top of page


Jon P. Rebman, Curator of Botany at the San Diego Natural History Museum, has organized symposia and research trips, written excellent articles and given thoughtful lectures about native plants. He demonstrates the great leadership on the tremendously important San Diego Plant Atlas Project, and has helped bring a deeper understanding of the plants in our region. His invaluable contributions to botany are impressive and urgently needed.


Jon P. Rebman, Ph.D., was born and raised in Rushville, Illinois. Being from the land of corn and beans, he can remember his fascination with the bizarre forms and shapes of cacti and succulents at a very early age and would even grow them on his window sill. However, he did not really pursue a botanical degree until he was an undergraduate at Millikin University, where a couple of really good biology/botany professors sparked his interests and academic curiosities about plants. Subsequently, he earned a Masters degree at Southwest Missouri State University, working on floristics of a natural area in the Ozarks region; and then a Doctoral degree at Arizona State University, focusing on the taxonomy of cholla cacti in Baja California. While pursuing his doctorate Jon was very lucky to obtain a Fulbright/Robles Fellowship to Mexico, and he spent a year at the Universidad Autónoma de Baja California in Ensenada doing research and completing field work in the region for his degree. This amazing professional and cultural opportunity in Mexico spurred on his interests in the entire flora of the Baja California/Southern California region, and he is still specializing in this region’s flora at present. He also enjoys gardening as a hobby, and has recently converted his entire front yard into a succulent xeriscape.

Since 1996 Jon has been the Mary and Dallas Clark Endowed Chair/Curator of Botany at the San Diego Natural History Museum (SDNHM). Dr. Rebman is a plant taxonomist and conducts extensive floristic research in Baja California and in San Diego and Imperial Counties. He leads various field classes and botanical expeditions each year and is actively naming new plant species from our region. His primary research interests have centered on the systematics of the Cactus family in Baja California, especially the genera Cylindropuntia (chollas) and Opuntia (prickly-pears). Rebman also does a lot of general floristic research, and he co-published the most recent edition of the Checklist of the Vascular Plants of San Diego County.

He has over 22 years of field experience with surveying and documenting plants including rare and endangered species. As a field botanist, he is a very active collector of scientific specimens with his personal collections numbering over 22,400. Since 1996 he has been providing plant specimen identification/verification for various biological consulting companies on contracts dealing with plant inventory projects and environmental assessments throughout southern California.

Rebman is the director of the San Diego County Plant Atlas project and identifies/verifies all of the new specimens (currently over 54,000) coming into the herbarium through this scientific endeavor. As the curator of the SD Herbarium at the SDNHM, he is in charge of this dried plant specimen collection that contains over 210,000 specimens dating back to the 1870s. Dr. Rebman is in the process of finishing a book entitled Ferns and Lycophytes of San Diego County, co-authored with Annette Winner. This local natural history publication should be available early next year (2012). It contains detailed information on 60 different ferns and lycophytes from our region. Rebman also just finished a new edition of the Baja California Plant Field Guide, with co-author Norman Roberts, due out in December 2011, and is working on a new specimen-based checklist for the plants of Baja California.

San Diego County Plant Atlas Project

One of the regional floristic research projects that has been consuming much of Rebman’s time in the last few years is the San Diego County Plant Atlas project, of which he is the director. This multi-year project is designed to improve scientific knowledge of regional plants through better documentation of the flora of San Diego County by using volunteers from the community (called parabotanists) to properly survey, collect herbarium-quality voucher specimens, and record field data about plants in natural areas throughout the County. Since its inception in August 2003, the project has developed a comprehensive website ( to assist parabotanists and provide an outlet to the public, and designed an efficient system for online data submission and delivery of specimens to the SDNHM.

It has already added over 54,500 new voucher specimens to the SD Herbarium (including more than 350 discoveries of new county records and two new taxa for science), that are fully databased (with precise geographic coordinates), created online floristic search processes and resources for mapping plant distributions, and trained over 600 volunteers. Consequently, this project is fostering the public’s awareness and respect for local natural history, increasing our scientific collections of the regional flora, and providing essential botanical data on the distribution, variation, and diversity of the plants found in our County.

Even though the Plant Atlas project is not yet complete, it has still produced very important results that have altered our understanding about our regional flora. In respect to diversity, the Plant Atlas has increased our knowledge by adding many new native and non-native plant records (more than 350) to the County. Consequently, San Diego County is considered to be one of the most botanically diverse counties in the U.S., with more than 2500 different native and naturalized plants present. New county records been added, and at least two new plants for science have been discovered.

One of the new plant discoveries was collected by Dr. Rebman on Viejas Mountain near Alpine during field surveys for that particular atlas grid square. This new entity was studied by botanists and technically described for science and named in honor of Rebman. The new fern (in the family Pteridaceae) occurs only in south-central San Diego County and extreme northwestern Baja California, and is called Rebman’s Silverback Fern (Pentagramma triangularis subsp. rebmanii).

With the continuing documentation of plant populations in the County through the Plant Atlas, some new distributional trends and concepts about our flora are also emerging. For example, we are starting to observe a consistent trend in various Sonoran desert plants found in Anza-Borrego Desert State Park (on the eastern edge of our county) that also occur in the extreme southwestern part of our county near the Pacific Ocean, but do not have any populations in between. This discovery may result in the need for more detailed studies on the biogeography of some desert species that could have arrived in southwestern San Diego County via an historical desert corridor that occurred between mountain ranges in northern Baja California.

As part of the Plant Atlas project and its influence on significantly increasing popular interest in local plants, SDNHM has developed an online searchable photographic archive of digital plant photos from San Diego and Imperial Counties. This web-based resource is accessible through the Plant Atlas website ( At present, this photographic database contains more than 11,500 digital plant images from Southern California (mostly San Diego County) that are available online; it is growing each week with additional georeferenced, digital field photos following botanical field outings. Many of the plant photos in this online collection are especially valuable because they are directly linked to herbarium specimens and are cross-referenced to reliable locality/field data. Our hope is that this resource will become an essential utility for educating the public and will directly connect to the distributional data that is being accumulated by the Plant Atlas project.

The Plants of Baja California and Floristic Research

The Baja California peninsula is a narrow strip of land stretching approximately 800 miles long and ranging from 28 miles to 149 miles wide. Its geographic position, latitudinal span, and topographic heterogeneity have conferred a diverse assemblage of weather regimes including a Mediterranean-type, winter rainfall climate; extreme arid, hot desert conditions; and tropical, summer rainfall patterns. In addition, the region's biogeographic history and physiognomy have resulted in a wide range of vegetation types that include coastal sage scrub, chaparral, oak woodland, conifer forest, many desert scrub types, and tropical deciduous forest. The peninsula is also characterized by the presence of several islands varying in distance (<0.6 miles to 149 miles) from its coast, which are located in the Gulf of California (Sea of Cortés) and the Pacific Ocean.

This piece of land and its adjacent islands support a wealth of species diversity in many different plant families. It is estimated that the flora consists of more than 4,000 plant taxa with approximately 30% of these known only from (endemic to) the Baja California region. Many of the plants from the peninsula and its islands are unique and stretch the imagination in respect to plant form and structure undefined including the bizarre Boojum Tree/Cirio (Fouquieria columnaris), the giant Elephant Cactus/Cardón (Pachycereus pringlei), and elephant trees (Pachycormus discolor and Bursera spp.).

Unfortunately, the rich diversity of plants that comprise the Baja California flora faces many threats such as habitat loss and degradation to pressure from competition with invasive plant species, fire, plant disease, drought, and pests. Some parts of the region such as the northwestern, coastal portion of the peninsula are experiencing extremely rapid urban development and habitat loss is reaching a critical level. Due to a lack of botanical study and inaccessible documentation (specimens of populations not yet databased or generally known, or the lack of collections of invasive plant species) we are not able to accurately assess many of these threats. Adding to the problem, the published Flora of Baja California is more than 30 years old, lacks at least 800 plant taxa, and provides only limited distribution information.

As a result of these combined factors, there is an urgent need to increase our knowledge of the botanical resources in Baja California. Regional scientists, land managers, and conservation-oriented organizations currently have limited scientific data on the local flora, along with mounting responsibilities for preservation and informed decision-making that will affect the future of the region’s biodiversity.

Current collections-based curatorial and research projects being conducted by the SDNHM under the guidance of Jon Rebman, such as the Baja California vascular plant checklist project, data entry and georeferencing of specimens deposited in the SD Herbarium, and the digitization of plant photographic slides and prints in the Museum’s botanical archives, are providing many online resources for the public, conservation, and scientific communities. To date, more than 4200 specimen vouchers (one of each taxon to be used as a visual resource for identification in a virtual herbarium) that document the diversity of the flora of Baja California (BC) and Baja California Sur (BCS) have been scanned; approximately 24,000 digitized plant and landscape photographs primarily from the Baja California region, and many other web-based botanical resources are available online at These ongoing projects along with the increased accessibility to the SD Herbarium specimen data (approximately 43,000 records from the Baja California region in electronic format) and the development of the Baja California Botanical Consortium (BCBC), which is a combined dataset that contains 72,000 specimen records from five regional herbaria in CA, BC, and BCS, will provide an indispensable tool for mapping, conserving, and better understanding diversity and distribution trends of the flora of Baja California. These botanical resources will help to produce the most comprehensive, scientifically sound, information possible on the plants of Baja California.

Dr. Rebman has been conducting botanical research and publishing new plant species in Baja California for more than 20 years. New plant species that Rebman has previously described for science include: Ambrosia humi, Grusonia robertsii, Amyris carterae, Cylindropuntia delgadilloana, Cylindropuntia sanfelipensis, and Cylindropuntia lindsayi. Rebman’s publications on the flora of Baja California are listed on our website.

Plant Systematics/Taxonomic Research

Naming and describing new species for science is an essential part of understanding our biodiversity and conserving it for the future. As a result of many years of extensive field work, plant collecting, plus lab and herbarium research on the flora of southern California and Baja California, Dr. Rebman, has discovered approximately 15 new plants from our region that still need to be formally described in order to be recognized by the scientific and conservation communities. Some of these new plant species already have ample collections available in order to describe them right now, and require only the time to study and write them up in a publication and have a botanical illustration drawn, but others will require return visits to the region where they grow in order to obtain better specimen samples and an increased understanding of their local environment and associations.

In the next few years, one of Rebman’s scientific goals will be to formally describe and publish many of these new plant species for science. By publishing these new plants the scientific community will become aware of them and this will lead to a better overall understanding of the taxonomy, diversity, and biogeography of plants in our region. Most of these plants are also very rare and by formally publishing them the conservation community will also become aware of their presence and this may help to protect and manage biological resources in our region. All of these newly described plants will add to the impressive diversity and endemism of the flora of southern California and Baja California.

Continued taxonomic investigation on cacti will soon yield the publication of Rebman’s doctoral and post-doctoral research on the chollas (Cylindropuntia spp.) of Baja California. The methods used in this biosystematic work include: chromosome studies, pollen stainability, scanning electron microscopy of pollen, seed surfaces, and certain vegetative structures, field and herbarium analyses of morphology, and biogeographical data mapping. This study represents the first comprehensive monograph of this cactus group in Baja California. The Baja California peninsula and its adjacent Pacific and Gulf islands are found to contain 27 cholla taxa, making it the area of highest taxonomic diversity of the genus Cylindropuntia. Of these taxa, 17 or 63% are endemic to the region. This systematic treatment recognizes four new taxa (Cylindropuntia alcahes var. gigantensis, C. alcahes var. mcgillii, C. cedrosensis, and C. ganderi var. catavinensis) and three previously described species by the author (C. delgadilloana, C. lindsayi, and C. sanfelipensis); six new nomenclatural recombinations; and 12 new nomenclatural types.

Baja California has 18 cholla species, of which nine are endemic. This high diversity of chollas most likely reflects the influence of past geological events and habitat diversity as well as past and present floristic associations. Chromosome studies of the chollas in Baja California indicate that most taxa (67%) are diploid, but some occasionally have putative autopolyploid individuals. If these autopolyploid taxa are considered, then up to 52% of the taxa have all or some members with polyploid counts. The range of euploidy varies from 2x to 8x (x = 11), with the octoploids reported as the highest polyploid level determined for the genus Cylindropuntia. Chromosome counts for 12 taxa in the region are reported for the first time. Hybridization is a common occurrence in the Cactaceae, especially in the subfamily Opuntioideae. The chollas of Baja California are no exception with naturally occurring putative interspecific hybrids arising from such parents as C. alcahes, C. bigelovii, C. californica, C. cholla, C. ganderi, C. molesta, C. prolifera, and C. tesajo. The publication of this taxonomic research will be an important step towards better understanding the amazing diversity and evolution of cacti in Baja California.

Literature Cited:

  • Bullock, S., J. M. Salazar Ceseña, J. Rebman, and H. Riemann. 2008. Flora and vegetation of an isolated mountain range in the desert of Baja California. The Southwestern Naturalist 53: 61-73.

  • Garcillán, P. P., J. Rebman, and F. Casillas. 2009. Analysis of the non-native flora of Ensenada, a fast growing city in northwestern Baja California. Urban Ecosystems, DOI 10.1007/s11252-009-0091-1.

  • León de la Luz, J., and J. Rebman. 2010. A new Ambrosia (Asteraceae) from the Baja California Peninsula, Mexico. Bol. Soc. Bot. Mex. 86: 65-70.

  • León de la Luz, J., J. Rebman, M. Domínguez-León, and R. Domínguez-Cadena. 2008. The vascular flora and floristic relationships of the Sierra de La Giganta in Baja California Sur, Mexico. Revista Mexicana de Biodiversidad 79: 29-65.

  • León de la Luz, J. L. and J. Rebman. 2002. The vascular flora of Cerralvo Island. Appendix 4.2, pp.512-526 in A New Island Biogeography of the Sea of Cortés, Oxford University Press, New York.

  • Rebman, J. 2006. A new club cholla, Grusonia robertsii (Cactaceae) from Baja California Sur, Mexico. Madrono 53: 280-283.

  • Rebman, J., and F. Chiang. 2005. A new species of Amyris (Rutaceae) from Baja California Sur, Mexico. Novon 15: 350-353.

  • Rebman, J., T. Oberbauer, and J. Luis León de la Luz. 2005. La flora de Isla Guadalupe y sus islotes adyacentes. Chapter, pp.67-81 in Isla Guadalupe: Restauración y Conservación, Instituto Nacional de Ecología (INE-SEMARNAT), México D.F.

  • Rebman, J. 2002. Plants endemic to the Gulf islands. Appendix 4.5, pp. 540-544 in A New Island Biogeography of the Sea of Cortés, Oxford University Press, New York.

  • Rebman, J., T. Oberbauer, and J. L. León de la Luz. 2002a. The flora of Toro Islet and notes on Guadalupe Island, Baja California, Mexico. Madroño 49: 145-149.

  • Rebman, J., J. Luis Leon de la Luz, and R. Moran. 2002b. Vascular plants of the Gulf islands. Appendix 4.1, pp.465-511 in A New Island Biogeography of the Sea of Cortés, Oxford University Press, New York.

  • Rebman, J. 2001. Succulent diversity in Lower California Mexico. Cactus and Succulent Journal (US) 73: 131-138.

  • Rebman, J. and D. Pinkava. 2001. Cylindropuntia delgadilloana, a new cholla (Cactaceae) from Baja California, Mexico. Journ. Ariz.-Nev. Acad. Sciences. 33: 154-156.

  • Rebman, J., M. Resendiz & J. Delgadillo. 1999. Diversidad y documentación de las Cactaceae de Baja California, Mexico. Cactaceás y Suculentas Mexicanas 44(1): 20-26.

  • Rebman, J. 1999. A new cholla (Cactaceae) from Baja California, Mexico. Haseltonia 6: 17-21.

  • Rebman, J. 1997. Opuntia lindsayi, a new cholla (Cactaceae: Opuntia, subgenus Cylindropuntia) from Lower California, Mexico. Cactus & Succulent Journal (U.S.) 69(2): 67-70.

  • Wiggins, I. 1980. Flora of Baja California. Stanford University Press. 1025pp.

bottom of page