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280 PrOCeedINgS OF THe CALIFOrNIA ACAdeMy OF SCIeNCeS<br />
Series 4, Volume 63, No. 8<br />
bergia fragilis, and Pectis papposa. Six species of ephemeral herbs flower throughout the year in<br />
response to rainfall: Aristida adscensionis, Baileya pleniradiata, Chamaesyce setiloba, Conyza<br />
canadensis, Eriogonum hookeri, and Eriogonum palmerianum.<br />
CREOSOTE BUSH SCRUB.—This plant community (Fig. 7) is generally comparable to the Creosotebush<br />
Series of Brown et al. (1979) and Turner (1982). It occurs on the lower hills, upper and<br />
lower bajadas, and valley basins (generally between 335 m (1100 ft) and 914 m (3000 ft) elevation),<br />
from the base of the mountains toward Sacramento wash on the south and east sides of the<br />
flora area and toward the Colorado river on the west side of the flora area. The dominant species<br />
Ambrosia dumosa, Encelia farinosa, and Larrea tridentata are characteristic of this plant community.<br />
Common associates include: Cylindropuntia acanthocarpa, Cylindropuntia bigelovii,<br />
Ephedra aspera, Fouquieria splendens, Krameria erecta, Opuntia basilaris, Psorothamnus fremontii,<br />
and Sphaeralcea ambigua (Figs. 4, 6, 8). ephemeral species can be abundant in response<br />
to rainfall. They include: Acmispon rigidus, Acmispon maritimus, Acmispon strigosus, Amsinckia<br />
intermedia, Amsinckia tessellata, Atrichoseris platyphylla, Bouteloua barbata, Bouteloua aristidoides,<br />
Chylismia brevipes, Chylismia claviformis, Chaenactis carphoclinia, Chaenactis fremontii,<br />
Chamaesyce arizonica, Chamaesyce melanadenia, Chamaesyce polycarpa, Chorizanthe brevicornu,<br />
Chorizanthe rigida, Cryptantha barbigera, Cryptantha maritima, Cryptantha pterocarya,<br />
Cryptantha utahensis, Eremothera refracta, Eriastrum diffusum, Eriastrum eremicum, Eriogonum<br />
deflexum, Eriogonum inflatum, Eriogonum thomasii, Eriogonum trichopes, Eriophyllum lanosum,<br />
Eschscholzia californica, Eschscholzia glyptosperma, Eschscholzia minutiflora, Gilia scopulorum,<br />
Gilia stellata, Langloisia setosissima, Linanthus bigelovii, Linanthus demissus, Lupinus concinnus,<br />
Malacothrix glabrata, Mentzelia albicaulis, Mentzelia involucrata, Monoptilon bellioides, Nama<br />
demissa, Nemacladus orientalis, Pectocarya platycarpa, Pectocarya recurvata, Phacelia crenulata,<br />
Phacelia distans, Plantago ovata, Rafinesquia californica, Rafinesquia neomexicana,<br />
Stephanomeria pauciflora, Syntrichopappus fremontii, and Vulpia octoflora.<br />
MIXED DESERT SCRUB.—Mixed desert Scrub dominates the upper mountain slopes and rock<br />
outcrops (generally between 850 m (2800 ft) and 1370 m (4500 ft) elevation) and features a greater<br />
diversity of species than Creosote Bush Scrub. This catch-all plant community (Fig. 2) occurs<br />
throughout much of the flora area and exhibits various combinations of associated species. Several<br />
of the desert growth forms are represented including: stem-succulent cacti (Fig. 8) such as Cylindropuntia<br />
echinocarpa, Echinocereus coccineus, Echinocereus engelmannii, Echinomastus johnsonii,<br />
Ferocactus cylindraceus, Mammillaria grahamii, Mammillaria tetrancistra, Opuntia<br />
chlorotica, Opuntia ×curvospina, and Opuntia polyacantha; leaf semisucculents like Agave mckelveyana,<br />
Nolina bigelovii, Yucca baccata, and Yucca schidigera (Figs. 3, 5); leaf-succulents (i.e.,<br />
Dudleya arizonica; Fig. 4); shrubby, often microphyllous, species, such as Brickella atractyloides,<br />
Brickellia incana, Encelia resinifera, Encelia virginensis, Ephedra aspera, Ericameria laricifolia,<br />
Ericameria linearifolia, Eriogonum fasciculatum, Eriogonum heermannii, Gutierrezia sarothrae,<br />
Keckiella antirrhinoides, Salvia dorrii, Salvia mohavensis, Thamnosma montana, and Xylorhiza<br />
tortifolia (Figs. 6, 9); subshrubs and perennial herbs, such as Acmispon rigidus, Artemisia ludoviciana,<br />
Baccharis brachyphylla, Boechera perennans, Cryptantha racemosa, Mirabilis laevis,<br />
Mirabilis multiflora, Nicotiana obtusifolia, Penstemon eatonii, Physalis crassifolia, Pleurocoronis<br />
pluriseta, Porophyllum gracile, and Peucephyllum schottii; perennial grasses including<br />
Acnatherum coronatum, Acnatherum hymenoides, Aristida purpurea, Bothriochloa barbinodis,<br />
Bouteloua curtipendula, Hilaria rigida, Jarava speciosa, Melica frutescens, Melica imperfecta,<br />
Muhlenbergia porteri, and Poa fendleriana; and numerous ephemerals, many of which are listed<br />
above. In more mesic sites on north-facing slopes and at the base of cliff faces at higher elevations<br />
are found species characteristic of woodland and chaparral plant communities, including: Ceanoth-