286 PrOCeedINgS OF THe CALIFOrNIA ACAdeMy OF SCIeNCeS Series 4, Volume 63, No. 8 munity and, thus, feature many of the same species including: Ambrosia dumosa, Ephedra aspera, Eriogonum fasciculatum, Hilaria rigida, Jarava speciosa, Krameria erecta, and Larrea tridentata. with sufficient late winter rains, a high diversity of winter ephemerals are found in the Low-gradient desert wash Scrub, many of which are listed above in the description of the Mohave desertscrub Biome. Sacramento wash is the largest low-gradient drainage near the southern Black Mountains, has multiple channels, and forms the southeastern boundary of the flora area for approximately 32 km (20 mi). The Low-gradient desert wash Scrub here is dominated by Ambrosia monogyra, Baccharis salisifolia, Parkinsonia microphylla, Psorothamnus spinosus,and Senegalia greggii, with an herbaceous stratum consisting of Cryptantha decipiens, Cryptantha micrantha, Descurainea pinnata, Pectocarya platycarpa, Pectocarya recurvata, Senecio flaccidus, and Stillingia linearifolia. The sand substrate provides suitable habitat for several species not found elsewhere in the flora area including Baileya pleniradiata, Brickellia incana, Cryptantha circumscissa, Dimorphocarpa wislizenii, Oenothera deltoides subsp. deltoides, Palafoxia arida, and Tiquilia plicata. An undetermined species of what appears to pertain to Petalonyx (Daniel & Butterwick 6042) has leaves with a dense pubescence of soft, white, and flexuose hairs, unlike the scabrous herbage of Petalonyx nitidus, which occurs elsewhere in the flora area. Upstream reaches of these tributaries, generally over 914 m (3000 ft) in elevation, are highgradient (generally >3%) streams often with cobble, boulder, or bedrock substrates and steep side slopes that in places narrow into canyons. The relatively cooler and moister conditions at these sites support a more species-rich variant of desert wash Scrub, referred to here as High-gradient desert wash Scrub, and they include several woodland and chaparral species (Fig. 11). we observed this plant community in several tributaries north of Mohave Co. 10 (Oatman road). In this community species collected on canyon bottoms or adjacent slopes include: Acamptopappus sphaerocephalus, Amsonia palmeri, Artemisia ludoviciana, Baccharis sergiloides, Bothriochloa barbinodis, Eucnide urens, Forestiera pubescens, Fraxinus anomala, Hyptis emoryi, Keckiella antirrhinoides, Melica imperfecta, Nolina bigelovii, Quercus turbinella, Rhamnus ilicifolia, and Salvia mohavensis. In shaded crevices of the canyon walls are found Brickellia atractyloides, Cheilanthes parryi, Crossosoma bigelovii, Erigeron oxyphyllus, Ivesia arizonica, Pellaea truncata, Perityle emoryi, Phacelia perityloides, Phacelia rotundifolia, Phacelia saxicola, Pleurocoronis pluriseta, and Pterostegia drymarioides. Among these, Erigeron oxyphyllus, Ivesia arizonica, Phacelia perityloides, Phacelia rotundifolia, and Phacelia saxicola are apparently rare, and thus far each one has been documented from a single locale in the flora area. WETLANDS.—year-round sources of water are restricted to perennial springs that occur on slopes, in narrow and boulder-strewn canyons, or in the more open, sand and gravel beds of tributaries at lower elevations. Of the 23 springs we sampled, the linear extent of surface and shallow subsurface flows varies from approximately 0.8 km (0.5 mi), at Cool Spring, to the immediate vicinity of the spring itself. The more extensive springs support a desert Oasis woodland plant community with a tree and shrub stratum (Fig. 11) and/or a Streamside Marsh plant community comprised of herbaceous species along the wet streambed and banks (Fig. 11). Several springs with limited flows support very little distinct vegetation, often consisting of single trees, such as Prosopis glandulosa var. torreyana at Metate Spring and Celtis reticulata at whiskey Spring. In total, the vegetation associated with these perennial springs covers a very small area within this arid landscape and, consequently, many of the species associated with these plant communities are rare in the flora area. The desert Oasis woodland is dominated by the following trees: Celtis reticulata, Parkinsonia florida, Populus fremontii, Prosopis glandulosa var. torreyana, Prosopis pubescens, Quercus
BUTTerwICK & dANIeL: FLOrA OF SOUTHerN BLACK MTS., ArIzONA 287 turbinella, and Salix gooddingii. Common shrub species include Ambrosia monogyra, Baccharis salicifolia, Baccharis sergiloides, Salix exigua, and Pluchea sericea. The Streamside Marsh may occur as an herbaceous stratum of the desert Oasis woodland or alone in more open drainages such as the series of step pools at Columbine Spring (Fig. 11). Species characteristic of the Streamside Marsh are numerous and include: Adiantum capillis-veneris, Polypogon viridis, Apocynum cannabinum, Aquilegia chrysantha, Carex alma, Castilleja minor subsp. spiralis, Chenopodium berlandieri, Cyperus laevigatus, Eleocharis ovata, Eleocharis parishii, Eleocharis rostellata, Pseudognaphalium luteoalbum, Heliotropium curassavicum, Juncus acutus, Juncus bufonius, Juncus ensifolius, Lythrum californicum, Mimulus guttatus, Mimulus verbenaceus, Muhlenbergia rigens, Nasturtium officinale, Paspalum dilatatum, Petunia parviflora, Phragmites australis, Polypogon interruptus, Polypogon monspeliensis, Rumex hymenosepalus, Solanum americanum, Spergularia marina, Typha latifolia, Veronica anagallis-aquatica, Vitis arizonica, and Wislizenia refracta (Fig. 12). A few of the herbaceous wetland species are currently known from a single spring. For instance, Columbine Spring, near the headwaters of an ephemeral tributary to warm Springs wash, has the only documented occurrence of Sisyrinchium demissum and Zeltnera arizonica (Fig. 12) in the flora area. Two grass species, Andropogon glomeratus and Imperata brevifolia, have been documented only from Cottonwood Spring in Cottonwood Canyon in the southern Black Mountains.
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