Systematics, phylogeography and multiple origins of morphs in two species complexes belonging to Cistaceae, Helianthemum oelandicum and H. nummularium

Abstract: The Helianthemum oelandicum complex shows considerable morphological variation across its geographic distribution in Europe and western Asia. By combining four primer pairs and four restriction enzymes I identified nine cpDNA haplotypes with distinct geographical distributions. Two haplotypes were most frequent over most of the range; one in western Europe and one in eastern Europe. Moreover, differences in haplotype composition were much more strongly pronounced in west-east direction than in south-north direction. There was no correlation between chloroplast haplotype and morphological variation. Parallel evolution in the regional populations produced similar morphologies without necessarily being closely related. The complex on Öland is represented by two endemic and allopatric varieties, differing in flowering phenology and indumentum. Variety oelandicum has a wide distribution, while var. canescens is restricted to small areas in the southernmost Öland. Only two, allopatrically distributed, cpDNA haplotypes are detected in the present study. The border between the distributional areas of the two haplotypes is distinct and cuts across extensive, more or less continuous populations of var. oelandicum. This border coincides with marked differences in the frequency of hairy and glabrous plants. The phylogenetic analysis of the ITS and cpDNA revealed poorly resolved trees in the Helianthemum oelandicum complex; taxa were polyphyletic. The H. nummularium complex is a morphologically variable species that has been subdivided into several subspecies, primarily based on indumentum characters. I investigated five of these subspecies for variation in chloroplast DNA and leaf and petal shape in Europe. The highest haplotype diversity was found in the Alps and the surrounding lowland areas, whereas marginal areas such as northern Europe and southeastern Balkans had low diversity. Most of the common haplotypes were shared between subspecies and showed distinct geographic structures across the species range. Leaf and petal shape descriptors could not differentiate between subspecies. It is concluded that the poor correspondence between chloroplast haplotype distribution and subspecies circumscription is due to multiple origins of morphologically similar morphs in different parts of the distribution range of the complex.