Major plant communities of warm North American deserts

Journal of Vegetation Science 6: 79-94, 1995 © IAVS; Opulus Press Uppsala. Printed in Sweden - Major plant communities of some warm North American deserts - 79 Major plant communities of warm North American deserts Peinado, M. 1,2 *, Alcaraz, F.3, Aguirre, J.L.2 & Delgadillo, J.4 1Rancho Santa Ana Botanic Garden, Claremont, CA 91711, USA; 2Present address: Departamento de Biología Vegetal, Universidad de Alcalá de Henares, E-28871 Alcalá de Henares, Spain; 3Departamento de Biología Vegetal, Facultad de Biología, Universidad de Murcia, Spain; 4Facultad de Ciencias, Universidad Autónoma de Baja California, Ensenada, BC, México; *Author for correspondence; Tel. +34 1 8854945; Fax +34 1 8854953 Abstract. A syntaxonomic study of the major plant communities in neotropical North American deserts (Sonoran, Mojave and Baja California Deserts) is presented. The field method of the Braun-Blanquet approach was combined with a numerical syntaxonomical analysis (cluster analysis and principal coordinate ordination). 21 associations are described for the first time: Ambrosio chenopodifoliae-Larreetum tridentatae, Acamptopappo sphaerocephali-Larreetum tridentatae, Hymenocleo monogyrae-Baccharidetum glutinosae, Bergerocacto emoryi-Agavetum shawii, Burseretum hindsianomicrophyllae, Cercidio microphylli-Carnegieetum giganteae, Bursero microphyllae-Cyrtocarpetum edulis, Hymenocleo salsolae-Daleetum spinosae, Echinocereo engelmanniiAgavetum deserti, Euphorbio californicae-Fouquierietum diguetii, Fouquierio splendentis-Larreetum tridentatae, Agavo cerulatae-Idrietum columnaris, Mascagnio macropteraeLysilometum candidae, Maytenetum phyllanthoidis, Opuntio basilaris-Larreetum tridentatae, Prosopidetum torreyanae, Roso minutifoliae-Aesculetum parryi, Opuntio taponaeAgavetum subcerulatae, Tidestromio oblongifoliae-Atriplicetum hymenelytrae, Eurotio lanatae-Larreetum tridentatae and Yucco validae-Fouquierietum diguetii. Some associations include subassociations. Ecological, biogeographical and floristic bioclimatic data are given for each association. Keywords: Arizona Desert; Association; Baja California Desert; Classification; Mojave Desert; Ordination; Phytosociology; Sonoran Desert; Syntaxonomy. Nomenclature: Munz (1973); for Baja California taxa Wiggins (1980); for Agave Gentry (1978). Introduction North American deserts, spread over an area of 1 277 000 km2 in the United States and Mexico, can be climatically divided into two groups: cold deserts and warm deserts (MacMahon 1988). The cold deserts of the central Great Basin, which are Holocene expansions replacing an immense subalpine forest (Wells 1983), are now dominated by Artemisia tridentata and A. arbuscula (sagebrush) or, in drier basins, by Atriplex confertifolia (shadscale). Larrea tridentata (creosote bush) shrubland dominating the warm deserts of North America, also being extensive Holocene expansions, replace Wisconsin pinyon-juniper woodlands (Betancourt et al. 1990). The flora of the warm deserts is derived from subtropical elements and shows affinities with the Neotropics (Daubenmire 1978; Rzedowski 1978; Axelrod 1979; Peinado et al. 1994a). Ecological and botanical studies of the neotropical North American deserts have been the subject of many scientific publications (see Brown et al. 1982) but a floristic-sociological description is not yet available. Since 1988 the authors have applied the Braun-Blanquet method to analyse several western North American biomes. This paper contains descriptions of the main vegetation types (associations) found in warm North American deserts. Study area The study was carried out in desert zones of the United States, mainly Arizona, California, Nevada, New Mexico and Utah, and of Mexico: Baja California Peninsula and northern Sonora (Fig. 1). Despite big differences in geology and topography, the study area is relatively homogeneous regarding geological structure and climate. According to MacMahon (1988) the most obvious feature in the warm North American deserts is that the land surface is dotted with isolated, block-faulted mountains, rising abruptly from debris-filled basins with internal drainages. This feature creates four major geomorphic surfaces: (1) ‘mesas’: isolated flat-topped hills bounded on at least one side by a steep cliff and having an extensive summit area; (2) ‘piedemontes’ or ‘roquedos’: eroded bedrocks at the base of an abrupt hill slope; (3) ‘bajadas’: sheet floods formed by coalesced alluvial fans; and (4) ‘playas’: closed drainage basins in which ephemeral lakes form. Soil particle distribution changes from the top downward to the bottom of the bajadas; coarse materials are found 80 Peinado, M. et al. Fig. 1. Biogeograhy of southwestern North America, modified from Peinado et al. (1994a). Xerofítico-Mexicana (Sonoran) Region: 1. Mojave Province; 2. Colorada Province; 3. Baja Californiana Province; 4. Sanlucana Province; 5. Sinaloo-Sonorense Province; 6. Chihuahuense Province; 7. Californiana Region (7a. Martirense Province); Madrean Region: 8. Sierra Madre Occidental; 9. Sierra Madre Oriental. The surveyed area is included in the provinces 1, 2, 3, 4 and 7a. Top right : Biogeography of Baja California, after Peinado et al. (1994a): I, Californiano-Meridional Province, Diegano Sector. II, Martirense Province: IIa, Juarezense Sector; IIb, Martirense Sector. III, Baja Californiana Province: IIIa, Vizcaíno Sector; IIIb, Angelino-Loretano Sector; IIIc, Magdalenense Sector. IV, Sanlucana Province, Sanlucano Sector. V, Colorada Province, Sanfelipense Sector. at the top and finely divided particles (silt) dominate in the valley of floors and playa beds. The bajadas are the prevailing type, covering 75% of the area (Shreve 1942). Each biogeographical province in the study area is characterized by one or more plant communities inhabiting each of those geomorphic structures. These provinces (Peinado et al. 1994a) are shown in Fig. 1. Climate data on the surveyed area have been summarized by Turner & Brown (1982). All the warm North American deserts are included in zonobiome III (Subtropical desert) of Walter (1985). Two bioclimatic belts (Rivas-Martínez 1993) have been recognized: Mesotropical and Thermotropical. The mesotropical belt spreads over the Colorada (including the Arizona Sector) and Mojave Provinces, penetrating into Baja California up to the northern half of the Vizcaíno Sector (28°) where the thermotropical belt begins. Some mesotropical plant species of the Vizcaíno Sector penetrate into the inframediterranean belt of the neighbouring Martirense Province (Californian Region). This area is a zono-ecotone (Walter 1985) between the subtropical desert and the mediterranean climate zonobiome. Methods The field work was undertaken during seven Spanish-Mexican botanical expeditions to North America between 1989 and 1992. Study sites were selected on the basis of physiognomy, structure and species dominance. Phytosociological relevés were made according to the Braun-Blanquet method (Braun-Blanquet 1979; Westhoff & van der Maarel 1973). Plots were selected in relatively uniform stands and with a size exceeding the minimum area of this type of vegetation (Westhoff & van der Maarel 1973) Relevés were arranged in phytosociological tables (Braun-Blanquet 1979) and associations were detected and characterized. Locations of type relevés are given in the tables (see below). Additional data on 327 unpublished relevés can be obtained from the senior author upon request. For the numerical analysis the cover/abundance values in the scale of Braun-Blanquet were transformed into the 1 - 9 ordinal scale of van der Maarel (1979). Complete linkage clustering was carried out with the programme NCLAS2 (Podani 1988), starting with a matrix that included all 320 vascular taxa recorded in the relevés. With this cluster analysis, results of the preliminary table sorting were improved and some subassociations and floristical variants detected. A synoptic table including 21 associations was elaborated (Table 1). In this table, each taxon is entered with percent constancy values for the various associations it occurs in. Taxa which did not reach a constancy of 33 % in any association were removed. The resultant matrix with 227 taxa was subjected to Principal Coordinate Analysis based on Euclidean Distance (Podani 1988). Each association is defined by a combination of - Major plant communities of some warm North American deserts - 81 Fig. 2. Dendrogram of the Complete Linkage Clustering (Euclidean distance) showing 21 associations and four main vegetation groups. Numerals indicate the number of relevés in each association. Abbreviations of the associations correspond to Table 1. characteristic species including character and differential species. Character species of an association have a distribution which is relatively restricted to that association and are indicative of the association's environment. Differential taxa define associations towards others regardless of their fidelity to the association in question. The concepts of character species and differential species are clear in theory but in practice they can only be significant if the regional floristic-sociological system is well-developed. This is not so in our case and therefore most of our diagnostic taxa are differential, used to distinguish between associations. Character taxa are few and include only some endemics whose distribution is restricted to a specific association. In such a case it is useful to adopt the concept of ‘differentiating floristic combination’ (Beeftink 1965), i.e. a group of taxa differentiating a given association towards all other associations where none of the members of the combination need to be a character taxon. Results and Discussion Of the 21 associations documented in Table 1, 19 can be assigned to one floristic-sociological class which would include all associations of warm deserts. Knapp (1965) presented a syntaxonomical scheme for desert communities, but he did not publish relevés, so detailed comparisons are not possible. Two associations, which are closely related to the Californian Floristic Region (see below), must be excluded from this class, the Roso minutifoliae-Aesculetum parryi and the Hymenocleo monogyrae-Baccharidetum glutinosae. Taking into account the enormous extension of the North American deserts and the absence of phytosociological studies there, further phytosociological analysis in many areas is required before a syntaxonomical outline can be drawn. The floristic groups detected by the agglomerative cluster technique (Fig. 2) and the ordination (Fig. 3), can be grouped into four types, which can be biogeographically, ecologically and climatically characterized. Type I includes relevés from the Pacific side of the Baja California Peninsula between 31° and 28° N, including the northern half of the Vizcaíno Sector and the infra-mediterranean belt of the Martirense province. The associations of this group are characterized by Artemisia californica, Lotus scoparius, Viguiera laciniata, Malosma laurina and Aesculus parryi from northern mediterranean-type ecosystems, which are lacking in the other types. Type I also includes many northwestern Baja Californian endemics or near endemics, such as Bergerocactus emoryi, Agave shawii ssp. shawii, Echinocereus maritimus, Ferocactus fordii, Harfordia macroptera and Cuscuta veatchii. The distribution area of Type I associations has long been considered a transitional zone between mediterranean and desert ecosystems (Shreve 1936; Mooney & Harrison 1972; Peinado et al. 1994a). Even though the true desert vegetation of the Vizcaíno Sector does not pass 30° N, some mesotropical elements, e.g. Ambrosia chenopodifolia, Euphorbia misera, Machaerocereus gummosus, Myrtillocactus cochal, Mammillaria dioica and Simmondsia chinensis reach further north and are important in the infra-mediterranean associations. In Type II we find associations which are mainly dominated by Larrea tridentata (creosote bush) and Ambrosia dumosa, which prevail on the bajadas and well-drained sandy flats of the mesotropical deserts. Because of the combination of high temperature, low precipitation and shallow soils, these associations are typically open and poor in species. The environmental gradient associated with the bajada sequence (Parker 1991) ranges from steep rocky upland sites supporting a diversity of shrubs and cacti - Echinocereo engelmanniiAgavetum deserti - to alluvial flats strongly dominated by one or two species. These alluvial flats are occupied by various Larrea communities. The physiognomy of these communities 82 Peinado, M. et al. Table 1. Floristic composition of the surveyed communities. Scores are I - V constancy-class scale of Braun-Blanquet (1979). Associations No. of relevés Type BE RO ID AC OP UR FO DE AP 9 8 10 12 9 8 9 14 10 I I I II II II II II III Bergerocacto emoryi-Agavetum shawii (BE) Bergerocactus emoryi V Artemisia californica IV Echinocereus maritimus III Dudleya lanceolata III Lotus ♦ scoparius III Roso minutifoliae-Aesculetum parryi (RO) Aesculus parryi . Pityrogramma • viscosa . Agavo cerulatae-Idrietum columnaris (ID) Idria columnaris . Pachycormus • pubescens . Ambrosio chenopodifoliae-Larreetum tridentatae (AC) Ambrosia chenopodifolia V Eriogonum ♦ flavoviride IV Opuntio basilaris-Larreetum tridentatae (OP) Opuntia basilaris . Eurotio lanatae-Larreetum tridentatae (UR) Psilostrophe cooperi . Eurotia lanata . Ferocactus • coloratus . Coldenia • pulchella . Fouquierio splendentis-Larreetum tridentatae (FO) Fouquieria splendens . Echinocereo engelmanii-Agavetum deserti (DE) Agave ♦ deserti . Ferocactus • acanthodes . Acamtopappo sphaerocephali-Larreetum tridentatae (AP) Acamtopappus sphaerocephalus . Tetradymia axillaris . Salazaria mexicana . Ephedra nevadensis . Tidestromio oblongifoliae-Atriplicetum hymenelytrae (TI) Atriplex hymenelytra . Tidestromia oblongifolia . Cercidio microphylli-Carnegieetum giganteae (CA) Carnegiea gigantea . Ambrosia deltoidea . Acacia constricta . Opuntia • thornberi . Opuntia fulgida . Mascagnio macropterae-Lysilometum candidae (LY) Mascagnia macroptera . Lysiloma candida . Ruellia californica . Prosopidetum torreyanae (PR) Prosopis • torreyana . Hymenocleo salsolae-Daleetum spinosae (DA) Dalea spinosa . Hymenoclea salsola . Hymenocleo monogyrae-Baccharidetum glutinosae (BA) Baccharis glutinosa . Hymenoclea monogyra . Tamarix pentandra . Baccharis sarathroides . Nicotiana glauca . Opuntio taponae-Agavetum subcerulatae (TA) Opuntia tapona . Agave ♦ subcerulata . Opuntia invicta . Hibiscus denudatus . Bursero microphyllae-Cyrtocarpetum edulis (CY) Cyrtocarpa edulis . Aeschynomene nivea . Antigonum leptopus . Cnidoscolus angustidens . Bursera cerasifolia . Euphorbio californicae-Fouquierietum diguetii (EU) Prosopis palmeri . Cercidium praecox . Ambrosia bryanthii . Burseretum hindsiano-microphyllae (BU) Bursera hindsiana . Berginia • glandulosa . Yucco validae-Fouquierietum diguetii (YU) Yucca valida . Euphorbia misera V Maytenetum phyllanthoidis (MA) Maytenus phyllanthoides . TI CA LY PR DA BA TA CY EU BU YU MA 8 12 5 10 10 7 7 10 11 7 12 12 III III III III III III IV IV IV IV IV IV III I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I . . . . II . V IV IV V . . . V . II . . . . . . . . . . . . . . . . . . . . . . . . II . . . . . . V . . II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V V IV III . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III IV . III V IV . . III . . . . . . . . . . . . . . . . . . . . . . V V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II . . . . . . . . . . . I IV III IV IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III . . . . . . . . . V IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II . . . . . . . . . . . . . V V III III III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V V V . . . . . . . . . . . . . . . . . . . . II . . . . . . . . . . . . . . . . . V II I . . . . . . . . . . . . . II . . . . . . . III . . . . . II . . V V . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I . . . . . . V V IV. III III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . . . . . . . . V V III III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V IV IV IV III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I . I . IV IV IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III . . . . . V III . . . . . I . I . . . . . . . . . . . . . . . . . . . . . . . . . . III . . . . . V III . . . . . . . . . . . . . . . . . . . . . V - Major plant communities of some warm North American deserts - 83 Table 1. (cont.) Associations No. of relevés Type Thermotropical taxa of Baja Californian communities Opuntia ciribe Jatropha cinerea Fouquieria diguetii Jatropha cuneata Euphorbia • californica Bourreria sonorae Prosopis articulata Ruellia peninsularis Condaliopsis globosa Echinocereus ferreirianus Other taxa Larrea tridentata Opuntia • echinocarpa Lophocereus schottii Simmondsia chinensis Pachycereus pringlei Ambrosia dumosa Krameria • imparata Echinocereus engelmannii Machaerocereus gummosus Pedilanthus macrocarpus Encelia • farinosa Lycium andersonii Lemaireocereus thurberi Cercidium microphyllum Bebbia • juncea Lycium californicum Solanum hindsianum Bursera microphylla Viguiera laciniata Opuntia tesajo Opuntia acanthocarpa Yucca schidigera Ferocactus • gracilis Mammillaria dioica Eriogonum inflatum Opuntia prolifera Agave ♦ cerulata Agave ♦ shawii Rosa minutifolia Myrtillocactus cochal Opuntia bigelovii BE RO ID AC OP UR FO DE AP 9 8 10 12 9 8 9 14 10 I I I II II II II II III TI CA LY PR DA BA TA CY EU BU YU MA 8 12 5 10 10 7 7 10 11 7 12 12 III III III III III III IV IV IV IV IV IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II II . I . . I . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . IV II V IV . . I . . . V V V I III III . IV . . V IV V V V I . III . . III II V V . I I I . II V III V I I . . . . . II III II . II . IV . III . . . . IV I . . . III . . . . . . III I . II . . . . V . V . V IV III . . . . II . . . . . . . . . . . II . . I . . . . . . I . IV V . . IV II IV III IV III . I I I . . . . . I III . III I . . IV III . . IV . . . . V IV III II . III . II . . . . . . . I . . . . . . III . . IV II . . . . V III . . . V I . . . . II . . I . . . . . I II . . IV . . . . . . V II II II . V II . . . . . . . . I . . II III . III . . . . III . . . . V III I II . V I . . . II I . . . . . . . . III I . . . . . . . . . III II . III . V III V . . IV II . I I . . . I I IV II . III I . . . . . III IV I . . . III II I . . . IV . . . . . . . . II III . . III . . . . . . II I . . . . . . . . . . . . I . . . . . . . . . . . . . . . . III II . I . I III II . . II . II V . . . . . . II . . . . . . . . . II . . I . I . . . . . II . I V IV . . . . . . . . . . . . . . . . II . . . . . I . . . . I . . I . . . . . . . . . . . . . . . . II I . . . II . . . . II I . I I . I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II V I . IV . III V V IV IV . II II . I II V . . . . IV . . . . . . III . . . I I IV . . . IV I . . III . . . II V . I . . . . . . . . . . . V III IV . V . . I IV III . . II . . . . IV . II . . . . . . . . . . . III IV III . IV . I I IV II I . III IV I . I V . . . . . I . . . . . . . III . III I III . . I V II . . I . . III II I . II . . II . . . . . . . . . . II II II . . . II III . V . II . . . IV . . . . . . . . . . . . . ♦ = subspecies; • = variety, referring to the following taxa: Agave shawii ssp. goldmaniana; Agave cerulata ssp. nelsonii; Agave deserti ssp. pringlei; Agave cerulata ssp. subcerulata; Atriplex canescens ssp. linearis; Atriplex barclayana ssp. lurida; Bebbia juncea var. atriplicifolia; Berginia virgata var. glandulifera; Cercidium floridum ssp. peninsulare; Coldenia canescens var. pulchella; Croton californicus var. mohavensis; Dalea seemannii ssp. trochilina; Dudleya attenuata ssp. orcuttii; Encelia virginensis ssp. actoni; Encelia californica var. asperifolia; Eriogonum fasciculatum ssp. flavoviride; Eriogonum fasciculatum ssp. polifolium; Ferocactus gracilis var. coloratus; Ferocactus acanthodes var. tortulospinus; Haplopappus venetus ssp. tridentatus; Krameria parvifolia var. glandulosa; Krameria parvifolia var. imparata; Lotus scoparius ssp. brevialatus; Mirabilis bigelovii var. aspera; Opuntia phaeacantha var. discata; Opuntia violacea var. macrocentra; Opuntia echinocarpa var. nuda; Opuntia leptocaulis var. tetracantha; Opuntia acanthocarpa var. thornberi; Pachycormus discolor var. pubescens; Passiflora foetida var. longipedunculata; Pityrogramma triangularis var. viscosa; Prosopis glandulosa var. torreyana; Viguiera deltoidea var. chenopodina; Viguiera deltoidea var. parishii; Viscainoa geniculata var. pinnata. is simple because of the low species diversity and the wide spacing of the shrubs. Although the creosote-bush vegetation appears as monotonously uniform throughout its area, there are significant regional differences in its floristic composition, most of them related to biogeographical variation, that allow several associations to be distinguished. Type III is fairly heterogeneous; both multivariate methods place together many associations which, for different reasons, have a low floristic similarity. The Acamptopappo sphaerocephali-Larreetum tridentatae association corresponds to a widespread plant community in the Mojave Desert; since the Mojave Desert scrub biome is intermediate between the Great Basin desert scrub and the Sonoran desert scrub (Thorne 1986), the Mojavan association contains several taxa (Table 14) that are lacking in other desert associations. The Cercidio microphylli-Carnegieetum giganteae is the dominant association of the Arizona Sector (Colorada Province), which is moister than other desert sectors (Turner & Brown 1982). The vegetation has the appearance of a shrubland or low woodland of leguminous trees and giant cacti. Many of these tree species are confined to runnels and washes in more arid provinces, e.g. Cercidium microphyllum, C. floridum, Olneya tesota, Prosopis ssp. and Acacia spp. As a result, the Cercidio microphylli-Carnegieetum giganteae is united with associations restricted to moist places. The Tidestromio oblongifoliae-Atriplicetum hymenelytrae is floristically the poorest association; it grows in the most arid zones of the North American deserts. Type IV includes six associations based on a very homogeneous group of taxa, i.e. thermotropical taxa as listed in Table 1. All these associations occur in the thermotropical belt of Baja California. 84 Peinado, M. et al. Fig. 3. Principal coordinate analysis showing the position of the associations in the ordination plane of axes 1 and 2. Association abbreviations as in Table 1. Description of associations Bergerocacto emoryi-Agavetum shawii ass. nova; nomenclatural type: Table 2, rel. 2 The association is dominated by succulents such as Agave shawii ssp. shawii, Bergerocactus emoryi, Mammillaria dioica, Opuntia prolifera, O. littoralis, Myrtillocactus cochal and Machaerocereus gummosus, as well as low-growing, shallow-rooted, often aromatic, droughtdeciduous shrubs such as Artemisia californica, Eriogonum fasciculatum ssp. flavoviride and Lotus scoparius ssp. scoparius. It corresponds to the ‘coastal succulent scrub’ (Axelrod 1978; Westman 1983). The subassociation idrietosum columnaris (subass. nova; nomenclatural type: Table 2, rel. 10) forms a transition to the Agavo cerulatae-Idrietum columnaris; it corresponds to the ‘maguey-boojum series’ of Turner & Brown (1982). The association is found in the mesotropical belt of the Vizcaíno Sector and in the infra-mediterranean belt of the Martirense Province as far north as 31° N at Punta Colonet. Roso minutifoliae-Aesculetum parryi ass. nova; nomenclatural type: Table 3, rel. 8 This association is characterized by the floristic combination of deciduous low trees (Aesculus parryi) and shrubs (Rosa minutifolia), together with succulents such as Bergerocactus emoryi and Agave shawii ssp. shawii. This is an infra-mediterranean chaparral association of the Martirense Province. Its main distribution area is the zone between Cabo Colonet and El Rosario, Baja Cali- fornia. It is also found in the mesotropical desert areas of the Vizcaíno Sector as a permanent community in shady or moist microhabitats. The northern part of the Vizcaíno Desert is considered a chaparral-desert ecotone with several chaparral species penetrating into the desert in habitats with relatively moist soils (Shreve 1936; Turner & Brown 1982). The Roso minutifoliae-Aesculetum parryi and the Bergerocacto emoryi-Agavetum shawii associations occur in the infra-mediterranean-mesotropical ecotone forming a topographic mosaic in which the former association occupies relatively wet, shady places, while the latter association regularly inhabits the driest sites, such as sunny hillsides, steep southern slopes covered with thin soil, rocky areas or exposed sea bluffs. The variant of Frankenia palmeri (rel. 3) on alkaline soils, is a transition to the halophilous Atriplici julaceaeFrankenietum palmeri (Peinado et al. 1994b). Ambrosio chenopodifoliae-Larreetum tridentatae ass. nova; nomenclatural type: Table 4, rel. 4 Like other communities growing on lower bajadas, the Ambrosio chenopodifoliae-Larreetum tridentatae is a floristically poor association, especially when compared with the bordering piedmont association Agavo cerulatae-Idrietum columnaris. Larrea tridentata and Ambrosia chenopodifolia are the dominant species and some Baja California endemics, notably Opuntia prolifera, Agave cerulata ssp. cerulata and Ferocactus gracilis var. gracilis, are good differential species against other, ecologically similar, associations. - Major plant communities of some warm North American deserts - 85 Table 2. Bergerocacto emoryi-Agavetum shawii ass. nova. Type relevés: association, rel. 2: Fish Camp, Punta Colonet, May 13, 1992; subassociation idrietosum columnaris, rel. 10: Valle de los Cirios, between El Rosario de Abajo and Mesa la Pitahaya, May 10, 1992; both in Baja California. ♦ subspecies; • variety; * Baja California endemic. Table 3. Roso minutifoliae-Aesculetum parryi ass. nova. Type relevé: 8, Punta Baja, El Rosario, Baja California, May 20, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa Roso minutifoliae-Aesculetum parryi: Differentiating floristic combination Aesculus parryi * 3 2 3 2 3 3 2 2 Rosa minutifolia 2 4 + + 2 3 + 2 Pityrogramma • viscosa . . . 1 1 . 1 1 1 2 3 4 5 6 7 8 9 120 90 30 120 110 60 110 - 110 100 100 100 100 100 100 100 200 100 21 17 22 24 17 19 20 18 20 10 120 100 20 Bergerocacto emoryi-Agavetum shawii: Differentiating floristic combination Agave ♦ shawii * 3 2 2 2 2 3 2 2 1 Bergerocactus emoryi * 1 2 1 2 2 1 2 + 2 Euphorbia misera 2 2 2 2 . 1 2 1 . Echinocereus maritimus * 1 1 1 1 1 1 . + 1 Rosa minutifolia 3 + 3 3 4 3 3 . . Artemisia californica 1 2 + 1 + 2 1 . . Lotus ♦ scoparius 1 . 1 + + . 1 . . Rhus integrifolia . . + + . . 1 + . Opuntia littoralis 2 + + . . . . . 1 Stipa lepida 1 . 1 1 1 . . . . Ferocactus ♦ fordii * + 1 1 . . + . . . 3 + 2 . . . . . . . . Bergerocacto emoryi-Agavetum shawii idrietosum columnaris Idria columnaris * . . . . . . . Pachycereus pringlei . . . . . . . . . 3 1 3 2 Baja California endemics Myrtillocactus cochal * Harfordia macroptera * Aesculus parryi * Cneoridium dumosum * Dudleya ♦ orcuttii * Opuntia rosarica * Atriplex julacea * Eriogonum fastigiatum * Mammillaria brandegeei * Cuscuta veatchii * Haplopappus rosaricus * . . . . . . . 2 . 1 . . . r . . . 2 . . . . 1 1 . . . . . . . . . 2 1 . + . . . . . . . + . . . . . . . 1 . . . 1 . . . + . . . . . 1 . . . . . . . . . . . . r . . + . . . . 1 . . r 1 + . . . . . . . . . 1 1 . . . . . . Other taxa Mammillaria dioica Opuntia prolifera Ambrosia chenopodifolia Eriogonum ♦ flavoviride Simmondsia chinensis Dudleya lanceolata Lycium californicum Ephedra californica Malvastrum coromandalianum Machaerocereus gummosus Encelia californica Mirabilis • laevis Viguiera laciniata Peucephyllum schottii Solanum hindsianum Trixis californica Opuntia • acanthocarpa Ferocactus • acanthodes Lycium andersonii Stipa diegoensis 1 + . 2 2 2 . . 1 . . 1 . 1 . . . . . 1 1 2 3 1 . 1 1 . + . . . . . . . . . . . 1 + 3 2 1 1 . + . 2 . . + . . . . . . . 1 1 2 + 2 1 1 . + . 2 1 . 1 . . . . + . 1 + + 2 2 1 . . . . . . . 1 . . . . . . 1 1 2 1 . . 1 . + 2 + 1 . . . . . . 1 . 1 + + 1 2 . + + . . . . 1 . . + . . . 1 1 1 1 . 1 1 + + . 1 . . . . + . . + . . 1 2 3 1 2 . + + . . 2 . . . 2 1 1 . . . 1 2 2 1 2 . . + 1 2 2 . 2 . 2 . 1 2 . . Additional taxa: Selaginella lepidophylla (rel.7: 1), Selaginella cinerascens (5: 1), Dudleya pulverulenta (7: +). This creosote-bush association occurs on welldrained sandy flats, bajadas and upland slopes in the warm deserts. It is the typical creosote-bush association in the mesotropical zones of the Vizcaíno Sector. In some localities of northern Vizcaíno (San Agustín area), where deep-buried calcareous layers occur, we find a floristical variant with an undescribed taxon of the genus Yucca, i.e. Yucca schidigera sensu Wiggins (1980). This variant (Table 4, rels. 6 - 9) substitutes the Eurotio lanatae-Larreetum tridentatae in places where calcareous layers reach the surface. Relevé no. Altitude (m) Area (m2) No. of taxa 1 2 3 4 120 170 30 270 50 50 50 100 6 13 9 4 5 6 7 200 200 530 100 100 100 7 6 4 8 60 50 12 Roso minutifoliae-Aesculetum parryi variant of Frankenia palmeri Atriplex julacea * . . 2 . . . . Frankenia palmeri . . 2 . . . . Lycium californicum . . 4 . . . . . . . Baja California endemics Agave ♦ shawii * Bergerocactus emoryi * Opuntia littoralis * Cuscuta veatchii * Ferocactus • fordii * 3 2 1 . . 1 1 . . . . + . . + . . . . . + 1 . . . + . + . . . . . . . 2 . . 1 . Other taxa Ambrosia chenopodifolia Malosma laurina Ribes tortuosum Simmondsia chinensis Stipa lepida 2 . . . . . . . 2 1 . . . . . . . 1 . . 2 . 1 . . + + . . . . 3 . . . . 2 . 2 . Additional taxa: Allium haematochiton (rel. 1: 2), Artemisia californica (2: 2), Dichelostemma pulchellum (3: 1), Dudleya cultrata (3: 2), Encelia californica (8: 2), Eriogonum ♦ fasciculatum (2: 8), Euphorbia misera (2: 2), Grossularia speciosa (8: 1), Haplopappus ♦ tridentatus (2: 1), Isomeris arborea (8: 1), Malacothamnus fasciculatus (8: 1), Opuntia prolifera (2: +), Rhus integrifolia (8: 4), Viguiera laciniata (2: 1). Table 4. Ambrosio chenopodifoliae-Larreetum tridentatae ass. nova. Type relevé: 4, between Punta Prieta and Chapala, Baja California, May 5, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 2 3 4 5 6 7 8 9 10 650 740 500 500 550 500 500 500 500 590 100 100 100 100 100 100 100 100 100 100 10 6 10 13 14 11 11 12 11 6 Ambrosio chenopodifoliae-Larreetum tridentatae: Differentiating floristic combination Ambrosia chenopodifolia 2 1 + 1 1 Larrea tridentata 2 2 1 2 2 Eriogonum ♦ flavoviride 1 . 1 2 1 1 2 + 1 2 1 + 2 + 1 2 + 2 2 1 Other taxa Fouquieria splendens Opuntia prolifera * Opuntia • echinocarpa Ambrosia dumosa Ferocactus • gracilis * Lophocereus schottii Yucca schidigera Agave ♦ cerulata * Asclepias subulata Simmondsia chinensis Echinocereus engelmannii Opuntia cholla Beloperone californica Viguiera • chenopodina * + 1 1 2 + . 2 . 1 . + . . . 1 1 1 2 + . 2 . 1 . + . . . 1 1 1 2 . . 2 1 + . + . . . 1 1 1 2 + . 2 . 1 . + . . . . + . . + + . . . . . . . . . . . 2 . 1 . . . 1 . . . . . . 1 . . 1 . . . . . . . . 2 . . 2 . + . 2 . + . . . . 1 + 1 . + + . 1 . + . 1 + 1 2 + 1 . + + 2 1 . + . 1 + + Additional taxa: Ambrosia camphorata (rel. 1: 1), Atriplex polycarpa (1: 1), Dalea spinosa, (3: 1), Encelia farinosa (3: 1), Ferocactus • tortulospinus (1: +), Idria columnaris * (8: 1), Lycium andersonii (1: 1), Lycium californicum (1: 1), Proboscidea althaefolia (2: +). Eurotio lanatae-Larreetum tridentatae ass. nova; nomenclatural type: Table 5, rel. 1 This is another creosote bush association occurring in mesotropical areas of the Vizcaíno Sector with the differential species Eurotia lanata closely restricted to 86 Peinado, M. et al. Table 5. Eurotio lanatae-Larreetum tridentatae ass. nova. Type relevé: 1, Rancho Sonora, San Agustín area, N Vizcaíno, Baja California, May 6, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 590 50 14 2 550 50 14 3 540 100 18 4 500 100 10 5 470 50 10 6 510 50 11 7 8 650 550 50 50 13 15 Eurotio lanatae-Larreetum tridentatae: differentiating floristic combination Eurotia lanata 1 1 1 1 1 1 2 Larrea tridentata 1 1 2 1 1 2 2 Psilostrophe cooperi + + 1 1 1 2 1 Coldenia • pulchella 1 1 1 . . . . 2 1 + 1 Baja Californian endemics Ferocactus • coloratus Opuntia tesajo Agave ♦ cerulata Agave ♦ goldmaniana Yucca valida Haplopappus odontolepis Opuntia molesta Dalea megalostachya Krameria • parvifolia Mirabilis cedrodensis Viguiera purissimae 1 + 1 . . . + . . . . + 1 1 1 . . . . . . . + . + + . . . . . . . + + . . . . . . . . . + + . . . + + . . . . . 1 . . . . . 1 1 . . + . . . 1 1 . . . 1 . . . 1 . + . . . . . + Other taxa Ambrosia dumosa Eriogonum ♦ flavoviride Fouquieria splendens Yucca schidigera Polygala desertorum Krameria • imparata Viguiera laciniata Ephedra californica Eriogonum trichopes Lophocereus schottii Lycium megacarpum Opuntia • echinocarpa Porophyllum gracile Simmondsia chinensis 1 + 1 1 . . . . . . + . + . 2 1 1 . . + 1 . . . . . . 1 2 1 2 + 2 + + + . + + . . 1 1 1 . + . . . . . . . . . . 2 1 . 1 . . . . . . . . . . 2 1 . . 2 . . 1 1 . . . . . 2 1 . . . . . . 1 + . 1 . . 2 1 2 . 1 1 + . . . . + 1 . Additional taxa: Atriplex polycarpa (rel. 4: 1), Lycium californicum (4: 1), Sphaeralcea ambigua (7: 1). layers commonly called ‘caliche’, a kind of soil-holding accumulated calcium carbonate. The association is floristically poor because caliche retards the penetration of water and interferes with the development of the root system, making the habitat arid (Breazeale & Smith 1930; Shreve & Mallery 1933). Although this association is most typical for the Vizcaíno Sector, the differential species for that Sector, Psilostrophe cooperi and Eurotia lanata, also occur in other Mojave communities, where they always indicate buried layers of caliche (Table 14, rels. 4 - 6 and 10). Agavo cerulatae-Idrietum columnaris ass. nova; nomenclatural type: Table 6, rel. 5 This species-rich community is dominated by Idria columnaris, the succulent, up to 20 m tall, boojum tree, together with 4 - 5 m tall plants of various growth forms - Pachycormus discolor var. pubescens, Pachycereus pringlei and Lophocereus schottii - giving it the appearance of an open succulent woodland. In between these dominants, succulents and shrubs occur such as Agave cerulata ssp. cerulata, Larrea tridentata, Opuntia cholla, Opuntia molesta and Harfordia macroptera. Pachycereus pringlei, a giant columnar cactus, is vicariant to Table 6. Agavo cerulatae-Idrietum columnaris ass. nova. Type relevés: association: rel. 5, 20 km N of Cataviña, May 6, 1991; subassociation yuccetosum validae, rel. 8, Km 278, Transpeninsular road, on sandy soil, July 2, 1992. Both in Baja California. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 2 3 4 5 6 7 8 9 10 80 570 600 640 630 540 120 400 260 140 100 100 200 100 100 100 100 100 150 100 10 18 18 15 19 17 20 19 17 15 Agavo cerulatae-Idrietum columnaris: Differentiating floristic combination Idria columnaris * 1 2 1 3 2 2 3 1 1 Pachycormus• pubescens * 2 3 3 . 2 . 3 1 1 Agave ♦ cerulata * 1 2 . 2 1 1 . 2 . 1 + . Agavo cerulatae-Idrietum columnaris yuccetosum validae Opuntia ciribe * . . . . . . Yucca valida * . . . . . . Fouquieria diguetii . . . . . . Jatropha cinerea . . . . . . Jatropha cuneata . . . . . . 2 2 1 . . 1 2 + . 1 2 + 2 2 . 2 2 . . . Baja California endemics Ferocactus • gracilis Agave ♦ goldmaniana Viscainoa • geniculata Opuntia molesta Ferocactus • coloratus Harfordia macroptera Opuntia tesajo Krameria • parvifolia Agave ♦ nelsonii Cuscuta veatchii Viguiera • chenopodina Encelia • asperifolia Ferocactus • tortulospinus Mammillaria blossfediana Opuntia invicta Viguiera purissimae . 2 . . 1 . . . . . . . . . . . 1 1 . . . 1 . . . . . . . . . . 1 . . . . . 1 . 2 . . . . . . . 1 . . . . . . 2 . . . . . . . 2 1 . 1 + . . . . . 1 2 . + . . . 1 . . 1 . 1 + . . . . . . . . . . 1 . . 1 . . . . . . . . . . . . 2 2 . . . . . . . . 1 . . . . . . 2 1 . . . . . . . . . . . . . . 2 . . . . . . . . . . 1 + . Other taxa Larrea tridentata Ambrosia chenopodifolia Mammillaria dioica Pachycereus pringlei Lophocereus schottii Eriogonum ♦ flavoviride Fouquieria splendens Ambrosia dumosa Simmondsia chinensis Machaerocereus gummosus Ambrosia camphorata Pedilanthus macrocarpus Viguiera laciniata Encelia farinosa Opuntia cholla Opuntia• echinocarpa Lycium californicum Euphorbia misera Solanum hindsianum Condalia globosa Acalipha californica . 1 + . . . . . . 1 . . . . . . 1 1 . . . + 1 1 1 . 1 . . 1 . 1 + . + . 1 + . . + . 1 + 1 . + + + 1 + . + . + 1 . . . . 1 + . + 2 + 1 1 1 3 2 . . . . 1 . + . . . . . . 1 2 . 2 1 2 1 + 1 . . . . . . . . . + . 1 1 2 + + 1 2 + . 1 . 2 . 1 . 1 . . . . . . 1 + 1 1 1 1 . . + 2 . 1 + . 2 . 1 + . . . 1 1 + 2 + . . . . 2 . 1 . . . + . 1 . . . 1 . + 1 + . 1 1 . . + . . + . . . . . . 1 1 . . 1 + . 1 2 . 2 . 1 . . . + . . . . . Carnegiea gigantea, the character-species of the Arizonian Cercidio microphylli-Carnegieetum giganteae. The association flourishes on granitic and basaltic soils in mesotropical northern and central Vizcaíno. It corresponds to the ‘agave-boojum series’ (Turner & Brown 1982), The yuccetosum validae subassociation (subass. nova; nomenclatural type: Table 6, rel. 8) occurs in transitional areas between the typical subassociation and the thermotropical Yucco validae-Fouquierietum diguetii association. It is found on sandy soils at the southern border of the mesotropical part of the Vizcaíno Sector, and the differential species are thermotropical taxa such as Yucca valida, Opuntia ciribe and Fouquieria diguetii. - Major plant communities of some warm North American deserts Table 7. Yucco validae-Fouquierietum diguetii ass. nova. Type relevés: association, rel. 3: Between Ejido Mújica and Ejido Vizcaíno, Baja California Sur, July 3, 1992; subassociation agavetosum goldmanianae, rel. 9: Track to Santa Rosalillita, Baja California, July 2, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 2 3 4 5 6 7 8 9 10 100 140 80 70 170 100 80 60 70 90 150 150 150 150 150 100 150 150 150 150 12 18 13 17 13 11 13 11 17 14 Yucco validae-Fouquierietum diguetii: Differentiating floristic combination Fouquieria diguetii 2 2 2 1 1 2 2 . 1 Yucca valida * 1 1 1 1 2 2 + 1 1 Machaerocereus gummosus 2 2 1 1 1 2 2 1 1 1 1 + Yucco validae-Fouquierietum diguetii agavetosum goldmanianae Agave ♦ goldmaniana * . . . . . . 2 Echinocereus maritimus * . . . . . . 1 Ambrosia chenopodifolia . . . . . . 2 Pachycormus • discolor * . . . . . . . 1 1 1 + 1 1 2 2 1 + . . Thermotropical taxa Opuntia ciribe * Jatropha cinerea Opuntia invicta * Ambrosia magdalenae * Encelia halimifolia Mammillaria hutchinsoniana * Tillandsia recurvata Atamisquea emarginata Krameria • parvifolia * Pithecellobium mexicanum 2 2 + . . + . + . . 1 1 1 1 . + 1 . . . 1 + 1 . 1 + + . . . 1 1 + + 1 . . . . . . 2 . . . . . . 1 + 2 2 . . 1 . . . . . + . . . . . . . . . . . . . . . . . . . 1 + . 1 . . . . . . + . . 1 . . . . . . Other taxa Lycium californicum Pedilanthus macrocarpus Pachycereus pringlei Euphorbia misera Larrea tridentata Lophocereus schottii Ferocactus • gracilis * Viguiera • parishii Frankenia palmeri Echinocereus engelmannii Encelia palmeri * Ferocactus • coloratus * Opuntia tesajo * Solanum hindsianum Cercidium microphyllum Lemaireocereus thurberi Atriplex julacea * Abronia maritima Gasoul crystallinum Atriplex ♦ lurida * 1 . 1 . 1 1 . . . . . . . . . . . . . . 1 1 1 . . + + 1 . . + . . . . . 1 . . 1 2 . 1 . + + . . . . . . . . . . . . . . . + 1 . + . 1 . . + . . . + + + . . . . . 1 1 . 1 . . . . + 1 . . . + + . . . . 2 . . 2 . 1 . . . . . . . . . . . 1 1 . 2 . . 1 . . . . + . . 1 . . . . . + 1 . . . . 1 . . . 2 . . . + . . . . 1 . . 1 . + . + 1 . 1 . 1 . . . + + . . . . . . . . . 1 . . 1 1 1 . . . + . . . 1 . . . 87 Table 8. Opuntio taponae-Agavetum subcerulatae ass. nova. Type relevé: 4, track from Transpeninsular road to San Francisco de la Sierra Km 17, Baja California Sur, July 3, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 160 100 19 2 250 100 16 3 760 100 21 4 540 100 20 5 1040 100 21 6 140 100 22 7 170 100 13 Opuntio-Agavetum subcerulatae: Differentiating floristic combination Agave ♦ subcerulata * 1 2 2 2 2 1 Opuntia tapona * + + + 2 + 1 2 1 Thermotropical taxa Bursera microphylla Fouquieria diguetii Opuntia ciribe * Jatropha cuneata Bursera hindsiana Opuntia invicta * Euphorbia magdalenae * Jatropha cinerea Phitecellobium mexicanum Mammillaria hutchinsoniana * Jacquemontia abutiloides Alvordia glomerata * Mammillaria capensis * 2 1 1 . 1 + . + . 1 1 . . 2 2 1 + . . 1 . . . . . . 1 1 + + + . 1 . 1 . . . . 2 2 + + + 1 . . . . . . . + 1 . 1 . . . . + . . 2 . 1 1 2 . + 2 . 1 . . . . 1 2 . . + . . . . . + . . . Other taxa Machaerocereus gummosus Echinocereus engelmanii Opuntia • echinocarpa Ferocactus • gracilis * Pachycereus pringlei Encelia farinosa Pedilanthus macrocarpus Hibiscus denudatus Krameria • imparata Myrtillocactus cochal * Ambrosia camphorata Viguiera • deltoidea * Ferocactus rectispinus * Atriplex ♦ barclayana Larrea tridentata Lemaireocereus thurberi Solanum hindsianum Viguiera purissimae * Cercidium microphyllum 2 1 + . 1 + + 1 . . . . . . . . . . . 2 . + + 1 2 . + . + . . . . . + + . . 1 1 1 1 + . . . + + 2 2 + . . . . . + 2 1 + 1 1 1 1 + . . 2 . . . + 1 . 2 . . 2 + + . 1 1 . + + . 1 + . . . . . . 2 + 1 . 2 1 1 . . . . . . 1 1 . 1 1 + + 1 . + . . + + + . . . . + . . . . . Additional taxa: Calliandria californica (rel. 5: 1), Croton californicum (6: +), Croton magdalenae * (5: 1), Dalea ♦ seemannii (8: 1), Encelia palmeri * (1: +), Ficus palmeri * (5: +), Idria columnaris * (5: 1), Justicia hians * (5: 1), Lophocereus schotii (3: +), Trixis angustifolia * (6: 1), Viscainoa • geniculata * (1: +). Additional taxa: Dudleya gatesii * (rel. 8: 1), Krameria • imparata (4: 1). Yucco validae-Fouquierietum diguetii ass. nova; nomenclatural type: Table 7, rel. 3 The vegetation is rather uniform with 2 - 4 m tall Yucca valida (datilillo) and Fouquieria diguetii (ocotillo). The big cacti Machaerocereus gummosus, Lemaireocereus thurberi and Lophocereus schottii are conspicuous members of this association which occurs on the thermotropical coastal sandy plains of the Vizcaíno Sector. This coastal area is often foggy, and the epiphyte Tillandsia recurvata and several lichens hang densely from the dominants or even cover the soil surface. On extensive coastal flats with alkaline soils within the area of this association, the halophytic Atriplici julaceae-Frankenietum palmeri Peinado et al. 1994 occurs; transitions between both Vizcaíno associations (Table 7, rels. 2 and 10) have been labelled as ‘frankeniadatilillo-ocotillo series’ (Turner & Brown 1982). The subassociation agavetosum goldmanianae (subass. nova; nomenclatural type: Table 7, rel. 9) is found on granitic and volcanic soils in the northernmost coastal areas. It is differentiated by mesotropical taxa such as Ambrosia chenopodifolia and further by Agave shawii ssp. goldmaniana. Opuntio taponae-Agavetum subcerulatae; nomenclatural type: Table 8, rel. 4 This association is characterized by some thermotropical Vizcaíno endemics, notably Agave cerulata ssp. subcerulata, Opuntia tapona and O. invicta. It occurs on volcanic outcrops which are found inland in the wide sandy plain dominated by the Yucco-Fouquierietum. The association can be considered a vicariant of the coastal subassociation Yucco validae-Fouquierietum diguetii agavetosum goldmanianae. It is distributed in the southern half of the Vizcaíno Desert (28 - 26° N). 88 Peinado, M. et al. Table 9. Burseretum hindsiano-microphyllae ass. nova. Type relevé: 4, Santispac, near Bahía Concepción, Baja California Sur, July 4, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 2 3 4 5 6 7 8 9 10 90 60 70 60 30 220 50 10 320 60 150 150 150 150 150 150 150 150 150 150 13 12 19 11 15 16 18 14 14 11 Burseretum hindsiano-microphyllae: Differentiating floristic combination Bursera microphylla 1 1 1 1 2 1 2 1 2 Bursera hindsiana 1 1 1 1 1 1 2 2 + Fouquieria diguetii 2 1 1 1 1 1 1 1 2 1 1 1 Thermotropical taxa Jatropha cuneata 1 Opuntia ciribe * . Jatropha cinerea . Berginia • glandulifera * + Atamisquea marginata . Ruellia californica . Jacquemontia abutiloides . Caesalpinia pannosa * . Condalia brandegeei * . Aeschynomene nivea * . Castela peninsularis * . Cochemia poselgeri * . Cyrtocarpa edulis * . Echinocereus brandegeei * . Pachycereus pecten-aboriginum. Ruellia peninsularis . 1 . . . . . . . . . . . . . . . 1 2 + + + + + . 1 . . . . . . . 1 2 . . . . . . . . . . . . . . 1 . . + . 2 . 2 . . . . . . . . 1 . . 1 . 1 + . . . . . . . . . 1 1 . . 1 . . . . + + + + + + 1 2 . 2 . . . . . . . . . . . . . 1 2 2 . + . . . . . . . . . . . 1 2 1 . . . . . . . . . . . . . Other taxa Cercidium microphyllum Pachycereus pringlei Machaerocereus gummosus Larrea tridentata Opuntia • echinocarpa Lemaireocereus thurberi Lophocereus schottii Dalea ♦ seemannii Cordia parvifolia Pedilanthus macrocarpus Bebbia • juncea Prosopis articulata Fagonia barclayana Fagonia laevis + 1 1 1 + 1 1 . . . . . . 1 1 . 1 + . . . . + + . . . + 1 1 1 1 . 1 . 1 . . . . . . 1 + . . . + . 2 1 . 1 . 1 . 1 + . . + 1 + . . . . . 2 . . . 2 . + + . . . 1 . 1 . . 2 + . . + . . 1 . . 1 2 . . . . 2 1 1 + + . + 1 . . . . 1 1 1 1 . . . 1 . . . . . . + 1 + 1 1 . + . . . . . . . Additional taxa: Bourreria sonorae (rel. 6: 1), Cissus trifoliata (6: r), Echinocereus engelmannii (1: r), Encelia • farinosa (5: 1), Hyptis • emoryi (8: 1), Janusia californica (6: 1), Mammillaria dioica (3: +), Pachycormus • pubescens * (8: 1), Prosopis • torreyana (1: r), Solanum hindsianum (3: +), Viscainoa • geniculata * (8: 1). Burseretum hindsiano-microphyllae ass. nova; nomenclatural type: Table 9, rel. 4 This thermotropical association is dominated by 3 - 4 m-high small trees, called torchwoods: Bursera hindsiana and B. microphylla, by large shrubs: Fouquieria diguetii, Jatropha cinerea and J. cuneata, and by the columnar ‘cardón’ Pachycereus pringlei. It corresponds to the sarcocaulescent desert (Wiggins 1980) and the ‘torchwood-cardón series’ (Turner & Brown 1982). It occurs on deep soils of granitic or volcanic origin in the Angelino-Loretano Sector. Cercidium microphyllum can be co-dominant on deep granitic soils, but is absent on the volcanic or eroded hill slopes. A floristical variant with Cyrtocarpa edulis (rel. 7) corresponds to the southern disjunction of this association near Bahía de la Paz. Euphorbio californicae-Fouquierietum diguetii ass. nova; nomenclatural type: Table 10, rel. 7 This desert scrub association has few species in the differentiating combination. The absence of Bursera hindsiana is a differential feature toward the Burseretum Table 10. Euphorbio californicae-Fouquierietum diguetii ass. nova. Type relevés: association, rel. 7: near Estación microondas El Rifle, July 5, 1992; subassociation cercidietosum praecocis, rel. 5: El Coyote, July 5, 1992. Both in Baja California Sur. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 2 3 4 5 6 7 8 9 10 240 110 40 30 30 30 110 80 90 20 100 100 100 100 100 100 100 100 100 100 14 23 18 11 19 17 14 9 16 12 Euphorbio californicae-Fouquierietum diguetii: Differentiating floristic combination Euphorbia • californica 1 1 1 1 1 1 1 1 1 1 Fouquieria diguetii 2 1 1 1 1 1 2 1 1 1 Ambrosia bryantii * . + 2 1 1 . 1 . 2 + Euphorbio californicae-Fouquierietum diguetii cercidietosum praecocis Prosopis palmeri * 2 2 2 1 2 . . . Cercidium praecox 2 1 + 1 2 . . . Ruellia peninsularis 2 1 1 . 1 . . . Thermotropical taxa Opuntia ciribe * 2 2 1 2 2 1 1 + Jatropha cinerea . + 1 . 2 1 1 . Jatropha cuneata 2 1 1 . 1 1 1 1 Bursera microphylla 1 1 . . . + 1 1 Tillandsia recurvata . 1 + . . + . . Ferocactus • townsendianus * . . . . . . + . Mammillaria capensis * . + + + . . . + Atamisquea marginata . 1 . . 1 . . . Acacia brandegeana * . . . . . 1 . . Berginia • glandulifera * . . . . 1 1 . . . . . . . . 1 1 1 1 . + . . 1 . 1 1 . + . . . + . . Other taxa Larrea tridentata Pachycereus pringlei Machaerocereus gummosus Lophocereus schottii Pedilanthus macrocarpus Lemaireocereus thurberi Opuntia • echinocarpa Encelia palmeri * Ambrosia camphorata Euphorbia tomentulosa Lycium megacarpum Eriogonum repens * Janusia californica Krameria • glandulosa Opuntia tesajo * 1 1 . + . 1 + . . . + . . . + 1 1 1 . 1 + . . . . . . . . . . 1 1 . . 1 1 . . 1 . . 1 . . 1 1 1 1 1 1 . . + 1 . . . . + 1 1 2 1 1 . . . . . + . . . . 1 + 1 1 . . . . . . . . . . . 2 . 1 1 1 . + 1 1 . . . . . . 2 + + + . . + 1 . . . 1 . + . 1 1 1 1 1 . . . . . . . + . . 1 . . . . . . . . . . + . 1 . Additional taxa: Bourreria sonorae (rel. 3: r), Cissus trifoliata (5: r), Echinocereus engelmannii (2: r). hindsiano-microphyllae; the lack of Yucca valida and the frequency of Euphorbia californica are differential characters toward the Yucco validae-Fouquierietum diguetii. It occurs in the Magdalenense Sector, in a plain with rainfall generally less than 200 mm/yr. Besides the typical subassociation, a cercidietosum praecocis subassociation (subass. nova; nomenclatural type: Table 10, rel. 5) can be distinguished. This subassociation, dominated by microphyllous trees such as Cercidium praecox and Prosopis palmeri, indicates the presence of clay soils with phreatic water. The moister mountainous areas of the Magdalenense Sector support a related association to be described next. Mascagnio macropterae-Lysilometum candidae ass. nova; nomenclatural type: Table 11, rel. 4 The main dominant is the white-stemmed tree Lysiloma candida, which is known from two areas only: near Bahía San Pedro, Sonora, where it is found in some canyon bottoms, and in Baja California, where it occurs as a character species of the Mascagnio-Lysilometum. - Major plant communities of some warm North American deserts Table 11. Mascagnio macropterae-Lysilometum candidae ass. nova. Type relevé: 4, Rancho Ascensión, between Rosarito and El Bombeador, Baja California Sur, July 4, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 50 150 10 2 100 150 15 3 350 150 12 4 130 150 12 5 30 150 15 Mascagnio macropterae-Lysilometum candidae: Differentiating floristic combination Lysiloma candida 2 2 3 2 3 Bebbia • atriplicifolia * 2 1 2 . 1 Cercidium microphyllum 1 2 2 2 2 Mascagnia macroptera 1 + 2 1 1 Ruellia californica 1 2 2 1 1 Thermotropical taxa Hyptis decipiens * Viscainoa • pinnata Passiflora • longipedunculata Jatropha cinerea Dalea ♦ trochilina * Tephrosia palmeri Acacia peninsularis * Bursera epinnata Caesalpinia pannosa * Desmanthus fruticosus * Eucnide cordata Forchammeria watsonii Melochia tomentosa * Opuntia ciribe * Cissus trifoliata Ditaxis brandegeei Jacquemontia abutiloides Jatropha cuneata 2 . + . . . . . . . . . . . . . . . . 1 . . . . . . 1 1 1 . . . . . . . 2 . 2 . 2 2 . . . . . . . . . . + . . + . 1 . . . 1 . . . 1 . 1 . . . . . . . + . . 1 . . . . . 1 . + + . + Other taxa Zizyphus sonorensis Horsfordia newberryi Olneya tesota Encelia • farinosa Hymenoclea salsola . . . + + . 1 1 + + 2 1 . . . 2 . 2 . . . . . . . Additional taxa: Lemaireocereus thurberi (rel. 5: +), Lophocereus schottii (5: +), Pachycereus pringlei (4: +), Petalonyx linearis (1: +), Phytolacca octandra (2: +), Prosopis articulata (2: 1), Sapium biloculare (5: 2). The association thrives on mountain slopes of the Sierra de la Giganta, which form part of the Magdalenense Sector. It occurs above the Euphorbio-Fouquierietum, which grows on alluvial plains. A striking feature of this association is the absence of numerous desert taxa, owing to the orographic increase in precipitation, as well as to the influence of the tropical thornscrub of the adjacent Sanlucana Province (Peinado et al. 1994a). Bursero microphyllae-Cyrtocarpetum edulis ass. nova; nomenclatural type: Table 12, relevé 6 This association is composed of drought-deciduous, often thorny, pinnate-leaved, multi-trunk trees and shrubs from 2 - 7 m in height. The absence or poor representation of many characteristic desert species in part of the relevés, i.e. the ubiquitous Larrea tridentata, is also noteworthy. However, some of those taxa appear in a subassociation larreetosum tridentatae (subass. nova; nomenclatural type: Table 12, rel. 8), which indicates the northern transition to the Euphorbio californicaeFouquierietum diguetii from the Magdalenense Sector. Biogeographically, the association forms part of the 89 Table 12. Bursero microphyllae-Cyrtocarpetum edulis ass. nova. Type relevés: association, rel. 6: 4 km S of Las Cabrillas, July 7, 1992; subassociation larreetosum tridentatae, rel. 10: Near San Agustín, July 9, 1992. Both in Baja California Sur. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 2 3 4 5 6 7 8 9 10 50 410 230 130 10 20 50 240 210 150 150 150 150 150 150 150 150 150 150 150 27 26 19 24 21 22 20 23 28 14 Bursero microphyllae-Cyrtocarpetum edulis: Differentiating floristic combination Cyrtocarpa edulis * 2 2 2 2 2 2 2 1 2 2 Ruellia peninsularis 2 2 2 2 1 2 1 1 1 . Antigonum leptopus 1 1 + + 1 1 + . . . Aeschynomene nivea * + + + 1 1 1 + . . . Cnidoscolus angustidens 1 + 1 . . 1 1 + . . Bursera cerasifolia* + . . 1 + + . . + . Melochia tomentosa * . . + . . + 1 + + . Bursero microphyllae-Cyrtocarpetum edulis larreetosum tridentatae Larrea tridentata . . . . . . . 1 Gossypium harknessii * . . . . . . . 2 Citharexylum flabellifolium . . . . . . . 1 Hibiscus denudatus . . . . . . . 1 1 1 + 1 1 . + . Thermotropical taxa Bursera microphylla Opuntia ciribe * Fouquieria diguetii Jatropha cinerea Bursera odorata Euphorbia • californica Yucca valida Bourreria sonorae Viguiera tomentosa Ferocactus • towsendianus * Jatropha cuneata Mammillaria capensis * Opuntia • nuda * Merremia aurea * Haematoxylon brasiletto Cochemia poselgeri * Lysiloma candida Plumeria acutifolia Berginia • glandulifera * Cercidium ♦ peninsulare * Gochnatia arborescens Agave aurea * Agave • datylio * Castela peninsularis * Condalia globosa Erythrina flabelliformis Forchammeria watsonii Mammillaria hutchinsoniana * Pereskiopsis porteri Other taxa Machaerocereus gummosus Pachycereus pringlei Lemaireocereus thurberi Pedilanthus macrocarpus Krameria • parvifolia 2 1 1 2 2 . . 1 + . 1 . . . 1 + + . 1 + . . 1 + . . 1 . 2 + 2 1 . . . . 2 + . . + 1 . + . 1 . . 1 + . . . 1 . . + 2 1 2 2 . 1 + . 1 . . . . . . . . + . + . . . . . 1 . . + 2 1 1 1 1 1 1 . + . . 1 + . . . . . . . . + + . . . . 1 . 2 1 2 . . + . + . . 2 1 + + 2 . . . . . . . . + . . . . . 2 2 2 2 2 . 1 1 . . . . . . 1 . . . . . . . . 1 . . . . . 2 1 2 2 + 1 + 1 . . . . . 2 . . . . . . 1 . . . . . . . . 2 1 2 2 . + 1 . . 1 + . . . . . . . . . . . . . . . + . . 2 1 + + 1 . . + . + 2 1 . . . + 1 . + . . . . . + . + . . 1 1 2 1 . . . . . 1 . + . . . . . . . . . . . . . . . . . + 1 + . r 1 1 . . . 1 1 . . . 1 1 1 1 . 1 + 1 . r 1 1 1 1 . 1 + + . . 1 1 + 1 . 1 + + 1 . 1 1 1 + . Additional thermotropical taxa: Acacia cymbispina (rel. 2: 2), Atamisquea marginata (10: r), Bursera epinnata (9: 1), Cercidium praecox (1: +), Cissus trifoliata (2: +), Coursetia glandulosa (2: 2), Lycium berlandieri (9: 1), Mammillaria evermanniana * (4: 1), Opuntia bravoana (2: 1), Pachycereus pecten-aboriginum (7: 1), Phoradendron diguetianum * (6: +), Prosopis palmeri * (8: r), Tecoma stans (2: 1), Tillandsia recurvata (8: r). Other taxa: Lophocereus schottii (2: 1), Opuntia tesajo * (4: r), Simmondsia chinensis (5: 1), Solanum hindsianum (6: 1). thermotropical belt of the Sanlucana Province, which is floristically connected to the Caribbean Region (Takhtajan 1986). The most representative type of vegetation in the lowlands of this Province has close physiognomical relationships with the Sinaloan thornscrub (Shreve & Wiggins 1964; Brown 1982). 90 Peinado, M. et al. Table 13. Opuntio basilaris-Larreetum tridentatae ass. nova. Type relevé: 1, Twenty Mules Team Canyon Death Valley (California), June 3, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 2 3 4 5 6 7 170 950 850 700 660 690 1120 100 100 100 50 50 100 100 6 7 12 7 6 11 10 8 9 10 300 900 800 100 100 100 6 13 12 Opuntio basilaris-Larreetum tridentatae: Differentiating floristic combination Opuntia basilaris 1 1 1 1 1 + 1 1 + + Ambrosia dumosa 1 2 1 1 1 1 2 1 2 2 Larrea tridentata 2 2 1 1 1 1 1 1 1 2 Eriogonum inflatum . 1 1 + . 1 1 1 1 . Other taxa Opuntia • echinocarpa Stephanomeria pauciflora Atriplex hymenelytra Dalea fremontii Hymenoclea salsola Lycium andersonii Mirabilis froebelii Amphipappus ♦ fremontii Atriplex confertifolia Encelia ♦ actoni Yucca schidigera Echinocactus polycephalus Viguiera reticulata Bebbia • juncea Krameria • imparata Peucephyllum schottii . 1 . . 2 . . . . . . . . . . 2 1 + . . . . . . . . . . . . . 1 + . . + . . . . . . 1 . . . 1 . + . 1 . . . . . . . . + . . . . + + + . . . . . . . . . . . . . . 1 . 1 + . + . . 1 . . 1 1 . . . + . 2 . 2 1 + 1 . . . . . . . + . + . . . . . . . . . . . . . . . + . . + . 1 + + . 2 + . . . + . . . 2 . . . . . 1 . . + + . Additional taxa: Croton • mohavensis (rel. 1: +), Cuscuta denticulata (3: +), Dyssodia porophylloides (10: 2), Ephedra funerea (9: 2), Ephedra nevadensis (9: 2), Eriogonum elongatum (10: 2), Eriogonum ♦ polifolium (10: 2), Hilaria rigida (3: +), Lycium oligospermum (8: 2), Neolloydia johnsonii (3: +), Opuntia • acanthocarpa (10: 1). locally named mangrove, this community has no ecological relation with the tidal mangrove vegetation. The roots of Maytenus phyllantoides do not tolerate flooding. The plant receives moisture by condensation of marine air and fog on its leaves (Delgadillo et al. 1992). The association occurs in the coastal strip of thermotropical Baja California. Opuntio basilaris-Larreetum tridentatae ass. nova; nomenclatural type: Table 13, rel. 1 The association is physiognomically dominated by Larrea tridentata and Ambrosia dumosa, as is the Fouquierio splendentis-Larreetum tridentatae, but the presence of Opuntia basilaris and the absence of Fouquieria splendens are differentiating features towards the Fouquierio-Larreetum. Creosote-bush scrub dominates 70 % of the Mojave Desert (Shreve 1942) and most of this shrubland corresponds to the Opuntio basilaris-Larreetum tridentatae, which is the characteristic association of the lower bajadas and plains in the lowlands of the Mojave Province and neighbouring areas of the Colorada Province. Acamptopappo sphaerocephali-Larreetum tridentatae ass. nova; Nomenclatural type: Table 14, rel. 3 This association is related to the former one but is clearly differentiated from it by the dominance of shrubs such as Cassia armata, Thamnosma montana, Tetradymia axillaris, Ephedra nevadensis, Acamptopappus Table 14. Acamptopappo sphaerocephali-Larreetum tridentatae ass. nova. Type relevés: Type of the association, relevé 3: between Needles and Goffs, Piute Mountains, San Bernardino Co., California, May 31, 1992; type of the subassociation coleogynetosum ramosissimae, relevé 7: Emigrant Canyon, Death Valley National Monument, Inyo Co., California, June 2, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 900 2 3 4 5 6 7 8 9 10 750 1050 1150 1310 1250 1210 1500 1200 1150 100 100 100 100 100 100 100 100 100 100 13 18 19 23 18 23 16 17 11 18 Acamptopappo sphaerocephali-Larreetum tridentatae: Differentiating floristic combination Acamptopappus sphaerocephalus 1 2 2 1 + . + . 2 2 Larrea tridentata 2 2 1 1 1 1 . . 1 + Lycium andersonii 1 . . 1 1 + 2 2 2 + Salazaria mexicana . 2 . + 1 2 2 + 2 + Ephedra nevadensis . . . + 1 1 2 2 2 2 Tetradymia axillaris . . 2 + . . 2 2 . 1 Yucca brevifolia . . . 1 . 1 . + . + Menodora spinescens . . . . . 1 . . 2 1 Thamnosma montana . . 1 . . 2 2 . . . Acamptopappo sphaerocephali-Larreetum tridentatae coleogynetosum ramosissimae Coleogyne ramosissima . . . . . 2 2 2 . . Grayia spinosa . . . . . 2 2 2 2 . Xylorrhiza tortifolia . . . . . . 1 2 . . Acamptopappo sphaerocephali-Larreetum tridentatae variant of A. shockleyi Acamptopappus shockleyi . . . . . 2 2 2 . . Acamptopappo sphaerocephali-Larreetum tridentatae variant of Eurotia lanata Eurotia lanata . . . + 2 + . + . 1 Psilostrophe cooperi . . . + 2 . . . . . Other taxa Hymenoclea salsola Eriogonum inflatum Ambrosia dumosa Eriogonum ♦ polifolium Hilaria rigida Yucca schidigera Haplopappus cooperi Baileya multirradiata Krameria • imparata Oryzopsis hymenioides Lycium cooperi Acacia greggii Krameria grayi Lepidium fremontii Opuntia • acanthocarpa Dalea fremontii Stephanomeria pauciflora Atriplex confertifolia Atriplex ♦ linearis Mirabilis froebelii Mirabilis tenuiloba Opuntia • echinocarpa Opuntia polyacantha Opuntia ramosissima Porophyllum gracile Salvia dorryi Stipa speciosa Yucca baccata . 1 . + 1 + . + . . . + 1 . . . . . . . . . . . . . . . . + 2 1 1 1 . + + . . + + . + . + . . . . . . + + . . . + . 1 2 + 1 1 . . . . 1 2 . 2 . + . . . 1 . 2 1 + . . 1 + . + 1 1 2 . + + 1 . . . 1 . . . . . + . + . . + . + 1 + . . 1 . 1 + 1 1 1 . . . . . . . + . . . . . . . 1 2 + + 1 1 . 1 . + + + . . . . . 2 . . . . . + . . . + . . . . . . . . . . . + . . . + . + . + . + . . . . . . . . . . . . . . 2 . . . . . . + . 2 . . . + . . . . . . 1 . 2 1 1 . . . . . . . . . . . . . 1 . . . . . . . . . . . 2 . 1 . . . . . . 2 . . 1 . . . 1 2 . . + . . . . . . Additional species: Aristida fendleriana, (rel. 1:1), Artemisia spinescens (8:1), Artemisia tridentata (10:2), Atriplex polycarpa (10:2), Cassia harmata (2:1), Condaliopsis lycioides (1:1), Dyssodia cooperi (2:1), Echinocereus engelmannii (3:+), Echinocereus mojavensis (6:+), Ephedra viridis (1:1), Haplopappus sonorensis (7:+), Stanleya elata (8:+). Maytenetum phyllanthoidis ass. nova; nomenclatural type: Delgadillo et al. 1992, Table 16, rel. 2 This association is almost exclusively dominated by Maytenus phyllanthoides, accompanied by the halophilous Lycium andersonii. The Maytenetum phyllanthoidis is a community with a narrow range, which occurs on sea-exposed slopes with an immediate influence of salt spray. Although Maytenus phyllanthoides is - Major plant communities of some warm North American deserts - 91 Table 15. Fouquierio splendentis-Larreetum tridentatae ass. nova. Type relevé: rel. 3: 38 km north of Mexicali, Baja California, April 23, 1989. Symbols as in Table 2. Table 16. Echinocereo engelmannii-Agavetum deserti ass. nova. Type relevé: 4, San Felipe Creek, Anza Borrego, San Diego County, California, May 8, 1991. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa No. of relevé Altitude (m) Area (m2) No. of taxa 1 2 3 4 5 6 7 8 9 10 20 30 180 80 560 90 560 600 250 700 200 50 200 100 100 100 100 100 100 100 4 4 6 5 8 4 4 8 6 8 Fouquierio splendentis-Larreetum tion Fouquieria splendens 2 Larrea tridentata 2 Ambrosia dumosa 2 Other taxa Opuntia • acanthocarpa Encelia • farinosa Simmondsia chinensis Opuntia • echinocarpa Hilaria rigida Eriogonum ♦ flavoviride . . . . . . tridentatae: Differentiating floristic combina1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 2 1 1 1 1 1 1 1 + . . . . . + 2 . 1 . . 1 1 . . . . + . + 1 . + . . . + . . . . 1 . . . 1 . 2 . . 1 + . . . 1 . . 1 . . 1 . Additional species: Hyptis • emoryi (rel. 10: 1), Krameria grayi (1: +), Krameria • imparata (9: +), Lophocereus schottii (5: +), Lycium andersonii (10: +), Opuntia littoralis (8: +), Trixis californica (10: 1), Yucca schidigera (8: 1). sphaerocephalus, A. shockleyi and several species of Krameria and Eriogonum. Yucca brevifolia (Joshua tree) is the best-known species of this association; however, this Mojavean endemic can also be found in many other plant communities (Rowlands 1978). This is a widespread association in the highlands of the mesotropical belt of the Mojave Province, replacing the Opuntio basilaris-Larreetum tridentatae in desert mesas and slopes at altitudes between 900 and 1500 m. The subassociation coleogynetosum ramosissimae (subass. nova, nomenclatural type: Table 14, rel. 7) is found in the transitional Mojave-Great Basin areas of the highest lands of the Mojave Desert. In some mountains of Inyo and San Bernardino counties (White and Clark Mountains) there is a floristic variant (rels. 6-8) in which the endemic Acamptopappus shockleyi replaces the more common A. sphaerocephalus. The variant of Eurotia lanata (rels. 4- 6 and 10) indicates soils with caliche layers. Fouquierio splendentis-Larreetum tridentatae ass. nova; nomenclatural type: Table 15, rel. 3 This association is characterized by Larrea tridentata, Fouquieria splendens and Ambrosia dumosa. Larrea tridentata is the dominant plant on loamy soils; on sandy soils, the dominance is shared with Ambrosia dumosa and the grass Hilaria rigida. The uniform stature and spacing of the plants and the floristic simplicity of the association produce a monotonous landscape that dominates plains and lower bajadas surrounding the mountains in the Colorada Province. It occurs in the Lower Colorado Valley, which is the largest and most arid subdivision of the Sonoran Desert (Turner & Brown 1982) and floristically the poorest part. In fact, this is the most widespread and important plant community in the 1 2 3 4 5 6 7 8 530 600 700 70 550 500 970 1100 100 100 100 100 100 100 100 100 15 14 16 19 17 17 17 13 9 740 100 16 10 710 100 19 Echinocereo engelmannii-Agavetum deserti: Differentiating floristic combination Echinocereus engelmanii + 1 + 1 1 1 1 + 1 + Agave ♦ deserti 2 2 2 2 1 1 2 . . . Ferocactus ß acanthodes + + 1 1 . + 1 1 1 1 Echinocereo engelmannii-Agavetum desertii variant of A. pringlei Agave ♦ pringlei . . . . . . . 2 2 2 Other taxa Ambrosia dumosa Fouquieria splendens Opuntia • acanthocarpa Encelia • farinosa Mammillaria dioica Simmondsia chinensis Mirabilis • aspera Opuntia bigelovii Larrea tridentata Krameria • imparata Yucca schidigera Opuntia • echinocarpa Ambrosia deltoidea Trixis californica Krameria grayi Ephedra aspera Hilaria rigida Viguiera • parishii Stephanomeria pauciflora Beloperone californica Eriogonum angulosum Thamnosma montana Opuntia basilaris Prunus fremontii Acalipha californica Aristida parishii Peucephyllum schottii Porophyllum gracile Lycium andersonii Bebbia • juncea Juniperus californica Ditaxis serrata Hibiscus denudatus Salvia mellifera Eriogonum inflatum 2 2 1 . + 2 . + . . . . . . + . . . . . . . . . . . 1 . . . + . . . . 2 2 2 2 . 2 . 1 2 . . . . 2 + . . . . 2 . . . . 1 1 . . . . . 2 1 . . 1 1 . 2 1 . . . . + . + 1 . . + . . . . . 1 . . . . . . . + . . . 1 + 2 2 . 2 . . . . . + . + 1 . . . . . . . . 1 . . . . . . . + . . + . + 1 . . 2 1 + . . . . . 1 2 1 + . + . . . . . . . . . + . . . . . . + . 1 1 1 . . . 1 . 2 . 2 . . . . 2 2 1 1 . 1 . . . . . . 1 2 . . + . . . 1 1 1 . + . 2 1 1 2 . . . . . 1 . 1 1 2 2 . 1 . . . . . + . . . . . . 1 1 1 2 + 1 1 1 1 2 . . . + . . . . + . . . 1 . . . . . . . . . . . . 1 . 1 . . 1 1 . . . 1 . . . . . 1 1 . . . . . 1 . . . + . . 1 . . . . . . 1 . . . 1 . . 1 1 . . . . . . . . . . . . 1 1 1 . . . . . . . . . Additional species: Acacia greggii (rel. 7: r), Agave utahensis (7: 1), Cercidium microphyllum (10: 2), Dudleya saxosa (4: 1), Ephedra californica (9: +), Ephedra nevadensis (7: 1), Eriogonum fasciculatum (3: +), Eriogonum flavoviride (9: 2), Galium angustifolium (7: 1), Hyptis • emoryi (6: 1), Lotus brevialatus (8: 1), Nolina palmeri (3: 1), Opuntia littoralis (9: 1), Opuntia phaeacantha (8: 1), Opuntia tesajo (10: 2), Sphaeralcea ambigua (4: +), Stipa speciosa (8: 1), Viguiera laciniata (2: +). region, occurring over many thousands of hectares in the wide valleys in the region. The Fouquierio Larreetum is similar in appearance to the geographically adjacent Opuntio basilarisLarreetum, which occurs in the Mojave Province, but it differs in the following way: (1) the absence of Opuntia basilaris; (2) the presence of Fouquieria splendens (3) the occurrence of a tetraploid form of Larrea tridentata in the Colorada Province vs. a hexaploid form in the Mojave (Yang 1970). In the Arizona Sector, a new subassociation can be described on the basis of the presence of the nearly endemic Ambrosia deltoidea. 92 Peinado, M. et al. Table 17. Tidestromio oblongifoliae-Atriplicetum hymenelytrae ass. nova. Type relevé: rel. 2, near Badwater, Death Valley, Inyo County, California, June 2, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 3 3 4 5 380 –50 0 920 0 50 50 50 50 50 4 3 2 1 3 6 10 50 2 7 8 9 10 10 200 –30 –10 50 100 50 50 4 3 3 3 Tidestromio oblongifoliae-Atriplicetum hymenelytrae: Differentiating floristic combination Atriplex hymenelytra 1 1 1 1 1 1 1 1 1 1 Tidestromia oblongifolia + 1 . . . 1 1 1 1 1 Other taxa Larrea tridentata . + . . . . + 1 + 1 Additional species: Bebbia • juncea (rel. 7:1), Dalea schottii (5:+), Echinocactus polycephalus (1:1), Euphorbia parishii (3:1), Opuntia • echinocarpa (1:+), Suaeda torreyana (5:1). Echinocereo engelmannii-Agavetum deserti ass.nova; nomenclatural type: Table 16, rel. 4 The most characteristic species of this association is the semi-succulent, leathery, thick-leaved shrub Agave deserti ssp. deserti. Other common plants are the barrelcactus Ferocactus acanthodes, as well as Echinocereus engelmannii, Fouquieria splendens several shrubs such as Encelia farinosa, Krameria imparata and Ambrosia dumosa. This mesotropical association grows on rocky upland slopes and piedmonts of desert mountains that surround the edges of the Colorada Province. In northeastern Baja California (Sanfelipense Sector), there is a floristical variant in which the endemic Agave deserti ssp. pringlei locally replaces ssp. deserti (rels. 8 - 10). Tidestromio oblongifoliae-Atriplicetum hymenelytrae ass. nova; nomenclatural type: Table 17, rel. 2 The two dominant species of this association are Tidestromia oblongifolia and Atriplex hymenelytra; they use dew to enhance their water status (Babu & Went 1978). This is an association that endures the most arid conditions of the North American deserts, with a precipitation of less than 50 mm/yr. It is found in the Death Valley and the San Felipe Desert (Mojave and Colorada Provinces) where it grows in open sparse stands on volcanic rocks, pavement soils and gravelly bajadas. Larrea tridentata and some cacti, such as Echinocactus polycephalus and Opuntia echinocarpa, are the only other species capable of enduring the extreme ecological conditions characteristic of this association. Cercidio microphylli-Carnegieetum giganteae ass. nova; nomenclatural type: Table 18, rel. 4 This a real association of species because it is based on the well-known interaction between Carnegiea gigantea (saguaro) and its nurse plant, the small tree Cercidium microphyllum (foothill paloverde) (Turner et al. 1966; Brum 1973; Steenbergh & Lowe 1977). This Table 18. Cercidio microphylli-Carnegieetum giganteae ass. nova.Type relevé: rel. 4, Brownell Mountain, Pima County, Arizona, July 12, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 2 3 4 5 6 7 8 9 10 450 550 580 750 780 770 400 580 600 580 200 200 200 200 200 200 100 100 100 100 7 11 14 14 16 16 8 9 10 9 Cercidio microphylli-Carnegieetum giganteae: Differentiating floristic tion Cercidium microphyllum 1 2 2 2 2 1 2 2 Carnegiea gigantea + 1 1 1 1 1 2 1 Ambrosia deltoidea 1 2 2 1 2 2 + 1 Opuntia fulgida . 1 1 + 1 + . . Acacia constricta . 1 1 2 + + . . Olneya tesota 1 + . . 2 1 . . Opuntia • thornberi . . + . + + 1 . Other taxa Larrea tridentata Fouquieria splendens Opuntia • discata Krameria • imparata Opuntia arbuscula Opuntia leptocaulis Ferocactus wislizeni Opuntia • echinocarpa Echinocereus nicholii Echinocereus fasciculatus Ferocactus covillei Mammillaria microcarpa Opuntia bigelovii Opuntia • tetracantha Opuntia versicolor Ambrosia dumosa 1 . . 1 . . . . . . . . . . . 1 1 1 . 2 . . . 1 . + . . . . . . 1 1 + 1 . . . 1 . 1 + . . . . . 1 . + . + + . . + . 1 . . . . . 1 1 1 + 1 + + . . . . + . + . . 1 1 + + 1 + + . . . . + . 2 . . 1 2 . . . . . . . . . . 1 . . . 2 1 1 . . . . 1 . . . . . . . + combina2 2 2 1 . . . 2 2 2 . . . . 2 1 . . . . + . + . . . . . 1 . 2 2 . . . . . . + . . . 1 . 1 . Additional species: Acacia greggii (rel. 4: 1), Encelia • farinosa (7: 1), Ephedra viridis (3: +), Lemaireocereus thurberi (10: +), Opuntia imbricata (8: 1), Opuntia • macrocentra (9: +), Prosopis velutina (4: 2), Psilostrophe cooperi (4: 1). mesotropical association also includes Olneya tesota (ironwood) and shrubs such as Larrea tridentata, Ambrosia deltoidea, A. dumosa and several cacti, some of them endemic or nearly endemic to Arizona, e.g. Opuntia fulgida and O. thornberi. It is the most widespread plant community in the Arizona Sector of the Colorada Province. The association occupies mountain slopes and upper bajadas above the Fouquierio splendentis-Larreetum tridentatae. Hymenocleo salsolae-Daleetum spinosae ass. nova; nomenclatural type: Table 19, rel. 4 This species-poor association is dominated by the small smoke tree Dalea spinosa that grows along periodically flooded water courses and on gravelly drainage ways subjected to sporadic and violent torrential rains and flash floods. It occurs in the Colorada Province. Prosopidetum torreyanae ass. nova; nomenclatural type: Table 20, rel. 4 This association has only one constant and dominant species, the small, microphyllous tree Prosopis glandulosa var. torreyana, a phreatophyte that inhabits sandy soils, mainly in dunes, where runoff water accumulates. Since this association indicates buried phreatic layers lying beneath plains and playas, it usually forms patches - Major plant communities of some warm North American deserts Table 19. Hymenocleo salsolae-Daleetum spinosae ass. nova. Type relevé: rel. 4, Rancho La Estrella, Desierto de San Felipe, Baja California, November 12, 1990. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 2 3 4 5 6 7 8 9 10 180 160 600 10 180 220 900 400 400 850 100 100 100 100 50 100 100 100 100 100 5 4 3 9 4 7 8 11 6 9 Hymenocleo salsolae-Daleetum spinosae: Differentiating floristic combination Dalea spinosa 2 2 3 3 3 3 3 3 2 2 Hymenoclea salsola 2 2 1 1 2 2 2 2 1 1 Other taxa Larrea tridentata Ambrosia dumosa Encelia• farinosa Petalonyx thurberi Prosopis • torreyana Cercidium ♦ floridum Isomeris arborea Hyptis • emoryi Viscainoa • geniculata Bebbia • juncea Phoradendron californicum Prosopis articulata Salvia mellifera Acacia greggii 1 . . . . 2 . . . . . . . . + . . . . + . . . . . . . . + . . . . . . . . . . . . . 1 1 . 1 + . . . . . . . + . . + 2 . . . . . . . . . . . . . + . . . . . . . . 2 1 . . . . 1 . . + 1 1 1 . . . + . . + 1 + . . 2 1 1 . . . + . 1 . . 2 . . . . . + . . . . . . . . . 1 . . . 1 . . . Additional species: Acalipha californica (rel. 7: 1), Atriplex polycarpa (1: +), Cercidium microphyllum (8: 2), Chilopsis linearis (9: +), Coldenia plicata (4: +), Cucurbita palmeri (4: +), Dalea fremontii (9: 1), Lycium andersonii (9: +), Lycium cooperi (9: +), Opuntia • echinocarpa (9: +), Palafoxia linearis (6: 1), Solanum hindsianum (7: +), Tamarix aphylla (6: +). 93 Table 20. Prosopidetum torreyanae ass. nova. Type relevé: rel. 4, Valle de la Trinidad, Baja California, November 11, 1990. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 2 3 4 5 770 650 750 740 20 100 100 100 100 50 8 2 1 3 6 6 10 50 2 7 8 9 10 740 0 50 100 50 6 1 1 10 0 50 7 Prosopidetum torreyanae: Differentiating floristic combination Prosopis • torreyana 3 4 4 4 4 4 3 5 5 3 Other taxa Distichlis spicata Phoradendron californicum Larrea tridentata Lycium cooperi Suaeda torreyana Atriplex ♦ canescens Haplopappus tridentatus Gutierrezia bracteata . . . . . . . . . . . . . . . . + 1 . + + 1 1 . 1 1 . 1 1 1 1 . + . . . . . . . . . . . . . . . . . 1 . . . . . 1 . . + + 1 . 1 . . . . . . . . . 1 1 . . . . . Additional species: Beloperone californica (rel. 6: 1), Atriplex polycarpa (6: 1), Adolphia californica (7: 1), Hymenoclea salsola (1: +), Lycium andersonii (7: +), Krameria grayi (4: r). Table 21. Hymenocleo monogyrae-Baccharidetum glutinosae ass. nova. Type relevé: rel. 6, Arroyo El Rosario, Baja California, May 20, 1992. Symbols as in Table 2. Relevé no. Altitude (m) Area (m2) No. of taxa 1 520 10 4 2 780 20 4 3 260 50 4 4 200 50 6 5 6 7 220 15 250 50 50 40 6 8 7 Hymenocleo monogyrae-Baccharidetum glutinosae: Differentiating floristic combination Hymenoclea monogyra 1 3 4 3 1 3 3 Baccharis glutinosa 3 . 1 1 3 1 1 Tamarix pentandra + . 1 1 . 1 1 Nicotiana glauca . . 1 . . 1 1 in areas dominated by other different associations such as the Opuntio basilaris-Larreetum tridentatae and Fouquierio splendentis-Larreetum tridentatae. The association occurs in mesotropical desert areas, especially in the Colorada Province. Hymenocleo monogyrae-Baccharidetum glutinosae ass. nova; nomenclatural type: Table 21, rel. 6 This is a riparian shrubland association mainly characterized by the two species occurring in the name. It occupies the margins and riverbeds of some rivers and water courses in transitional mediterranean-desert areas of northern Baja California, i.e. the thermomediterranean and infra-mediterranean belts of the Martirense Province and the mesotropical belt of the Vizcaíno Sector. The Mediterranean tree Tamarix pentandra is common in this association and it is ecologically similar to the Mediterranean riparian shrubland. Acknowledgements. This work has been supported with grants from the Consejería de Educación de la Comunidad de Madrid, Subdirección General de Promoción de la Investigación del Ministerio de Educación y Ciencia and DGICYT (Research Project PB90-0293). We thank C. F. Warren for her linguistic assistance. We also thank two anonymous referees for comments that improved this paper. Part of the research was carried out during a four-month stay at Rancho Santa Ana Botanic Garden. 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