, CNPS recognizes that the preservation of regional and local scales of genetic diversity is also very important. Due to the large size of our state and the rapid alteration and loss of natural habitats, many plant taxa that are too common from a statewide perspective to include in the CNPS Inventory are nonetheless declining rapidly.

What are locally rare species?

Locally rare species are those species that the scientific community considers sensitive or unique or that occur at the limits of their natural range within a specific region (also called peripheral populations). A variety of factors play a role in determining whether a species is considered locally rare. Species-specific characteristics, available suitable habitat, as well as land use activities and practices, all play a role in determining whether a species that is relatively common in one part of its range is rare in another part of its range.

Many plant populations are considered locally rare because they occur on the geographic edge of the species range. These peripheral populations are important because they often show morphological and ecological divergence and can be genetically distinct from the main population of the species. These character traits help contribute to the long-term survival of a species. Even very widespread taxa have been brought to near extinction in a short amount of time and peripheral plant populations can act as refugia for species. It has been shown that in species that undergo catastrophic range contractions, peripheral populations have greater survivorship than the core population.

Locally rare plants play an important role in helping to preserve the diversity of the species, as well as the gene pool of local flora. Locally rare plants also preserve the potential for the species to undergo speciation events and are often of scientific or historical importance. With all of the benefits associated with preservation and conservation of locally rare plant populations, CNPS encourages local chapters to establish their own locally rare plant program (see article by Dianne Lake below for additional information).

Arbutus menziesii is documented as occurring in at least 33 counties within California. However, southern Sierra Nevada and southern California counties are represented by only a few populations of this species. A. menziesii should be treated as locally rare in those counties in which it has 10 or fewer populations, which would likely include San Diego, Calaveras, Orange, Los Angeles, Ventura, San Benito, Amador, Riverside, Mariposa, and Tuolumne Counties.

Laws Governing the Protection of Locally Rare Species

Floristic botanists prefer to look at natural distribution patterns and influences when studying the range, distribution, and population characteristics of a species; however, few of our laws follow or consider the natural environment. Rather, our laws are made and enforced according to political boundaries, such as states, counties, and cities, and conservation efforts must therefore also work within those political boundaries. Because many laws, including CEQA, are implemented at the local level (county or city), it is not always appropriate to limit oneself to a statewide perspective on rarity. Use of the CNPS Inventory as part of the project impact assessment has become routine; however, it is also important to take into consideration those plants that are rare at the local level.

CEQA is one environmental law that is extremely important in rare plant conservation, including the conservation of species that are considered locally rare. While CEQA has rarely been used to date for the protection of locally rare plant populations, Article 9 of CEQA states that “special emphasis should be placed on environmental resources that are rare or unique to that region.” For this reason, it is important to provide agencies with local conservation tools so that project-related impacts on the flora within their jurisdiction and region can be better assessed.

CNPS' Involvement in Locally Rare Species

Two chapters and a botanic garden have had the foresight to set criteria defining local rarity and identify species that are rare locally. To date, three locally rare plant lists have been created. The CNPS East Bay Chapter's locally rare effort, led by Dianne Lake, has maintained a list of "unusual and significant" plants of Alameda and Contra Costa Counties since 1992 (now in its seventh edition). David Magney, formerly of the CNPS Channel Islands Chapter (now CNPS Rare Plant Program Manager), developed a list of locally rare taxa for Ventura County (now in its 22nd edition). The Ventura County list has been used by the Ventura County Planning Division to develop List of Locally Important Plants. In addition, at the request of the Channel Islands Chapter, Dieter Wilken (then at the Santa Barbara Botanic Garden) created a preliminary list of locally rare plants of Santa Barbara County and the four northern Channel Islands in that county.

In addition, CNPS has established a committee designed to discuss issues related to locally rare species, to develop methodologies, and to encourage the compilation and publication of more county-specific rare plant lists. This group has been named the Locally Rare Working Group. Key members of the Locally Rare Working Group include: David Magney, Dianne Lake, Gordon Leppig, and Jeffrey White, with additional members from around California helping with this project. Through their efforts, huge steps have been made to recognize the conservation concern associated with locally rare plants throughout California, with a goal of establishing lists of locally rare plants in each California county.

If you would like to participate in the Locally Rare Working Group or help put together a locally rare working group in your area, please contact David Magney () or Gordon Leppig () for further information.

Documents on Locally Rare Species

Menyanthes trifoliata is relatively common in the Sierra Nevada, but is extremely rare on the North Coast. On the North Coast, this species is extirpated from San Francisco County and is known from only one population each in Del Norte, Marin, and Mendocino Counties. It is also known from a population in Humboldt County that is presumed extirpated. M. trifoliata should be considered locally rare in these North Coast counties.

Geographic Discrepancies Between Global and Local Rarity Richness Patterns and Implications for Conservation, published in the journal Biodiversity and Conservation by Benjamin Crain, Jeffrey White, and Steven Steinberg uses an analysis of the flora of Napa County to identify locally rare plant species.   They use a 1-square-km grid system to determine plant distribution and commonness, then apply their results to the existing global and state Natural Heritage Network's Element Ranking System and those species found rarely in Napa County to identify gaps in identifying vulnerable species, with the goal to prevent local extinctions.

Categorizing Locally Rare Plant Taxa for Conservation Status, published in the journal Biodiversity and Conservation by Benjamin Crain and Jeffrey White examines the need for a specific rarity ranking level for local areas, such as counties, expanding upon their floristic work in Napa County.   They examine the appropriateness of modifying the Natural Heritage Network's Element Ranking System, combined with attributes of the World Conservation Union's Red List Criteria.   Crain and White recommend the creation of a "L" rank for locally rare plant species.

Conservation of Peripheral Plant Populations in California (PDF 223k) (by Gordon Leppig and Jeffery White)- an article (published in Madroño) that looks at the conservation value of locally rare species, describes regulatory methods to improve the conservation of those species, and develops a scheme to assess a population's conservation value.

How to Establish a Locally Rare Plant Program for your Chapter (PDF 51k) (by Dianne Lake)- a manual on how to get started creating a program in your Chapter devoted to locally rare plants.

Ventura County Rare Plants List (compiled by David Magney)- a checklist of the rare plants of Ventura County, which includes locally rare and uncommon taxa, as well as those plant taxa present in Ventura County that are considered rare or uncommon statewide. The introduction provides details on the methodology and reasoning used to develop this list. The list was started in 2001 and is updated quarterly.

Santa Barbara County Rare Plants List (compiled by Dieter Wilken)- a checklist of the rare plants of mainland Santa Barbara County, as well as four Channel Islands in Santa Barbara County (Santa Barbara, Santa Cruz, Santa Rosa, and San Miguel). This checklist was created in 2003.

Rare, Unusual, and Significant Plants of Alameda and Contra Costa Counties (by Dianne Lake) - a database that tracks the rare and unusual plants in Alameda and Contra Costa Counties. First complied in 1991, this database is updated periodically and is now in its seventh edition (2004).

Acceptability of using the Natural Heritage Program's Global/State Ranking System at the County Level (by David Magney) – a white paper examining the criteria used by the state Natural Heritage Programs and its applicability at the county level, with Ventura County used as an example.


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