What data determine whether a plant taxon is distinct enough to merit legal protection? A case study of Sedum integrifolium (Crassulaceae)

Measures of molecular and morphological genetic variation are often used to set conservation priorities and design management strategies for plant taxa. Evaluated together they can give insights into a taxonʹs evolutionary status that neither data type alone can achieve. We investigated the distinctness and variability of Sedum integrifolium ssp. leedyi, a federally and state-listed taxon, from its conspecific relatives using 33 random amplified polymorphic DNA (RAPD) markers (253 plants) and 37 morphological characters from 1308 common-garden-grown plants. We included S. integrifolium ssp. leedyi (four populations), its conspecific relatives (11 populations), and S. rosea and S. rhodanthum populations in our study. The morphological and molecular data correspond in showing that S. integrifolium ssp. leedyi populations are highly distinct. However, the data sets differ in their estimates of the relatedness of some S. integrifolium ssp. leedyi populations and in the percentage variation detected due to differences among them (25 and 9–13% for the molecular and morphological data, respectively) suggesting little gene flow among populations and some differentiation, possibly from selective pressures. Given our data, we recommend that S. integrifolium ssp. leedyi merits protection under the U.S. Endangered Species Act and that its populations be managed as distinct units.