DNA markers and morphometry reveal multiclonal and poorly defined taxa in an apomictic Cotoneaster species complex

Taxonomy in the apomictic genus Cotoneaster L. has been controversial. Two Scandinavian species were recently described from C. integerrimus s.l., C. canescens Vestergr. ex B. Hylmo and C. scandinavicus B. Hylmo. Morphometric analyses of leaf shape and DNA marker analysis with RAPD were applied to investigate the differentiation between these two tetraploid species, and determine whether two morphologically aberrant variants of C. scandinavicus, informally known as "balticus" and "gotlandicus", deserve taxonomic recognition. These taxa proved rather difficult to distinguish with morphological characters and RAPD data suggested an even more continuous pattern of variation. The geographically and morphologically narrowly delimited, prostrate C. scandinavicus "gotlandicus" was relatively homogenous but very close to other glabrous-leaved, more erect genotypes. The more broadly delimited C. canescens, C. scandinavicus and C. scandinavicus "balticus", however, completely overlapped genetically. These results are in contrast to the relatively high concordance between morphology-based and molecular marker-based discontinuities that has been reported in some other apomictic genera. Most likely, differences among apomicts in endosperm formation, propensity for fertilization and colonization history, are the culprits behind this lack of a consistency.