December 2012 Number 1 - Utah Native Plant Society

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Taxon Utah Native Plant Society Table 1. continued No. of Pop’s a Life Form b Habitat(s) Boechera falcifructa (Rollins) Al-Shehbaz 9 pf Zonal soils with big sagebrush zone Mentzelia argillicola N.H. Holmgren & P.K. Holmgren 5 pf Alkaline clays/silts of Pliocene lake beds Frasera gypsicola (Barneby) D.M. Post 10 pf Alkaline clays/silts of Pliocene lake bed; spring mounds Mentzelia tiehmii N.H. Holmgren & P.K. Holmgren 7 pf Alkaline clays/silts of Pliocene lake beds Eriogonum argophyllum Reveal 1 an Siliceous geothermal sinter Sclerocactus blainei S.L. Welsh & Thorne 3 ps Alkaline volcanic and calcareous clay soils Mimulus ”ovatus” c 9 pf Sandy to gravelly flats and slopes Eriogonum ovalifolium Nutt. var. williamsiae Reveal Eriogonum diatomaceum Reveal, J. Reynolds & Picciani 1 pf Siliceous geothermal sinter 11 pf Diatomaceous earth deposits Potentilla basaltica Tiehm & Ertter 9 pf Moist alkaline meadows a Number of reported populations in Nevada included in study; populations outside of Nevada included are shown in parentheses. b pf = perennial forb; ge = geophyte; an = annual; ps = perennial succulent. C Recent taxonomic revisions have left this western Nevada endemic, formerly included in Mimulus ovatus, without a name. well-documented in the White Mountains of California and Nevada (Marchand 1973; Mooney 1966; Mooney et al. 1962; Morefield 1992; Wright and Mooney 1965) and on altered andesites in western Nevada (Billings 1950). In an analysis of plant distributions in the Mojave-Intermountain transition zone, Meyer (1978) found that endemic plants showed a high degree of habitat specialization and that edaphically restricted species were much better represented in xeric, than in mesic, community types. Kruckeberg and Rabinowitz (1986) also provided case histories of Astragalus phoenix and Mentzelia leucophylla, both narrow edaphic endemics known from flats, washes, and knolls of calcareous alkaline soils at Ash Meadows National Wildlife Refuge in Nye County, Nevada. Ash Meadows lies on the periphery of, and shares many ecological features with, the adjacent Great Basin; paleosoils on which these two species occur are the partially dissected remnants of a large Pleistocene playa. Numerous examples also exist of endemism or rarity in Great Basin plants associated with soils derived from volcanic ash (Grimes 1984), sand dunes (Holm- gren 1979; Pavlik 1989a), geothermal features (Holmgren 1972b; Reveal 1972, 1981), Pliocene and Pleistocene lake and playa sediments, including gypsum mounds, (Forbis 2007; Holmgren and Holmgren 2002; Reveal 1972), diatomaceous earth deposits (Reveal et al. 2002), and pumice deposits (Reveal 2004a). A detailed discussion of examples of edaphic endemism among the rarest plants of the valley, montane, and high elevation habitats of the study area is presented in subsequent sections. In most cases, the specialized habitats of these taxa are more properly characterized as a substrate rather than a well-developed soil. Sand deposits, shallow gravel sinters, pumice fields, and volcanic ash exposures in the valleys and the scree and talus slopes of the mountains are typically dynamic, unstable substrates shaped by erosional processes. Mineral material dominates the soil profile, little organic material is present, and soil horizons are poorly differentiated, if they are even present. In a few cases, such as paleosoils developed on ancient lake beds, moist alkaline clays, or playa edges, the soils are better developed, although in the 96
case of the former lake beds a duripan is common within a short distance of the surface and the surface itself may be armored with desert pavement. The marked aridity of the Great Basin also slows the rate of soil development. While the degree of soil development has a substantial influence on the floristic composition and structure of more common, widespread plant communities, it appears to be less important in specialized edaphic endemics. In these habitats, physical soil factors (or perhaps, in some cases, soil chemistry) may have greater influence on the ability of species to establish and persist. Valley Endemics The 14 rarest plants below 2000 m all occur on valley floors within a matrix of zonal vegetation dominated by Artemisia tridentata ssp. wyomingensis or various salt desert shrubs (Figure 2, Table 1). Most occur on azonal soils developed from surficial deposits that overlie the underlying bedrock, in some cases by thousands of meters (Table 1). Eriogonum diatomaceum, for example, is restricted to diatomaceous earth deposits (Reveal et al. 2002). Mentzelia argillicola, M. tiehmii, and Frasera gypsicola are typically found on sediments comprised of calcareous silts, clays, and air-deposited ash beds that accumulated in Middle Pliocene-Early Pleistocene lakes (Tschanz and Pampeyan 1970), although the latter two species also occur on Pliocene spring mounds with high gypsum content (Forbis 2007). Frasera gypsicola is also rarely found in saline bottomlands (Smith 1994). Johanneshowellia crateriorum is known only from sandy pumice flats and slopes (Reveal 2004a) associated with the Quaternary Lunar Crater volcanic field (Kleinhampl and Ziony 1985). The habitats of Sclerocactus blainei and Mimulus ovatus have been described as igneous or calcareous gravels with a clay matrix (Heil and Porter 1994; Welsh and Thorne 1985) and sandy to gravelly slopes derived from siliceous sinter or hydrothermally-altered andesite (Morefield 2001), respectively. Eriogonum argophyllum, E. ovalifolium var. williamsiae, and Castilleja salsuginosa are all associated with geothermal features, either growing in siliceous sinter gravels (Erigonum spp.), or in moist alkaline clays or weathered travertine (Castilleja) (Holmgren 1972b; Reveal 1972, 1981). Potentilla basaltica is also restricted to alkaline wet meadows (Tiehm and Ertter 1984). The remaining low elevation species do not fit the same pattern of adaptation to azonal soils in the valleys. Boechera falcifructa appears to be the only lower elevation species that occurs on zonal soils; the association of known populations with cryptogammic soils crusts within the Artemisia tridentata ssp. wyomingensis zone suggests that it may once have been more widely distributed but subsequently reduced by livestock tramp- Calochortiana December 2012 Number 1 97 ling (Morefield 1997). The only plant among the lowest elevation group to grow only on soils directly weathered from bedrock is Eriogonum tiehmii, which occurs on rocky clay soils derived from interbedded sedimentary rocks, including claystones, shales, tuffaceous sandstones and limestones (Morefield 1995; Reveal 1985). Penstemon floribundus is unique among the lower elevation taxa for the breadth of its altitudinal distribution (Figure 2); it is reported to occur on a wide variety of substrates derived from volcanic rocks (Danley 1985; Knight 1988). Extensive inventories for P. floribundus, endemic to the remote Jackson Range in northwestern Nevada, have not been conducted and the species may be more common*. Montane Endemics The nine plant species in this group occur within the narrow montane zone dominated by various species of Artemisia or the extensive woodlands of Pinus monophllya and Juniperus osteosperma typical of mountain ranges in the central Great Basin (Figure 2, Table 1). In higher mountains, these forests may be comprised of other conifers, including Abies concolor, P. flexilis, and less commonly, P. longaeva (Charlet 1996). In contrast to the valley endemics, eight of the nine montane taxa occur either on poorly developed soils directly weathered from underlying bedrock, or in scree, talus, or bedrock ledges, cliffs, and crevices (Table 1). The exception is Eriogonum douglasii var. elkoense reported from sandy to gravelly flats and slopes with Artemisia nova and mixed grasses (Reveal 2004b). The primary substrate affinities of the other eight taxa include tuffaceous volcanic sediments (Trifolium andinum var. podocephalum (Barneby 1989) and Eriogonum microthecum var. arceuthinum (Reveal 2004b)), volcanics (Collomia renacta (Joyal 1986), Penstemon pudicus (Reveal and Beatley 1971), and P. tiehmii (Holmgren 1998)), granite (Tonestus graniticus (Tiehm and Shultz 1985)), and carbonates (P. moriahensis (Holmgren 1979), Lewisia maguirei (Holmgren 1954; Williams 1981), and Viola lithion (Holmgren 1992)). In general, these substrates are common regionally and locally and the presumed rarity of these taxa is most likely determined by other ecological or historical factors. High Elevation Endemics Five of the nine high elevation endemics show a preference toward a particular geologic substrate (Table 1). Those reported to occur only on quartzite or other siliceous substrates include Draba serpentina (Al- *Surveys conducted subsequent to the preparation of this manuscript have confirmed P. floribundus to be more common and to occur on the highest peaks of the Jackson Range (A. Tiehm, personal communication).
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December 2012 Number 1 - Utah Native Plant Society

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