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Michael Wall, Ph.D.
Director of the Biodiversity Research Center of the Californias

Photo: Mary Ann Hawke

San Diego County Plant Atlas

By Mary Ann Hawke, Ph.D., Project Director

San Diego County is the most botanically diverse county in the contiguous U.S. and as such is identified as an international "hotspot" of biodiversity. Being in one of only five regions of the world with a Mediterranean climate, it spans a wide range of habitats from the coast to the mountains to the desert. From surf-grass to cactus, the county boasts a total of 2143 plant species (1573 native and 570 non-native). Twenty-six are endemic to San Diego County (growing only within the county habitats from the coast to the mountains to the desert. From surf-grass to cactus, the county boasts a total of 2143 plant species (1573 native and 570 non-native). Twenty-six are endemic to San Diego County (growing only within the county borders) and a dozen plants are listed as federally endangered.

Five years ago, Curator of Botany Dr. Jon Rebman called for the creation of a regional plant atlas project because our knowledge of the flora of San Diego County was surprisingly limited. Only one quarter of the specimens in the Museum's existing plant collection came from locations within the county, and the published flora was outdated. There were few books, no centralized source of information about the county's flora, and little interaction between local botanical experts and environmental professionals.

The San Diego County Plant Atlas project started in 2002, when Museum staff met with a group of interested biologists and land managers to discuss the need to build on existing botanical collections and study the county's flora in a more coordinated and comprehensive manner. The Museum's San Diego County Bird Atlas project, which successfully involved hundreds of volunteer field workers, served as a model. Soon the Botany Department began recruiting and training interested volunteers (called "parabotanists") to systematically collect plant specimens within the same county-wide grid system used for the birds.

To date, over 540 parabotanists have been trained and an online data entry system and searchable database have been developed. The public website ( allows visitors to view plant photos, read the project newsletters, map the locations of species, and generate floristic checklists for particular areas. Despite less-than-ideal collecting conditions caused by the past few years of drought, over 28,000 new specimens have been submitted, including 126 new county records. This translates into a 7.8% increase in the county's documented flora, by adding 167 taxa to the most recent edition of the Checklist of Vascular Plants of San Diego County, by Jon P. Rebman, Ph.D., and Michael G. Simpson, Ph.D.

Despite this significant progress, much is still not known, even as our natural habitats are being altered by fire, drought, invasive species, and urban growth, or are threatened by global climate change. After four years, the Plant Atlas project is estimated to be about one-third completed. The long-term goal—to collect one representative specimen of each native or naturalized plant species that grows in each atlas grid square—is projected to add over 100,000 specimens to the existing collection.

Why the focus on collecting specimens? For over 130 years, the Museum has been a leader in the preservation and interpretation of scientific specimens (more than eight million, dating back from 1874 and on). Dried and pressed plant specimens can last for hundreds of years, preserving physical samples of plant diversity for use in scientific research and education. Imagine visiting our "plant library" (called an herbarium) where you could select a specimen collected over 130 years ago, examine it under a microscope, compare it to a modern collection, or take a DNA sample for genetic analysis.

Only 5% of natural history collections data worldwide are computerized, but the Museum's historic plant collections are now entirely databased, thanks to a federal grant provided by the Institute of Museum and Library Services. That grant is also allowing us to increase the value of the collections by adding or improving the quality of geospatial information ("georeferencing") and making the data and mapping tools available online so that the information is more accessible and useful to the public, researchers, and land managers.

Combining historic records with the new Plant Atlas collections, we now have over 60,000 data points (each one a vouchered specimen) available to help analyze changes in our county's plants across time. A project just funded by The San Diego Foundation will examine these data for trends that may be occurring due to climate change. For example, have there been changes in the flowering times of any local species that might disrupt the synchrony with insect pollinators, or migrating birds? On which plant species should we focus future monitoring? As the Plant Atlas moves forward, the new plant collections will serve as the baseline against which to compare changes in our plant life due to future environmental and climatic conditions.

San Diego County contains a rich heritage of botanical diversity and we have an obligation to better understand and preserve it for ourselves and for future generations. By involving the public as "citizen scientists," the San Diego County Plant Atlas project continues to build bridges between average citizens and the scientific and natural worlds.

Learn more about the Plant Atlas project at The two-year federal grants that partially funded the Plant Atlas (from the National Science Foundation and the IMLS) are ending soon, so to keep the project going the Museum is looking for funding opportunities from foundations, research organizations, and local contributors.To find out how you can help, email or call 619.255.0298.

Parabotanist Victoria Marshall prepares plant specimen.
Photo by Jeannie Gregory