A NEW SPECIES OF DESERT-ASTER (XYLORHIZA, COMPOSITAE–ASTEREAE) FROM THE COTTONWOOD MOUNTAINS AND ADJACENT PANAMINT RANGE OF CALIFORNIA'S DEATH VALLEY REGION

Xylorhiza panamintensis B.G.Baldwin & M.Berger is described as a new species from carbonate bedrock exposures in the southern Cottonwood Mountains and adjacent Panamint Range west of Death Valley in the Mojave Desert of southeastern California. Unlike other species of Xylorhiza, X. panamintensis is a compact, densely leafy, glandular-hirsute to glandular-hirtellous shrub with leaves spinose-margined, ±ovate to mostly narrowly elliptic or oblanceolate, heads often in densely corymbiform capitulescences with involucres broadly obconic to campanulate, ≤2 cm diam, ray florets 19–29, ray corolla laminae 6–11.5 × 1–1.75 mm, 6.5–9.5 mm long, disk corollas narrowly cylindric to slightly funnelform, style branch appendages ca. as long as stigmatic lines, cypselae sericeous, and pappus bristles 15–25, the longest 5.5–10 mm long, white to tawny. Morphologically, X. panamintensis is not easily confused with other taxa of Xylorhiza. Comparison of nuclear ribosomal internal transcribed spacer (ITS) DNA sequences across the genus revealed diagnostic nucleotide states shared by all three representatives of the new species. Samples of the new species were resolved in ITS phylogenetic analyses as constituting a well-supported lineage most closely related to X. tortifolia sensu lato. Discovery of X. panamintensis reinforces evidence for floristic endemism in the Death Valley region and for evolutionary divergence of desert lineages in Xylorhiza. Although all known populations receive protection by occurring within Death Valley National Park, the small number of individuals found to date indicates that X. panamintensis warrants conservation concern as potentially vulnerable to climate change, to any local anthropogenic impacts to its limited habitat, or to stochastic events.