Checklist of the Vascular Plants of San Diego County
This is the fourth edition of the Checklist of the Vascular Plants of San Diego County (here referred to as simply the "Checklist"), which catalogs all native and naturalized vascular plants known to occur in San Diego County, California, U.S.A. (Note that "naturalized" refers to non-native plants that grow, persist, and reproduce in natural, non-cultivated habitats.) This and previous editions of the Checklist (Simpson et al. 1995, 1996; Simpson and Rebman 2001) function to update A Flora of San Diego County, California (Beauchamp 1986). The need for this Checklist arose with the publication of The Jepson Manual: Higher Plants of California (Hickman 1993, here referred to as "The Jepson Manual"), which brought numerous nomenclatural changes to our County's flora. In addition, a great number of taxa new to the County have been discovered since the 2001 (third) edition and many misidentifications have been corrected.
Nomenclature for this Checklist is based on The Jepson Manual for most native plants, Hortus Third (Bailey & Bailey 1976) for some naturalized plants, or original research journal articles where pertinent (discussed below or cited in the Checklist). We have also utilized the Jepson Online Interchange for California Floristics and published volumes of the Flora of North America (Flora of North America Editorial Committee (eds.) 1993+; listed electronically at eFloras), here referred to as simply "FNA", with the appropriate volume number.
As with the third edition, this fourth edition of the Checklist provides documentation of all taxa by the listing of an accession number of a representative herbarium specimen (known as the herbarium voucher). Almost all specimen citations are from the San Diego Natural History Museum (SD), most of these from the San Diego County synoptic collection. A few specimens are cited from the herbaria at California Academy of Sciences (CAS-DS), California State University at Chico (CHCS), Rancho Santa Ana Botanic Garden (RSA-POM), San Diego State University (SDSU), University of California Irvine (IRVC), University of California Riverside (UCR), and University of California Berkeley (UC-JEPS). We feel that in preparing any floristic checklist, it is of the utmost importance that every taxon listed be documented with an herbarium specimen that is deposited and accessioned in an accredited herbarium. Without proper specimen documentation, the presence or correct identity of these taxa may be in doubt. Checklists of taxa without documentation are unverifiable and thus are out of the realm of science. We hope and encourage that future work on regional checklists and local floristic surveys, including those by governmental agencies and private consulting firms, will endeavor to provide complete specimen documentation.
Our current count of native and naturalized vascular plants documented to occur in San Diego County is 2,143 species (including hybrids), and 2,314 total taxa (including subspecies and varieties). These totals are up from the 1,996 species and 2,147 total taxa listed in our 3rd edition, mostly due to new discoveries in the interim. Thus, the documented County's flora has increased by 147 species (7.4%) and 167 total taxa (7.8%) in the four years since our 3rd edition was published. Of these additions, we have increased our knowledge of the native flora by 58 total taxa, including 40 species.
Of the 2,143 species, 1,573 (73.4%) are native to the County and 570 (26.6%) are non-native and naturalized in the County. Of the 2,314 total taxa, 1,735 (75.0%) are native and 579 (25.0%) are non-native and naturalized. These statistics illustrate the great numbers of exotic plants that have become established in native habitats, with more being detected every year.
San Diego County is often cited as having more species (or taxa) of vascular plants than any other county in the continental United States. We have to date not verified this, but we know of no other county in the continental U.S. having more species or total taxa. However, we feel that a more significant comparison between regions is the richness of native (versus non-native) plants. Thus, the 1,573 native vascular plant species or 1,735 native total taxa for San Diego County should be used in regional comparisons of natural biodiversity. Of these native taxa, 26 are endemic (rarely near-endemic) to San Diego County, further emphasizing the uniqueness of our County's flora.
The Plant Atlas Project
One of us (Jon Rebman) has been intimately involved in a concerted effort to better document plant taxa throughout the County using "parabotanists", largely volunteer botanists and amateurs who are trained to collect and document plants. This effort has led, in 2.5 years, to the addition of over 15,000 new specimens to the herbarium at the San Diego Natural History Museum (SD). Through the direct efforts of the Plant Atlas project, we have documented (at the time of publication of this Checklist: February 2006) a total of 126 new records (total taxa, including infraspecies) in the County, 33 native and 93 non-native plants. We continue to explore regions of the County that historically have been under-collected.
The excellent documentation of new collections from the Plant Atlas project will enable us to map and analyze the vascular plant diversity of the County in ways that were previously impossible. Digital scans of the voucher specimens of the San Diego County synoptic collection at SD will soon be finished, and we now have the capability of generating checklists, maps, and new additions of taxa within set grid squares. We look forward to the continued growth of the San Diego County Plant Atlas project and encourage others to become involved. Please see http://www.sdplantatlas.org for more information.
The Land Plants (also known as Embryophytes or Embryophyta) are a group of organisms that have adaptations for surviving on land and that most people equate with the term "plant". Land Plants are made up of three, relatively small groups - the liverworts, hornworts, and mosses - that lack specialized conductive tissue (xylem and phloem), plus a very large group that has conductive tissue, the Vascular Plants or Tracheophytes (see Figure 1). The basal, "non-vascular" liverworts, hornworts, and mosses (often collectively termed "bryophytes") are not treated in this Checklist because collections of these taxa are very scanty and identification of these groups requires special expertise. However, we do wish to point out the great need to document these missing elements of our flora and to ultimately expand this Checklist to include all Land Plants.
This Checklist of the native and naturalized Vascular Plants occurring in San Diego County arranges species alphabetically by plant family within major vascular plant groups. The major vascular plant groups that we recognize (based in part on Pryer et al. 2004) are: Lycophytes (=Lycopods), Equisetophytes (Equisetales, =Sphenopsids), Ophioglossoid Ferns (Ophioglossales), Leptosporangiate Ferns (Polypodiales), Conifers, Gnetales, and Angiosperms (Flowering Plants); see Figure 1, below.
These groups differ somewhat from those recognized in The Jepson Manual. For example, the traditional "ferns" (termed "Pteridophytes" in The Jepson Manual), are an unnatural, "paraphyletic" group (one consisting of a common ancestor but not including all descendents). The Lycophytes (and possibly Equisetophytes) are well-separated from other "ferns", and the Ophioglossoid Ferns (including only Ophioglossum californicum in our flora) are quite distinct from the much larger Leptosporangiate Ferns (see Figure 1).
The Seed Plants (Spermatophytes) are a major component of the Land Plants, among which only members of the Conifers, Gnetales, and Angiosperms (Flowering Plants) are native or naturalized in San Diego County (Figure 1). Interestingly, the Gnetales (including species of Ephedra in our flora) are now thought to be included within the Conifers. However, we treat them as a separate group in the Checklist.
Within the Angiosperms, we have chosen to adhere to the Angiosperm Phylogeny Group (2003) system of classification in denoting major groups and most families (see below). (Note that the Angiosperm Phylogeny Group 2003 system, commonly abbreviated "APG II" superceded the earlier Angiosperm Phylogeny Group 1998 system.) The APG II system is based primarily on molecular (mostly DNA sequence) data and the strict recognition of "monophyletic" groupings (those consisting of a common ancestor and all descendents). The native or naturalized Flowering Plants in San Diego County occur in four major taxonomic groups in the APG II system: Magnoliids (including the Calycanthaceae and Lauraceae of the order Laurales, and the Saururaceae of the order Piperales), Ceratophyllales (Ceratophyllaceae), Monocots, and Eudicots (Figure 2, below).
The traditional "Dicots" (dispersed among all the asterisked groups portrayed in Figure 2) are known with confidence to comprise an unnatural grouping, which we now formally abandon. However, of the San Diego County species that have traditionally been treated as "Dicots", almost all belong to a well defined, monophyletic group called the Eudicots. Thus, the Flowering Plants that occur in San Diego County are either Monocots, Eudicots, or one of five species in the families Calycanthaceae, Lauraceae, and Saururaceae of the Magnoliids and Ceratophyllaceae of the Ceratophyllales. These last four families are placed at the beginning of our list of Angiosperms, to denote their basal evolutionary position and their distinction from the Monocots and Eudicots. Also, note that we have now placed the Monocots before the Eudicots, to better reflect their phylogenetic sequence.
The classification of individual flowering plant families also primarily follows the APG II system. However, we have made some exceptions where warranted by more recent journal articles or where alternative and acceptable classifications better conform to traditional classification. [An excellent web site for up-to-date information on angiosperm classification and relationships is the Angiosperm Phylogeny Website (Stevens 2001 onwards).] The following are family treatments that deviate from The Jepson Manual (Hickman 1993). [Note that "sensu lato", abbreviated "s.l.", means "in the broad sense", whereas "sensu stricto", abbreviated "s.s.", means "in the strict sense".]
Lemnaceae merged into Araceae. It is clear now that the Lemnaceae are nested within the Araceae and that the former should not be treated as a separate family.
Liliaceae split. Within the Monocots, one prominent change in our Checklist (initiated in earlier editions) is the splitting of the Liliaceae, which is treated very broadly in The Jepson Manual and Jepson Online Interchange, into eleven, separate families: Agavaceae (Agave, Hesperocallis, Hesperoyucca, and Yucca), Alliaceae (Allium and Nothoscordum), Amaryllidaceae (Amaryllis and Narcissus), Asparagaceae (Asparagus), Asphodelaceae (Aloe and Asphodelus), Convallariaceae (Maianthemum), Hyacinthaceae (Chlorogalum), Liliaceae s.s. (Calochortus, Fritillaria, and Lilium only), Melanthiaceae (Veratrum and Zigadenus), Nolinaceae (Nolina), and Themidaceae (Bloomeria, Brodiaea, Dichelostemma, and Muilla). Although some of these monocot families are difficult to differentiate based on gross morphology, they do represent monophyletic groupings. Note also that Hesperocallis undulata (treated in the Hostaceae in our 3rd edition) is now placed as a member of the Agavaceae (Pires et al. 2004). In addition, Bogler et al. (2006) suggest that Chlorogalum (among others) might best be treated within an expanded Agavaceae. However, we elect to keep Chlorogalum in the Hyacinthaceae until more data are presented.
The following are changes in our Checklist regarding the classification (relative to The Jepson Manual) of Eudicot families that occur in our flora.
Adoxaceae split from Caprifoliaceae. In APG II the genus Sambucus is transferred from the family Caprifoliaceae to the Adoxaceae (as was originally done in Beauchamp 1986). The other genera in our flora that have been treated in the Caprifoliaceae (Lonicera and Symphoricarpos) remain in that family.
Apodanthaceae new to our flora. Based on recent molecular studies, the desert parasitic plant Pilostyles thurberi (parasitic on the host plant Psorothamnus emoryi) has been removed from the family Rafflesiaceae (no longer represented in our County) and classified in the family Apodanthaceae (now new to our County; see Stevens 2001 onwards). Thus, the xerophytic Pilostyles, having tiny flowers, is now thought to be quite distantly related to the tropical Rafflesia (having the largest flower in the world) of the Rafflesiaceae.
Asclepiadaceae merged into Apocynaceae. In APG II the Apocynaceae (dogbane family) have been expanded to include the Asclepiadaceae (the milkweeds), long known to be closely related to the former.
Chenopodiaceae merged into Amaranthaceae. The family Amaranthaceae is expanded in APG II to include the Chenopodiaceae, long known to be a close relative of the former. Thus, in our flora, the genera previously treated in the Chenopodiaceae - Allenrolfea, Aphanisma, Atriplex, Bassia, Beta, Chenopodium, Cycloloma, Kochia, Monolepis, Nitrophila, Salicornia, Salsola, and Suaeda - are now placed within the Amaranthaceae.
Cuscutaceae merged into Convolvulaceae. It is now clear that the Cuscutaceae, containing Cuscuta, the dodders, are nested within the Convolvulaceae, the morning glory family. The Cuscutaceae are longer treated as a separate family.
Euphorbiaceae split into three families. The Euphorbiaceae have been split by APG II into the families Euphorbiaceae, Phyllanthaceae, and Picrodendraceae. The "uniovulate" taxa (having one ovule/seed per carpel) are retained as the Euphorbiaceae. This newly delimited Euphorbiaceae family (which could be referred to as Euphorbiaceae s.s.) contains all but two species in the county among those previously placed in the family. The two "biovulate" species (having two ovules/seeds per carpel) in our County's flora are now placed in the other two families: Phyllanthus caroliniensis in the Phyllanthaceae and Tetracoccus dioicus in the Picrodendraceae.
Boraginaceae distinct from Ehretiaceae and Heliotropaceae. We follow the conclusions of Gottschling et al. (2001), which provide evidence that the Ehretiaceae (in our flora containing only Tiquilia spp.) and Heliotropaceae (in our flora containing only Heliotropium curassavicum) should be treated as families distinct from Boraginaceae.
Scrophulariaceae rearranged into several families. Recent systematic studies have produced a major re-classification of the traditional Scrophulariaceae, now known to be a highly paraphyletic group (see Olmstead et al. 2001; Oxelman et al. 2005). Based on these analyses, the traditional Scrophulariaceae (s.l.) have been reclassified into several, monophyletic units, which in our Checklist are:
Sterculiaceae merged into Malvaceae. The mallow family, Malvaceae, has been greatly expanded in the APG II system to include the Sterculiaceae.
Rejected Nomenclature Changes
We have chosen to reject some plant families that are cited in the APG II system. We base our decisions in part on the desire to retain a more traditional classification when it is an acceptable alternative and still results in monophyletic groups. In a few cases we have elected to go with recent research articles that contradict APG II. The following is a list of families that we retain.
The APG II system merges the Aceraceae into the family Sapindaceae. We elect to keep these families separate for now, although their merger is becoming widely accepted.
APG II treats the Boraginacae as s.l., including within it the families Cordiaceae, Ehretiaceae, Heliotropaceae, Hydrophyllaceae, and Lennoaceae. We follow Gottschling et al. (2001) in treating these families (the last four found in our flora) as distinct from the Boraginaceae.
The APG II system merges the Capparaceae into a Brassicaceae s.l. However, we follow the acceptable alternative of treating the Brassicaceae and Capparaceae (plus Cleomaceae, not in our flora) as separate families.
The Nolinaceae is merged with the Convallariaceae in the APG II system, but we feel that this taxonomic complex requires further study.
The genus Celtis is classified in the Cannabaceae, sensu APG II. We retain it within the Ulmaceae for now, awaiting corroborative evidence.
The Viscaceae is merged with a broadened Santalaceae (s.l.) in APG II. However, because a recent (Joshua and Nickrent 2005) study suggests otherwise, we elect to retain the Viscaceae.
This family is merged within the Potamogetonaceae, sensu APG II. We retain it for now.
We have chosen to reject some generic changes that were recognized in FNA volume 5. The FNA treatment recognized the segregate genera Fallopia and Persicaria, treated within the genus Polygonum in The Jepson Manual. We choose to follow The Jepson Manual treatment, basing our decision on a personal communication with A. Lamb-Frye (Nov. 2005) that cites recent molecular studies showing that these two segregate genera are nested within the genus Polygonum.
Generic and Species Nomenclature Changes
We have elected to make the following generic and species changes based on recent systematic studies.
Scirpus (Cyperaceae) transfers. We follow the Flora of North America vol. 23 treatment in transferring some species of the genus Scirpus to the genera Bolboschoenus (including the former Scirpus maritimus), Isolepis (including the former Scirpus cernuus), and Schoenoplectus (including the former Scirpus acutus, S. americanus, S. californicus, and S. pungens). In our flora only Scirpus microcarpus is retained in that genus.
Chenopodium (Amaranthaceae) transfers. We follow the Flora of North America vol. 4 in transferring three of our species of Chenopodium (C. ambrosioides, C. multifidum, and C. pumilio) to the genus Dysphania.
Salicornia (Amaranthaceae) transfers. We follow the Flora of North America vol. 4 in transferring Salicornia subterminalis to the genus Arthrocnemum and Salicornia virginica to the genus Sarcocornia. In our flora only Salicornia bigelovii and Salicornia depressa are retained in the genus Salicornia.
Aster (Asteraceae) transfers. We follow Nesom (1994) and Sundberg (2004) in transferring our three species of Aster into the genus Symphyotrichum.
Hymenoclea (Asteraceae) transfers. We follow the conclusions of Strother and Baldwin (2002), based in part on Miao et al. (1995), that our two species of Hymenoclea should be transferred to the genus Ambrosia.
Gnaphalium (Asteraceae) transfers. We follow Nesom (2004a) in transferring Gnaphalium purpureum to the genus Gamochaeta; another species of Gamochaeta (G. calviceps) is a recent addition to the County. We also follow Anderberg (1991) in transferring Gnaphalium bicolor to the genus Pseudognaphalium (as P. biolettii) and Nesom (2004b) in transferring the subspecies of Gnaphalium canescens to species of Pseudognaphalium.
Lessingia (Asteraceae) transfers. We follow Saroyan et al. (2000) in transferring our two varieties of Lessingia filaginifolia back to the genus Corethrogyne.
Senecio (Asteraceae) transfers. We follow Barkley (1999) in transferring Senecio ganderi to the genus Packera (as P. ganderi), and we follow the Jepson Online Interchange in transferring Senecio mikanioides to the genus Delairia (as D. odorata).
Tarweed (Asteraceae) transfers. Nomenclatural changes in the tarweed group of the Asteraceae (Baldwin 1999), which we cited in our 3rd edition, are repeated here. All of the San Diego County species previously treated in the genus Hemizonia are placed in the genera Centromadia or Deinandra. In addition, two local species of Madia are transferred to the genera Anisocarpus and Hemizonella.
Arabis (Brassicaceae) transfers. All but one of our species in the genus Arabis have now been transferred to the genus Boechera (Al-Shehbaz 2003). In our flora only Arabis glabra remains in Arabis.
Opuntia (Cactaceae) transfers. As with our 3rd edition, and following Flora of North America vol. 4, we transfer the cylindrically-stemmed species of Opuntia to the genus Cylindropuntia.
Eremocarpus (Euphorbiaceae) transfer. We follow Webster (1992) in transferring Eremocarpus setigerus to the genus Croton.
Erodium (Geraniaceae) transfer. We follow Aldasoro et al. (2002) in transferring Erodium macrophyllum to the genus California.
Mirabilis (Nyctaginaceae) transfers. As with our 3rd edition, the varieties of Mirabilis bigelovii, plus M. californica, are now all treated as varieties of Mirabilis laevis, as based on the work of Spellenberg and Rodríguez Tijerina (2001) and following Flora of North America vol. 4.
Mimulus (Phrymaceae). We follow a recent monograph of Mimulus, section Schizoplacus by Thompson (2005), which treats Mimulus aurantiacus with 6 varieties, 3 of which (var. aridus, var. pubescens, and var. puniceus) plus hybrid intermediates (var. pubescens x var. puniceus) occur in San Diego County. This treatment differs from the study of Tulig (2000), which recognized Mimulus aridus and M. puniceus as separate species.
Genera in Polemoniaceae. As with our
3rd edition, we have accepted numerous realignments in the Polemoniaceae
based on the work of Porter and Johnson (2000). In addition to
a few minor taxonomic changes involving infraspecific rearrangements
in that family, the following major changes are noted. Certain
species formerly in the genus Gilia are now placed
in the genera Aliciella, Saltugilia,
or Linanthus. The two Leptodactylon species
in our County are treated in the genus Linanthus.
Numerous species of Linanthus are transferred to
the genus Leptosiphon, and Phlox gracilis is
treated as two subspecies in the genus Microsteris.
An Alphabetical Listing of Families, citing page numbers,
immediately follows this Preface.
Appendix 1: Taxa Not Documented with Herbarium Vouchers lists taxa that have been cited in A Flora of San Diego County (Beauchamp 1986) and in previous editions of our Checklist for which no herbarium specimen voucher is known. Some of these listings may be mistakes from past treatments or anecdotal checklists; known misidentifications are indicated in this list with "?". Others may well occur in our County, but are either not documented (with a voucher herbarium specimen) or are documented in an herbarium without our knowledge. Some may have occurred in the County in the past but are now extinct and without a voucher. A few of the taxa found in this list are based on database reports provided by John Kartesz, but are most likely misidentifications of specimens at other herbaria. We hope to clarify many of these undocumented taxa in the future. However, we hold the view that listed taxa for which there is no evidence (i.e., no herbarium specimen voucher) cannot be accepted as occurring in San Diego County.
An Index of Genera and Families at the back of the Checklist may be used to quickly locate a taxon listing.
Notes near the end of the Checklist may be used for personal recording of data.
Environmental listing information is based on California Native Plant Society. 2001. Inventory of Rare and Endangered Plants of California (6th edition; Rare Plant Scientific Advisory Committee, David P. Tibor, Convening Editor.) and on California Department of Fish and Game. July 2000. Natural Diversity Database (Special Plants List. Biannual publication, Mimeo. 136 pp.). The number and letter code from the CNPS Inventory and symbols from the Natural Diversity Database are explained on the inside back cover of the printed Checklist. In cases where the CNPS Inventory cites a taxon not recognized in The Jepson Manual, the CNPS Inventory name is treated here as a synonym, with environmental listing for that synonym included.
We thank Duffie Clemons (posthumously) and Jerilyn Hirshberg for noting or discovering numerous additions to our County's flora in the Cuyamaca and Laguna Mountains (see Hirshberg and Clemons 1996). We thank Robert Lauri for discovering several new County records in the Palomar Mountains (Lauri 2004) and for contributing the cover image of Lilium parryi. We thank Craig Reiser (posthumously) for past documentation of several additions to the County. We thank Steve Boyd and Andy Sanders for providing documentation of some species in the herbaria at Rancho Santa Ana Botanic Garden (RSA-POM) and University of California Riverside (UCR), respectively. We thank Tom Chester and John Kartesz for new County verifications and for pointing out discrepancies between our Checklist and other databases, and we thank Tom Chester and Fred Roberts for numerous editorial comments on this edition. We thank Daniel Simon for researching FNA volumes for nomenclatural changes in our County records and MaryAnn Brooks-Gonyer for supplying missing common names of many documented plants. We thank Phil Unitt for allowing us to use the cover map of San Diego County vegetation (based on those compiled by the U.S. Forest Service, Anza-Borrego Desert State Park, and the San Diego Association of Governments). We thank Jeannie Gregory, Mary Ann Hawke, Marty Jacobson, John Sanborn, and numerous volunteers at the San Diego Natural History Museum Herbarium (SD) for their help in processing and recording vouchers. We thank all of the parabotanists of the Plant Atlas Project who have contributed their time and efforts in collecting plant specimens throughout San Diego County. A special thanks to Karen Rich for helping us to finish off the numerous, small details needed to finish this new edition. Finally, we thank Scott McMillan, Brenda McMillan (formerly Brenda Stone), and Judy Gibson for their contributions to earlier editions of this Checklist.
We would appreciate and encourage notification of any vouchered additions or corrections to this Checklist, particularly knowledge of voucher specimens or field localities of taxa for which we lack documentation (in Appendix 1). Please relay such information to Dr. Jon Rebman, San Diego Natural History Museum, P.O. Box 121390, San Diego, CA 92112-1390 (SD Herbarium: 619-255-0229; email: email@example.com) or to Dr. Michael Simpson, Dept. of Biology, San Diego State University, San Diego, CA 92182-4614 (SDSU Herbarium: 619-594-4479; email: firstname.lastname@example.org).
NOTE: Online access, including additions, corrections, and other listings of the Checklist, will be available in the future from the web page: http://www.sdnhm.org/research/botany