Colonization of the Southern Hemisphere by Sagina and Colobanthus (Caryophyllaceae)

Colobanthus (23 species) and Sagina (30–33 species) together are sister to Facchinia. Whereas Facchinia is distributed in western Eurasia, Colobanthus is almost exclusively distributed in the Southern Hemisphere, and Sagina is distributed in both hemispheres with the highest species diversity in western Eurasia. We examined: 1. Whether Sagina and Colobanthus are monophyletic sister genera, 2. Where the two genera originated and how many times dispersal between hemispheres occurred, and 3. Which colonization routes between hemispheres were taken. We reconstructed the phylogeny of Colobanthus and Sagina using nuclear ribosomal internal transcribed spacer (ITS) and two plastid spacers (cpDNA) of altogether 158 ingroup samples of 45 species, and performed molecular dating and ancestral area reconstructions. Sagina and Colobanthus were confrmed as monophyletic sister genera. Biogeographical reconstructions based on ITS and cpDNA showed that Sagina reached the Southern Hemisphere in Australasia or in Africa. For Colobanthus, patterns were less clear and less well-supported: ITS showed Australasia as the region of entry, but cpDNA implied that the Southern Hemisphere may have been entered in America. The extant distributions and the biogeographical histories of Colobanthus and Sagina show both similarities and dissimilarities. This illustrates that biogeographical histories, even of closely related and ecologically very similar lineages, can be highly idiosyncratic.

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