Phylogenetics and biogeography of the parasitic genus Thesium L. (Santalaceae), with an emphasis on the Cape of South Africa

Thesium is a large genus of parasitic shrubs belonging to tribe Thesieae of Santalaceae. It has a principally Old World distribution, with the greatest diversity being found in southern Africa. Little is known about the relationships within Thesium or its relationships with its closest relatives. In this article, we present a first estimate of species-level phylogenetic relationships in Thesium based on internal transcribed spacer (ITS) and trnL-trnF sequence data, and use this to explore the biogeographical history of the group. One hundred and four samples representing 72 Thesium spp. were included in a phylogenetic analysis. Plastid and combined data resolve Thesium as paraphyletic relative to Thesidium and Austroamericium with high posterior probability and bootstrap support. ITS sequence data place Thesidium as sister to a large Thesium clade, but with weak support. Ancestral range reconstruction and dating analysis suggest a southern African origin for the group, with a crown age of 39.1 +/- 11.9 Mya, followed by dispersal into Europe and South America. A large clade of Cape species split in the Miocene from a clade comprising tropical species (25.5 +/- 7.3 Mya) with the diversification of extant species beginning at 16.7 +/- 6.3 Mya. (C) 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162, 435-452.