Taxonomic Delimitations within the Penstemon scariosus Pennell (Plantaginaceae) Complex

We examine the 4 recognized varieties of Penstemon scariosus that constitute a complex of related taxa that share overlapping morphological characters: namely varieties albifluvis, cyanomontanus, garrettii, and scariosus. Modern taxonomic descriptions and associated keys are not in complete agreement on how to clearly delineate these varieties. It is particularly important to understand the taxonomic circumscription of variety albifluvis, since it is being considered for listing under the Endangered Species Act. To address the taxonomic position of taxa in this species complex, we examine the genetic structure of 66 accessions of P. scariosus, representing the 4 known varieties, across its entire known geographic range using 10 SSR (microsatellite) markers. We also examine plant morphology of these taxa from 264 herbarium specimens. The results of our molecular and morphological studies give rise to 4 conclusions. First, due to the genetic distinctiveness of P. scariosus var. albifluvis and its geographical isolation, we consider conserving its original status at the species level. Second, our molecular study suggests that the geographic area for var. cyanomontanus is much larger than previously understood, consisting of plants and populations with or without the characteristic glandular hairs that have been used to identify that taxon. Third, both our molecular and morphometric data suggest that varieties garrettii and scariosus are not reliably separable and should be considered the same taxon. Finally, our molecular data reveal a distinct genotype from the Tabby Mountain, Utah, area that has not previously been given taxonomic recognition. We describe this new taxon and provide a taxonomic key to separate this new variety from the other members of the species complex. Examinamos las cuatro variedades reconocidas de Penstemon scariosus que comprenden un complejo de taxones relacionados que comparten caracteres morfológicos superpuestos: las variedades albifluvis, cyanomontanus, garrettii y scariosus. Las descripciones taxonómicas modernas y las claves asociadas no están completamente de acuerdo en cómo delimitar claramente estas variedades. Resulta especialmente importante entender la circunscripción taxonómica de la variedad albifluvis, debido a que se ha considerado su inclusión en la Ley de Especies Amenazadas. Para abordar la posición taxonómica de los taxones en este complejo de especies, examinamos la estructura genética de 66 registros de P. scari