Molecular evidence for allopolyploid speciation and a single origin of thenarrow endemic Draba ladina (Brassicaceae)

Draba ladina (Brassicaceae) is a small alpine flower endemic to the Swiss A lps. It occurs exclusively at elevations between 2600 and 3000 m and is res tricted to less than a dozen mountains in the Lower Engadin. Morphological characters and polyploidy suggest a hybrid origin. Potential diploid progen itor species are distributed widely and often occur sympatrically. To study the evolutionary history of D. ladina we assessed intra- and interspecific sequence variation at noncoding chloroplast DNA loci and nuclear rDNA ITS sequences in D. ladina and its presumed progenitor species D. aizoides, D. dubia, and D. tomentosa. A single ITS (Internal Transcribed Spacer) genotyp e was found in each of D. aizoides and D. dubia and two in D. tomentosa. Ad ditivity of ITS sequences of D. aizoides and D. tomentosa was found in D. l adina, supporting the hypothesis of an allotetraploid origin. Intraspecific cpDNA variation was found in all diploid species, but not in D. ladina. Th e single chloroplast DNA haplotype found in the latter was closest to one c pDNA haplotype found in D. tomentosa, suggesting that D. tomentosa was the maternal parent. These results suggest that D. ladina is a relatively young , presumably postglacial, taxon with a single allopolyploid origin.