VincetoxicumandTylophora(Apocynaceae: Asclepiadoideae: Asclepiadeae)—two sides of the same medal: Independent shifts from tropical to temperate habitats

Abstract

AbstractA revised phylogeny of Tylophorinae, based on 77 species of all genera presently attributed to the subtribe(Biondia, Blyttia, Diplosstigma, Goydera, Pentatropiss, Pleurostelma, Rhyncharrhena, Tylophora, Vincetoxicum)is presented. Five chloroplast markers(trnT–L,trnL–F,andpssbA–trnHintergenic spacers as well as thetrnLandtrnGintrons) and two nuclear markers (ITS, ETS) were used, totalling in 3809 base pairs. Tylophorinae are strongly monophyletic and consist of several well–defined clades. Backbone resolution between these clades is low, indicating a rapid early radiation.Pentatropissis sister to all remaining taxa, albeit with weak support; all other taxa form one big clade not corresponding to previous generic delimitations. Therefore, all genera except forPentatropissare subsumed underVincetoxicum.The early branching clades ofVincetoxicums.l. all grow in Africa, where the group originated ca. 18 Ma ago, correlating with the closure of the Tethys Ocean. The first round of differentiation took place between 12 and 15 Ma ago, resulting in Tylophorinae being distributed over almost all of their present range except for South Africa, Arabia and Europe. Two unrelated lineages of temperate, mostly erect plants hitherto named‘“Vincetoxicum”have arisen from more tropical lineages, hitherto named“Tylophora”.One clade of African species is nested inside the Australasian assemblage; this clade contains exclusively polyploid species and its re–immigration to Africa took place in the Messinian, at ca. 6.8 Ma. The EuropeanVincetoxicumspecies split from erect steppe plants of temperate Asia at ca. 4.5 Ma, coinciding with the uplift of the Tibetan plateau. This group contains two species that are presently aggressively spreading in North America after chance introductions.