California Flora Research Articles

The Search for the Perfect Color: Pigments, Tints, and Binders in the Scientific Expeditions to the Americas

In the eighteenth century, the Spanish Crown underwrote several expeditions in order to collect, classify, and describe the newly available natural resources in the Americas. In an attempt to convey scientific information objectively, expedition artists had to depict their specimens with absolute fidelity. Because many of them had not mastered the techniques necessary for botanical illustration, despite their formal training, Jose Celestino Mutis created a school for local artists in the New Kingdom of Granada (present day Colombia). Pigments and dyes that artists could not obtain from Spain or from the major cities in the New World through which they passed were often derived from experimentation with local materials.

Endemic Pyropia species (Bangiales, Rhodophyta) from the Gulf of California, Mexico

The evaluation of geographic distribution of Pyropia along the Gulf of California, Mexico, was realized using molecular data from two loci, the plastid rbcL gene and the partial 18S ribosomal DNA (rDNA), in conjunction with morphological observations. Dawson described two endemic species for the genus Pyropia (Pyropia hollenbergii and Pyropia pendula) in the Gulf of California based on taxonomic characteristics. In this study, we collected 130 samples from 13 locations from February 1998 to April 2008. Samples showed similar morphologies and growth habits and share a very similar type descriptions and habitat records. Using morphological and anatomical characteristics, we identify individuals as P. hollenbergii and P. pendula. However, using the molecular data, we identified five identities, which we have classified as P. hollenbergii, P. pendula, Pyropia sp. Gulf of California I (GCI), Pyropia sp. GCII, and Pyropia sp. GCIII. Phylogenetic trees based on partial 18S rDNA and rbcL sequence data showed a deep division in the genus that is not obviously correlated with existing morphological characteristics and indicate that representatives of the Gulf of California flora have undergone long reproductive isolation.

Island Specialists: Shared Flora of the Alta and Baja California Pacific Islands

The floristic connection between the mediterranean region of Baja California and the Pacific islands of Alta and Baja California provides insight into the history and origin of the California Floristic Province. We present updated species lists for all California Floristic Province islands and demonstrate the disjunct distributions of 26 taxa between the Baja California and the California Channel Islands. These 26 plant taxa are found among the 16 Pacific islands without occurring on the intervening mainland of Alta California. Separate species lists for each island group (8 California Channel Islands and 8 Baja California Islands) were compiled. These lists were compared to the mainland California flora to identify species that occur on the California Islands and either the Baja California Pacific Islands or the mediterranean region of the Baja California Peninsula, but not the mainland of Alta California. This first compilation of the flora of the Baja California Islands and nomenclatural updates for the Channel Islands provide a platform for future research and conservation planning.

Climatic niche shifts in the serpentine soil flora of California

Question Soil properties are known to have a profound effect on the geographic distribution of plants. Unusual soils seem to allow species to occur outside their ‘typical’ (realized) climatic niche. However, the generality of this pattern, and the mechanisms that drive it, are poorly known. Here, we focus on the tendency for some plant species to occur at unusually low elevations on infertile substrates, especially serpentine soils. We ask whether there is a flora-wide trend in the state of California toward lower elevations and warmer thermal limits on infertile serpentine soils than on other soils. Location State of California, USA. Methods We used herbarium data from 19 institutions. We only used species collected from both serpentine and non-serpentine soils. To focus on plant response to recent climate, we discarded records from before 1979. Finally, we discarded records that did not report latitude and longitude. The final data set consisted of 36 045 specimens representing 814 species. Latitude and longitude were used to infer elevation, temperature and soil type. We then developed a simulation modelling approach to test for significant differences in elevational and thermal distribution between serpentine and non-serpentine soils. Results Serpentine populations are found at lower elevations than non-serpentine populations, at both the low and high ends of elevation distributions (two tailed t-test, P < 0.01). This pattern is partially matched by temperature: both high and low temperature data indicate that serpentine populations are limited to less extreme temperatures than non-serpentine populations (two tailed t-test, P < 0.01). Conclusions We show that there is a flora-wide trend toward lower elevation limits on serpentine soils in the state of California. Temperature data suggest a slightly different pattern, with serpentine plants occupying more moderate temperatures. We suggest that this difference may be due to a decoupling of elevation and temperature in some parts of California. Overall, our results are consistent with two mechanisms of plant range limitation: (1) a biotic mechanism at lower elevations (high temperatures), where serpentine provides a refuge from competition; and (2) an abiotic limit at upper elevations (low temperatures), where the effect of cold is exacerbated by the infertility of serpentine.

Sanicula Deserticola, an Endemic of Baja California

One of the more restricted species of northern Baja California is Sanicula deserticola Bell, known from a few disjunct populations at the northern margin of the Sonoran Desert. One population is known from near El Marmol at the headwaters of the Arroyo de San Fernando, while others are in the yellow hills northwest of Rancho Arenoso and near Rancho Aguajito, both in the drainage of the Arroyo del Rosario. At the lastmentioned locality, it was found growing abundantly on the northwestfacing slopes of a yellow conglomerate hill, 3.6 miles west of Rancho Aguajito (Raven, Mathias , and Turner 12,678 ), associated with Rosa minuti f olia, Euphorbia misera , Yucca whipplei eremica, Idria columnaris, Eriogonum jasciculatum, E. scalare, Encelia с ali fornica var. as peri f olia, Calandrinia maritima, H ar j or dia macroptera, Brodiaea pulchella, Layia platyglossa, and Filago calijornica , as well as two species of Agave and one each of Dudley a, Mammillaria, Echino с er eus, Echino cactus, and Opuntia. This curious mixture of characteristic members of the California flora and such species as Idria columnaris, restricted to the Sonoran Desert, clearly demonstrates the unique ecological position of Sanicula deserticola. The subfamily Saniculoideae of the Umbelliferae, with some 260 species, like the other subfamilies Hydrocotyloideae and Apioideae, has apparently had a long and independent evolutionary history. The distribution of the extant genera of Saniculoideae shows clearly that they have developed within the Arcto-Tertiary Geoflora and have been associated with it for a long time, perhaps since late Mesozoic time when this Geoflora is first recognized in the fossil record. Several of the genera in this subfamily are restricted to areas of Arcto-Tertiary-derived deciduous forest in eastern Asia. Others range south along mountain chains to Africa. The genus Eryngium is world-wide in distribution, whereas the genus Sanicula is exceedingly widespread in the Northern Hemisphere, with some of its species occurring also in the Southern Hemisphere. Shan and Constance (1951) considered the section Sanicula ( Sanicla ), with about one-third of the species of the genus Sanicula , the main trunk of the genus. Some species of this section are widespread in Eurasia, and their present distribution suggests development of the section from a northern stock with subsequent southerly migrations. In North America S. mari landica L. and S. tri j oliata Bickn., which Shan and Constance considered probably the least advanced species, occur as common associates of the eastern deciduous forests. The distribution of this section is therefore

The Origin and Phylogenetic Relationships of the Californian Chaparral ‘Paleoendemic’ &lt;I&gt;Pickeringia&lt;/I&gt; (Leguminosae)

Abstract Pickeringia, a monotypic genus of the Leguminosae endemic to the xerophytic sclerophyllous chaparral vegetation of the California Floristic Province, has been considered a “relict” of legume diversity in the North American flora and an example of the classic “paleoendemics” in the flora of California. Evidence is presented for the phylogenetic relationships of this genus, inferred from nucleotide sequence variation in the internal transcribed spacers of nuclear ribosomal DNA and the plastid matK gene. Phylogenies derived from maximum parsimony and Bayesian analyses both strongly support a close relationship of Pickeringia to the temperate to subtropical, deciduous genera Cladrastis and Styphnolobium of tribe Sophoreae consistent with morphological and cytogenetic evidence rather than to members of tribe Thermopsideae where the genus has been treated taxonomically. Cladrastis is resolved as paraphyletic while Styphnolobium is strongly supported as a monophyletic group. These results, plus an estim...

Ecological variation in leaf biomechanics and its scaling with tissue structure across three mediterranean‐climate plant communities

Summary The mechanical resistance of leaves has key ecological implications but its basis has not been well understood, particularly at the tissue scale. We tested the hypotheses that leaf mechanical resistance should be a function of tissue density, increasing from the lamina to the midrib, and higher in drought‐tolerant than drought‐avoiding species. In a common garden study, we quantified nine leaf biomechanical traits, including measurements of material and structural resistance, and in addition 17 morphological traits, at the tissue and whole‐leaf scales, for 21 species from three semi‐arid communities of California, USA. The mechanical properties of leaves depended strongly on tissue density. Material resistance was significantly greater in the midrib than in the leaf lamina, and tissue resistances were significantly correlated among tissues, lower in deciduous coastal sage species and higher in evergreen drought‐tolerant chaparral species. The proportion of the biomass invested in the midrib was lower in species bearing midribs and laminas of high material resistance. Our results support the hypothesis of a hierarchical partitioning of leaf mechanical resistance among leaf tissues reflecting the investment of dry mass. Also, our data indicated a mechanical compensation in leaf design, where leaves with high material resistance and density deploy a relatively minor proportion of support tissue in the midrib. Finally, our results establish a quantitative basis for differences among communities in leaf biomechanics. Our results supported the classical characterization of the mediterranean‐climate flora of California according to the dramatic increase in the mean leaf mechanical resistance from species of coastal sage to chaparral, with diverse leaf types in the Mojave Desert species.

Investigation of the importance of rock chemistry for saxicolous lichen communities of the New Idria serpentinite mass, San Benito County, California, USA

AbstractAlthough several lichen inventories exist for European ultramafic sites, only four surveys of serpentine lichens for North America have been published to date. Of those, only one has been conducted in California. We conducted a survey of saxicolous lichens from ultramafic rocks (including nephrite, partially serpentinized peridotite, and serpentinite) and non-ultramafic rocks (including silica-carbonate, shale, and sandstone) at the New Idria serpentinite mass, San Benito County, California. X-ray Fluorescence Analysis of the rocks from which the lichens were collected revealed significant elemental differences between the ultramafic and non-ultramafic rocks for 26 of the 32 major and trace elements analyzed. We identified a total of 119 species of lichenized and lichenicolous fungi; 60 species were restricted to ultramafic substrata, 19 to silica-carbonate, and 15 to shale and sandstone. Only 4 species were shared in common. A permutational multivariate analysis of variance (perMANOVA) test revealed significant differences in lichen assemblages between ultramafic and non-ultramafic rocks at the species level but not at the generic level, with species richness (alpha-diversity) significantly greater at the ultramafic sites. We suggest that, although differences in geochemistry clearly influence the lichen community composition, other factors, especially substratum age and the physical characteristics of the rock, are of equal, if not greater, importance. Of all the species collected, six,Buellia aethalea,B. ocellata,Caloplaca oblongula,Rhizocarpon saurinum,Thelocarpon laureri, andTrapelia obtegens, are reported new to California, along with an apparently previously undescribedSolenopsorasp. The rest of the species encountered are relatively frequent in the lichen flora of southern and central California, exceptAspicilia praecrenata, a rare California endemic that we collected on both ultramafic and non-ultramafic rocks.

Why Are Trade-Offs between Flower Size and Number Infrequently Detected? A Test of Three Hypotheses

Although the flower is the unit of sexual reproduction in angiosperms, a plant’s reproductive success is determined by its entire floral display. A trade-off between the size and number of flowers produced is an assumption of models of floral display evolution, but this trade-off is often not observed. We tested three hypotheses for why a trade-off between flower size and number is not observed, using 32 populations of Mimulus guttatus and 83 genera from the California flora. We found support for the hypothesis that high variance in resource acquisition masks a trade-off between flower size and number. In contrast, we did not find support for the hypothesis that trade-offs between current and future reproduction mask negative correlations between flower size and number in lineages with a perennial life history. We also did not find support for the hypothesis that negative flower size-number correlations are less likely to be observed in lineages with lower variation in flower number because the correlatio...

Can a breakdown in competition–colonization tradeoffs help explain the success of exotic species in the California flora?

Determining combinations of functional traits that allow a species to colonize new habitats has been central in the development of invasion ecology. Species able to establish in new communities harbor abilities or traits that allow them to use resources or tolerate stress in ways that native species cannot. Tradeoffs among species functional traits along the competition–colonization (CC) continuum, where competitive ability is a decreasing function of dispersal capacity, may allow invasive species to establish themselves in new habitats. The California flora offers a well‐characterized model system to examine whether native and exotic species differ in the distribution of functional traits and to examine whether a breakdown of the CC tradeoff is present. We used a random subset of 1000 plants and examined seed traits and life form characteristics along with their seed size and adult height using the Jepson Manual of the plants of California. To test the hypothesis that active dispersal strategies aid in the success of exotic species, we classified species into four seed types according to the presence/absence of mechanisms associated with efficient dispersal. In addition, for each species we compiled data on seed size and adult plant height. We conducted all comparisons between native and exotic species within the four most speciose families to control for potential taxonomic non‐independence. Exotic species had smaller seed size but greater plant height than natives of the same families. On the other hand, exotic species also displayed significantly greater proportions of functional traits that enhanced dispersal ability. Additionally, certain sets of functional traits were significantly associated with exotic species, such as annual life histories with small seeds and high dispersal capacity. In the random subset of the California flora examined, exotics of the most speciose plant families show functional trait combinations that appear to violate the tradeoff structures observed in their California counterparts. Our results suggest that taxonomically controlled comparisons of the CC tradeoff structure between natives and exotic species may shed light of the capacity of those exotic species invasive ability to colonize new habitats.

Climate change and the invasion of California by grasses

AbstractOver the next century, changes in the global climate are expected to have major consequences for plant communities, possibly including the exacerbation of species invasions. We evaluated this possibility in the grass flora of California, which is economically and ecologically important and heavily invaded. We used a novel, trait‐based approach involving two components: identifying differences in trait composition between native and exotic components of the grass flora and evaluating contemporary trait–climate relationships across the state. The combination of trait–climate relationships and trait differences between groups allows us to predict changes in the exotic‐native balance under climate change scenarios. Exotic species are more likely to be annual, taller, with larger leaves, larger seeds, higher specific leaf area, and higher leaf N percentage than native species. Across the state, all these traits are associated with regions with higher temperature. Therefore, we predict that increasing temperatures will favor trait states that tend to be possessed by exotic species, increasing the dominance of exotic species. This prediction is corroborated by the current distribution of exotic species richness relative to native richness in California; warmer areas contain higher proportions of exotic species. This pattern was very well captured by a simple model that predicts invasion severity given only the trait–climate relationship for native species and trait differences between native and exotic species. This study provides some of the first evidence for an important interaction between climate change and species invasions across very broad geographic and taxonomic scales.

HerbariaViz: A web-based client–server interface for mapping and exploring flora observation data

The potential for physical flora collections to support scientific research is being enhanced by rapid development of digital databases that represent characteristics of the physical specimens held in those collections and make this information available remotely. One example is the unified database of California flora observations from the Consortium of California Herbaria that was developed to support the exploration of plant diversity patterns, distribution ranges of species, and vegetation associations for specimens held in physical collections. Many of the records in the herbaria database, and in complementary databases elsewhere, are geo-referenced; but, current web tools for accessing the data do not take advantage of that georeferencing. In this paper, we report on development and implementation of a web-based client–server map interface to facilitate open mapping and exploration of the dataset. Three research objectives were addressed: (1) develop a method for efficient web-map client–server interaction involving large volumes of spatiotemporal point data, (2) develop a symbology and symbol scaling method for representing those spatial–temporal data in the client, and (3) develop an interface for client–server interactions and data exploration. With a focus on cartographically-sound visualization and user-friendly interaction, we introduce HerbariaViz, a web mapping application that provides space–time–species data query responses efficiently. Following a discussion of relevant literature, we present open-source methods for aggregating point data spatially and temporally, outline our approach to sound cartographic representations of those data, and detail the design of a client interface for making requests and mapping responses. A focus group session involving domain experts was performed to provide user evaluation of the application. In our discussion, we present potential avenues of future work, including: facilitating query response comparisons, handling incomplete and inaccurate data, and generalizing the method presented here.

California annual grass invaders: the drivers or passengers of change?

The dominance of invasive species is often assumed to reflect their competitive superiority over displaced native species. However, invasive species may be abundant because of their greater tolerance to anthropogenic impacts accompanying their introduction. Thus, invasive species can either be the drivers or passengers of change.We distinguish between these two possibilities in California grasslands currently dominated by Mediterranean annuals (exotics) and subjected to livestock grazing since European settlement. We focused on native annual grasses and forbs, an understudied species-rich component of the California flora, and Mediterranean annual grasses, currently dominant and among the first non-native plants introduced to the area.We established a field experiment with fenced and unfenced blocks in a cattle pasture. We measured concentrations of limiting resources (nitrogen, phosphorus, light and soil moisture) in monoculture plots as an index of competitive ability (i.e. R*). We then quantified grazing impacts on biomass and seed production in grazed vs. ungrazed monoculture plots. Finally, we measured biomass and seed production of each species competing in mixture plots, in the presence and absence of grazers.We found that native and exotic species did not differ in R* indices of competitive ability, i.e. concentrations of limiting resources in ungrazed native monoculture plots did not differ from concentrations in ungrazed exotic monoculture plots. By contrast, exotic annuals suffered less from grazing than native annuals, perhaps reflecting their longer evolutionary history with cattle grazing. Consistent with these results, native and exotic annuals were equally abundant in ungrazed mixtures, but exotic species overwhelmingly dominated grazed mixtures.Species able to draw down nitrogen and light to lower levels in monocultures (i.e. those with lower R* values) dominated biomass and seeds in mixed plots without grazers. However, R* did not predict the relative abundance of species in grazed plots. Moreover, the relative abundance of species in mixtures did not correlate with grazing impacts on their monocultures, implying that grazing alters inter-specific competitive dynamics.Synthesis. We demonstrate that the displacement of native annuals by Mediterranean annual grasses in California may largely have been driven by cattle grazing.

Range size, taxon age and hotspots of neoendemism in the California flora

AbstractAim Sustaining biological diversity requires the protection of the ecological, evolutionary and landscape‐level processes that generate it. Here, we identify areas of high neoendemism in a global diversity hotspot, the California flora, using range size data and molecular‐based estimates of taxon age.Location California, USA.Methods We compiled distribution and range size data for all plant taxa endemic to California and internal transcribed spacer (ITS)‐based age estimates for 337 putative neoendemics (15% of the endemic flora). This information was combined to identify areas in the state with high proportions of young and restricted‐range taxa. We overlaid the distribution of neoendemic hotspots on maps of currently protected lands and also explored correlations between our diversity measures and climate.Results The central coast of California, the Sierra Nevada and the San Bernardino Range contained endemics with the most restricted distributions on average, while areas in the Desert and Great Basin provinces found within the state were composed of the youngest neoendemics on average. Diversity measures that took age and range size into account shifted the estimate of highest endemic diversity in the state towards the Desert and Great Basin regions relative to simple counts of endemic species richness. Our diversity measures were poorly correlated with climate and topographic heterogeneity.Main conclusions Substantial portions of California with high levels of plant neoendemism fall outside of protected lands, indicating that additional action will be needed to preserve the geographic areas apparently associated with high rates of plant diversification. The neoendemic flora of the deserts appears particularly young in our analyses, which may reflect the relatively recent origin of desert environments within the state.

Fitogeografía de la costa del Pacífico de Norteamérica

This study was designed to explore floristic variation along the Pacific coast from Cook Inlet, Alaska (61o30’N), to the southern tip of Baja California, Mexico, at 23o02’N. Data corresponding to 965 phytosociological releves (including 686 vascular plants) obtained by sampling 279 coastal sites were examined. Using an objective classification system (Average Linkage Clustering) and Sorensen’s index, floristic data acquired in fieldwork were related to the biogeographical regions of the study area. According to the worldwide distribution pattern of genera and species, the registered taxa were grouped into phytogeographical elements. These elements, along with the climatic classification of the sites and comparisons among the main coastal vegetation types, gave rise to a phytogeographical classification of the study area in which four regions (North American Boreal, Rocky Mountain, Californian and Xerophytic-Mexican) and eight floristic provin - ces were distinguished. Each province is characterized by its climate, changes in phytogeographic elements, the presence of endemic genera or species, and by its characteristic vegetation types. Floristic differences among provinces are related to palaeoclimatic and palaeogeographical events. The boreal and temperate provinces show high percentages of broadly distributed elements, whose origins can be found in the Boreotropical or Arctotertiary geoflora that dominated the Northern Hemisphere during the Tertiary. The floristically richest provinces are the three that occupy the Mediterranean zone, since these provinces harbour elements of the Arctotertiary and Madrotertiary geofloras. The flora of tropical Baja California is characterised by a high number of taxa related to Neotropical flora, especially to those showing links with South America.

Notes on California Malvaceae Including Nomenclatural Changes and Additions to the Flora

The writing of revised treatments for selected California Malvaceae for the upcoming second edition of the Jepson Manual and the Flora of North America series (volume 6) has made several nomenclatural changes and explanations necessary. New combinations are made here for taxa in Sidalcea, including Sidalcea asprella subsp. nana, Sidalcea calycosa subsp. rhizomata, Sidalcea celata, and Sidalcea sparsifolia. Several taxa previously included within Sidalcea malviflora have been removed from that species and re-interpreted, resulting in the resurrection and acceptance of the names Sidalcea asprella Greene and Sidalcea elegans Greene. Comments are presented here on the status of Hibiscus lasiocarpos and Lavatera vs. Malva in the California flora. At least one native species has been added to the flora, namely, Iliamna rivularis, though it may no longer occur in the state. Four species of Malvaceae have become naturalized or have been found as waifs in recent years and are added to the flora, namely, Anoda pentaschista, Lagunaria patersonia, Lavatera olbia, and Lavatera trimestris.

Taxonomic Confusion Permits the Unchecked Invasion of Vernal Pools in California by Low Mannagrass (Glyceria declinata)

AbstractChloroplast DNA sequences and recently established morphological characters were used to confirm the widespread invasion of California's vernal pools by European low mannagrass. Morphological similarities between low mannagrass and western mannagrass have led to different taxonomic treatments, depending on the geographical extent of a particular flora. When California's flora was last revised, the two species were combined as western mannagrass, which was then considered to be a native species. Unfortunately, the revised flora was published just as low mannagrass began to rapidly expand its range within the state and, because it was considered to be a native species in the new flora, no actions were initiated to limit the invasion. Our data show that low mannagrass was present at all localities in the Central Valley of California that were investigated, indicating a widespread and undetected invasion. The invasion has led to a degradation of the vernal pool ecosystems, which are the habitat of many federal and state protected endangered and threatened species.

Climate change and the future of California's endemic flora.

The flora of California, a global biodiversity hotspot, includes 2387 endemic plant taxa. With anticipated climate change, we project that up to 66% will experience >80% reductions in range size within a century. These results are comparable with other studies of fewer species or just samples of a region's endemics. Projected reductions depend on the magnitude of future emissions and on the ability of species to disperse from their current locations. California's varied terrain could cause species to move in very different directions, breaking up present-day floras. However, our projections also identify regions where species undergoing severe range reductions may persist. Protecting these potential future refugia and facilitating species dispersal will be essential to maintain biodiversity in the face of climate change.

Palaeoecology of the Miocene El Cien Formation (Mexico) as determined from wood anatomical characters

In order to establish the general environmental conditions under which the plants of the El Cien Formation grew during the Miocene, wood anatomical features from several extant ecological categories (southern California flora) and communities (Brazil, Mexico and Suriname) as well as those of the El Cien paleocommunity were analysed using different statistical approaches. We find a significant correlation between 42 characters of 199 species and 11 climate variables which suggests a close association of wood characters with temperature, whereas characters such as diameter, frequency, and grouping of vessels are more closely related to evaporation. The expression of various wood characters depends on more than one climate variable. There are no doubts regarding the tropical affiliation of the El Cien fossil flora but water availability and seasonality of the system are less clear. Principal component and cluster analyses of two different datasets (423 species, 9 characters and 223 species, 32 characters) suggest that the physiognomy of the fossil assemblage of El Cien was highly efficient in water transport, but also highly vulnerable to embolisms. Characters such as vessel diameter, frequency and grouping suggest proximity to a tropical rain forest, whereas the proportion of ring semi ring porous woods brings the El Cien paleoflora closer to forests with slightly xeromorphic physiognomy, probably a tropical deciduous or semi-deciduous forest. This condition is paralleled with the taxonomic composition of the El Cien fossil plants since their Nearest Living Relatives (NLR) can be referred to both humid or more (seasonally) dry environments. Derived regression analysis models suggest that the paleoflora prospered under conditions with an evaporation regime similar to that of the tropical rain forest.

A NEW SUBSPECIES AND NEW COMBINATION IN FRANGULA PURSHIANA (RHAMNACEAE) FROM THE SIERRA NEVADA, PLUMAS COUNTY, CALIFORNIA

We describe Frangula purshiana (DC.) Cooper subsp. ultramafica J. O. Sawyer & S. W. Edwards, an endemic to the Sierra Nevada in Plumas National Forest, and compare it with other subspecies of F. purshiana. We discuss the use of the generic names Frangula and Rhamnus in the California flora. We also make a new combination Frangula purshiana (DC.) Cooper subsp. annonifolia (Greene) J. O. Sawyer & S. W. Edwards.