PHYLOGENY OF APOCYNOIDEAE AND THE APSA CLADE (APOCYNACEAE S.L.)1

Abstract

Phylogenetic relationships were reconstructed among 59 of 77 genera of subfamily Apocynoideae and exemplars of Periplocoideae, Secamonoideae, and Asclepiadoideae (collectively the APSA clade) using sequences from four regions of the chloroplast genome (trnL intron and trnL-trnF spacer, rpl16 intron, rps16 intron, matK and 3′ half of trnK intron) and 16 morphological characters. Apocynoideae are resolved as paraphyletic. The five tribes recognized within this subfamily in the classification of Endress and Bruyns are all paraphyletic or polyphyletic. Seven major clades of Apocynoideae are identified. The first three include genera classified predominantly in tribes Wrightieae and Malouetieae sensu Endress and Bruyns and form a paraphyletic grade to a crown clade. The crown clade includes four clades of Apocynoideae genera classified in tribes Apocyneae, Mesechiteae, and Echiteae together with Periplocoideae, Secamonoideae, and Asclepiadoideae; the latter three constitute the traditional Asclepiadaceae. Asclepiadaceae are resolved as polyphyletic, although the node that precludes a paraphyletic Asclepiadaceae does not have bootstrap support. The clade of Secamonoideae–Asclepiadoideae is well supported as sister to a clade of three African Apocynoideae genera (Baissea A. DC., Motandra A. DC., and Oncinotis Benth.). There is a strong correlation between geographic distribution and phylogeny among crown clade Apocynoideae. A New World clade is composed of American genera plus the predominantly Australasian Parsonsia R. Br. and Artia Guillaumin. An Asian clade is composed of Asian, Malesian, and Australasian genera plus the north temperate Apocynum L. Trachelospermum Lem. is polyphyletic with American and Asian species nested in the New World and Asian clades, respectively. The implications of this phylogeny for the evolution of pollen aggregation and mass transfer, the traits that were used to separate Asclepiadaceae from Apocynaceae s. str., are discussed.