December 2012 Number 1 - Utah Native Plant Society

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).