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Plants of the corymbosum complex are common in sandy substrates on the Colorado Plateau from southwestern Wyoming through western Colorado, eastern Utah, northern New Mexico, and Arizona. Within this complex a key feature for considering the Las Vegas buckwheat a distinct variety is its marked preference for gypsum soils (Reveal 2002, p. 26). Susan Meyer (1986, p. 1308) described the Las Vegas buckwheat as a gypsocline, a species that principally occurs on gypsum but is also found on other unusual substrates such as claybeds and high-boron shales. Using soil test pits, Drohan and Buck (2006, p. 12) determined the Las Vegas buckwheat typically occurs on deeper soils than the Las Vegas bearpoppy (Arctomecon californica) another endemic gypsocline that shares much of the same habitat preferences and range. Typically, gypsum soil outcroppings occupied by Las Vegas buckwheat are sparsely vegetated with bare exposed soils covered with a cryptogammic soil crust. Although a specific vegetation classification for Las Vegas buckwheat habitat does not exist, it generally can be differentiated from typical Mojave creosote-bursage scrub and saltbush scrub that usually surrounds it by the presence of gypsophiles (gypsum obligate species) and other gypsoclines that occasionally share habitat, including the Las Vegas bearpoppy, Parry sandpaper plant (Petalonyx parryi), Palmer's phacelia (Phacelia palmeri), wingseed blazing star (Mentzelia pterosperma) and froststem suncup (Camissonia multijuga) (Meyer 1986, p. 1308).
Because the taxonomy of the Las Vegas buckwheat was only recently resolved in 2006, there is very little information regarding the historic range and distribution of the variety. Based on herbarium records, Las Vegas buckwheat is historically known from three locations in Clark County: Las Vegas Valley, Gold Butte, and Muddy Mountains (Service 2000, p. 9). The distribution of all known (current and historic) occurrences in southern Nevada is shown in Figure 1. Based on all records for the variety (herbarium records, surveys of undeveloped parcels in the Las Vegas Valley), the Las Vegas Valley historically contained the primary distribution of the variety. Based on U.S. Geological Survey soils mapping, there are approximately 88,000 acres of suitable soils for the variety in the Las Vegas Valley (Figure 2). However, this is likely an overestimate of the historic occurrence of the variety within the Las Vegas Valley because additional biotic and abiotic factors that regulate recruitment and reproduction (including pollination biology, seed dispersal, soil depth and local hydrology) would also limit its distribution within suitable soils. There is no information available to infer the number of plants historically present |
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the present or threatened destruction, modification, or curtailment of its habitat or range; inadequacy of existing regulatory mechanisms; stochastic effects, nonnative species, climate change |
