The Herbarium is recognized throughout the world for its strength in documenting the diversity, distribution, variation, and ecology of more than 6500 California native plant species.
The combined Herbarium of Rancho Santa Ana Botanic Garden and Pomona College (RSA-POM) is a museum-quality collection of vascular plant specimens. With current holdings totaling over 1,200,000 specimens, the Herbarium is the tenth largest in the United States and third largest in California.

Our Holdings

The Herbarium at California Botanic Garden, the third largest in California, comprises over 1,250,000 specimens of vascular plants and a growing collection of bryophytes. The collection represents the combined holdings of the Botanic Garden’s collection [RSA] and the Pomona College Herbarium [POM]. The Herbarium’s holdings include nearly 7,000 type specimens (holotypes, isotypes, lectotypes, isolectotypes, neotypes, and isoneotypes) housed separately from the main collection. In addition to traditional herbarium sheets, the Herbarium also houses an ancillary collection of wood specimens, fluid preserved specimens, a cone and fruit collection, and nearly 100,000 anatomical and palynological microscope slides.

The Herbarium is worldwide in geographic scope, with significant holdings from the southwest U.S., Mexico, Australia, Russia, and other regions of arid, semi-arid, and Mediterranean climates. The Herbarium is one of the world’s largest repositories for specimens of vascular plants collected in California, notably southern California. Taxonomic strengths of the collection include Boraginaceae, Cactaceae, Ericaceae (Arctostaphylos), Fabaceae (Astragalus), Goodeniaceae, Lamiaceae, Phrymaceae, Poaceae, Polemoniaceae, The Herbarium is unique in that its holdings have grown substantially in a relatively short amount of time, in large part due to a number of resident botanists who made significant contributions to the Herbarium over the years. Especially noteworthy of CalBG’s botanists include Charles F. Baker, R. C. Barneby, Duncan Bell, Lyman D. Benson, Steve Boyd, Sherwin Carlquist, Ansthruther Davidson, C. Davidson, P. H. Davis, Mary DeDecker, Sarah J. De Groot, M. B. Dunkle, F. R. Fosberg, Naomi Fraga, H. S. Gentry, Verne Grant, R. Gustafson, G. B. Hinton, E. C. Jaeger, Marcus E. Jones, C. L. Lundell, Y. E. J. Mexia, Philip A. Munz, Edward Palmer, F. W. Peirson, C. G. Pringle, Peter H. Raven, J. C. Roos, Andy C. Sanders, Robert F. Thorne, Louis C. Wheeler, and Carl B. Wolf.


More than 560,000 (45%) of the >1.25 million herbarium specimens held by RSA-POM have been databased, and includes all of our California holdings as well as many specimen records in North America and worldwide. Approximately 10% of our specimens have been imaged. Records and images are available through the Consortium of California Herbaria Portal (

The holdings from Southern California exceed 250,000 and are unsurpassed by any other herbarium. In recognition of its overall strength, RSA-POM has been designated a national Research Resource Collection. Approximately 95% of the collection is composed of mounted sheets and filed according to a standardized system of classification. Ancillary collections that augment the collection include a cone & fruit collection, wood collection, fluid preserved collection, and pollen and anatomy slide collection. The RSA-POM Herbarium is an active member of the Consortium of California Herbaria.

our holdings

total holdings

Over 1,200,000 specimens

type specimens

Approximately 7,000 species

ancillary collections

cone & fruit collection (3,000 specimens); wood collection (8,000 specimens), fluid preserved collection (1,200 specimens); pollen and anatomy slide collection (approximately 100,000 slides)

systematic arrangement

Specimens in the collection are arranged by class or subclass: Psilotopsida, Lycopsida, Sphenopsida, Filicopsida, Gymnospermae, Angiospermae (Moncotyledons, “Dicotyledons”). Within each of these units families are arranged in alphabetical order.

geographic arrangement

Within each genus, the collection is organized by geographic region.


California, southwestern U.S., Mexico (with emphasis on Baja California), Australia and other arid regions

other specialties

Russia and former U.S.S.R. republics; Australasia and other Pacific regions; Cactaceae; Crossosomataceae; Goodeniaceae; Midaceae; Poaceae; Polemoniaceae; Restionaceae; Stylidiaceae; Arctostaphylos; Astragulus; Camissonia; Ceanothus; Cupressus; Iris; Ranunculus; aquatic phanerogams

total holdings

C. F. Baker, R. C. Barneby, L. Benson, S. Boyd, S. Carlquist, A. Davidson, C. Davidson, P. H. Davis, M. DeDecker, M. B. Dunkle, F. R. Fosberg, H. S. Gentry, V. Grant, R. Gustafson, G. B. Hinton, E. C. Jaeger, M. E. Jones, C. L. Lundell, Y. E. J. Mexia, P. A. Munz, E. Palmer, F. W. Peirson, C. G. Pringle, P. H. Raven, J. C. Roos, T. S. Ross, A. C. Sanders, R. F. Thorne, L. C. Wheeler, and C. B. Wolf.


More than 500,000 (~42%) of the >1.2 million herbarium specimens held by RSA-POM have been databased, which includes all of our California holdings as well as many specimen records in North America and worldwide. The majority of these specimen records are available through the RSA-POM web portal and more will become available as new records are uploaded. All California specimen records are also available through the Consortium of California web portal.

policies & protocols





for deposit





Capturing California’s Flowers: Using digital images to investigate phenological change in a biodiversity hotspot

California has the most diverse native flora of any state in the U.S., with ~7,400 terminal taxa. The state is considered a biodiversity hotspot, largely due to its high species diversity, high endemism, and major threats. Habitat destruction and fragmentation, urban sprawl, and exploitation of natural resources are among the leading threats impacting California’s native flora. Moreover, anthropogenic climate change has the potential to exacerbate these threats to an already imperiled flora. 

The digitization of herbarium specimens has advanced our knowledge of organismal response to changing conditions. However, when a digital record consists only of taxon name, date, and location, we are limited in the types of research questions that we can address. While label data can be used to address changes in species distributions, high-resolution images of herbarium specimens add a rich source of additional information regarding plant health, reproductive condition, and morphology.

The California Phenology Thematic Collections Network (CAP-TCN) is a collaborative project funded by the National Science Foundation through the Advancing Digitization of Biodiversity Collections (ADBC) program. The CAP-TCN currently includes 22 California universities, research stations, natural history collections, and botanical gardens to capture images and data of nearly 1 million herbarium specimens. This project uniquely aims to capture phenological data: information about the timing of flowering and fruiting of California’s native plant species.

In this project, the RSA Herbarium is tasked with imaging 100,000 specimens of target taxa over the first three years of the project and to database 20,000 specimens. To date, 50% and 77% of project specimens have been imaged and databased, respectively. Part of RSA’s tasks also included imaging the herbaria of Anza Borrego State Park (6,000 specimens) and California State University, San Bernardino (4,000 specimens). Imaging for both herbaria were completed in 2019.

Integral to the project are the activities that involve student participation, which forms about 90% of the workforce. The project has provided training in the form of internships for four undergraduate students from colleges and universities in Southern California. Additionally, through coordinated efforts with faculty at California Polytechnic University, Pomona (CPP), undergraduates have been barcoding specimens as a first step of the digitization process. Since the project started, more than 80 students have barcoded over12,000 specimens. More information about the Capturing California Flowers Project can be found here:

Enhancing the SoRo TCN with collections of taxonomic, geographic, and historic significance from the California Botanic Garden Herbarium

Montane regions play important roles in the diversification of continental floras and have been implicated in shaping distribution patterns and regional diversity in western North America. Species richness and high levels of endemism in montane regions, notably, the Southern Rocky Mountains, have often been ascribed to topographic complexity, edaphic diversity, and habitat heterogeneity, which contribute to population subdivision, geographic isolation, and increased opportunities for diversification The Southern Rocky Mountain Region (SoRo) supports a rich and fragile flora of diverse habitats and narrow ecological niches derived from unique geographic origins and evolutionary histories. 

The RSA Herbarium has a unique, data-rich, and curated but currently inaccessible collection of 60,700 vascular plant specimens from the SoRo region, the digitization of which tailors seamlessly with the ongoing Digitization Thematic Collections Network (TCN): Using Herbarium Data to Document Plant Niches in the High Peaks and High Plains of the Southern Rockies – Past, Present, and Future. Awarded in September 2019 by the National Science Foundation, this project will be instrumental to enhancing the TCN and enable researchers to examine contemporary patterns of distribution, identify signatures of diversification, predict future environmental change, and help to mitigate negative impacts of climate change and habitat alteration. Digitization includes 30,960 specimens especially noteworthy for their relevance to science, collector, and taxonomy. 

Graduate students at CalBG and undergraduate interns from local institutions are heavily involved in all aspects of digitization. To date, graduate students and interns have databased, imaged, and georeferenced 35%, 30%, and 10% of the total specimens in the project, respectively. More information about this project can be found here:


contact us

mare nazaire

administrative curator, rsa-pom herbarium

(909) 625-8767, ext. 268