Temporal and spatial diversification of the African disjunct genus Androcymbium (Colchicaceae)

The genus Androcymbium (Colchicaceae) includes 57 species that are distributed in the extreme northern and southern portions of Africa, mainly in regions with a Mediterranean climate. We present the first phylogeographic analysis of the genus with species from all five of its distribution areas (North Africa, Horn of Africa, Namibia, western South Africa, and eastern South Africa). We used sequence data from six chloroplast regions and one nuclear region. Phylogeographic reconstructions were conducted using both parsimony and Bayesian inference methods. Molecular dating estimates using a Bayesian approach suggest a middle Miocene (13.4 ± 1.5 mya) origin of the genus; this approach also provides support for a late Miocene (9.6 ± 1.7 mya) diversification in the winter-rainfall area of western South Africa–south of Namibia and strongly influenced by the Benguela current. Three northward dispersion events have been reported in Androcymbium. The first dated to the end of the Miocene (7.0 ± 2.0 mya) and gave rise to the genus Colchicum. The second and the third dispersion events took place in the mid Pliocene, rising one from eastern South Africa and originating the only species found in the Horn of Africa (3.0 mya), and the other from Namibia to the Mediterranean basin (4.0 mya). The formation of a late Miocene–Pliocene arid track in the east of Africa is of a great importance to explain these northward dispersions in Androcymbium.