December 2012 Number 1 - Utah Native Plant Society

Utah Native Plant Society
“escape route” (Grabherr et al. 1995; Halloy and Mark
2003). Perhaps this can be attributed to unusual features
of plant endemism in the western United States in general
and, more specifically, in the Intermountain West.
Kruckeberg (1986) reformulated earlier works characterizing
the processes of soil formation and vegetation
development (Jenny 1941; Major 1951) to account for
plant diversity in any region. He noted that topography,
parent material, and the timing of geological processes
or events created a patchiness or discontinuity of edaphic
phenomena that creates additional opportunity for
biological discontinuity. i.e., speciation. He termed endemic
taxa that result from this process “geoedaphics”
(Kruckeberg 1986). Rajakaruna (2004) provided a
review that emphasized the role that unusual soil conditions
play in the diversification of plant species.
Although Kruckeberg (1986) emphasized the role of
bedrock (and especially serpentine) outcrops in the evolution
of geoedaphics, in an earlier paper Kruckeberg
and Rabinowitz (1985), cast a broader net with respect
to narrowly distributed endemics (sensu Mason
1946a,b), noting that unique taxa associated with
“gypsum, serpentine, limestone, alkaline and heavy
metal soils are well known to field botanists in many
parts of the world.” While few, if any, serpentine outcrops
are known from the Great Basin in Nevada, the
Calcareous Mountains Section of the Intermountain region,
which lies primarily in the eastern half of Nevada
and adjacent southwestern Utah, is recognized as the
richest area of the Great Basin for plant endemism
(Holmgren1972a). Elsewhere, examples of Great Basin
plants restricted to exposures of carbonate bedrock are
Figure 2. Elevation ranges of reported localities of the 33 rarest plants (NatureServe G1, G1G2, and T1 ranks) in the
Great Basin of Nevada. The rectangles in each box-and-whisker plot show the 50 percent of the populations that occur
between the 25 th and 75 th percentiles and the median elevation. Species are ranked by median elevation. Circles
indicate plants known from only a single site. Shading shows plants endemic to Nevada.
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