A molecular–morphological approach solves taxonomic controversy in arctic Draba (Brassicaceae)

Abstract

We used a combined molecular and morphological approach to solve a long-term controversy in the taxonomically complex genus Draba L. (Brassicaceae): the delimitation of Draba lactea Adams versus Draba fladnizensis Wulfen. We also tested hypotheses on the origin of D. lactea, which has been reported as hexaploid and possibly derived from the diploids D. fladnizensis, Draba nivalis Liljeblad, and (or) Draba subcapitata Simmons. In an initial analysis of large population samples of three of these autogamous species, intrapopulational isozyme variation was low or absent (mean genotypic diversity, D, was 0.10), the diploids were almost invariably homozygous, and D. lactea was highly fixed-heterozygous. In the main analysis, we examined 35–47 populations of the four tentative species from the arctic archipelago of Svalbard for variation in isozymes, random amplified polymorphic DNAs (RAPDs), and 36 morphological characters. Multivariate analyses of the RAPD data revealed four very distinct groups of multilocus phenotypes. These groups also differed in several morphological characters and corresponded to the four tentative species. The species were less differentiated at isozyme loci, in particular the diploids D. fladnizensis and D. subcapitata, but D. lactea was clearly distinguished from D. fladnizensis based on all three data sets. Contrary to most earlier suggestions, the hexaploid D. lactea was genetically more similar to D. subcapitata than to D. nivalis, but our analyses of the material from Svalbard did not give conclusive evidence on the origin of this widespread arctic hexaploid.Key words: arctic, Draba, isozymes, morphology, polyploidy, RAPDs.