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Faculty for Biology, Chemistry, and Earth Sciences

Department of Plant Systematics: Angiosperm Working Group - Prof. Dr. Sigrid Liede-Schumann

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Surveswaran, S; Sun, M; Grimm, GW; Liede-Schumann, S: On the systematic position of some Asian enigmatic genera of Asclepiadoideae (Apocynaceae), Botanical Journal of the Linnean Society, 174, 601-619 (2014), doi:10.1111/boj.12156&ArticleID=1274866
Key words: classification; chloroplast DNA; India; phylogeny; rbcL; rps16; systematics; trnL; trnL-F

The phylogenetic structure of Asclepiadoideae (Apocynaceae) has been elucidated at the tribal and subtribal levels in the last two decades. However, to date, the systematic positions of seven Asian genera,  Cosmostigma , Graphistemma , Holostemma , Pentasachme , Raphistemma , Seshagiria and Treutlera , have not been investigated. In this study, we examine the evolutionary relationships among these seven small enigmatic Asian genera and clarify their positions in Asclepiadoideae, using a combination of plastid sequences of rbcL , rps16 , trnL and trnL- F regions. Cosmostigma and Treutlera are resolved as members of the non-Hoya clade of Marsdenieae with strong support (maximum parsimony bootstrap support value BSMP = 96, maximum likelihood bootstrap support value BSML = 98, Bayesian-inferred posterior probability PP = 1.0). Pentasachme is resolved as sister of Stapeliinae to Ceropegieae with moderate support (BSMP = 64, BSML = 66, PP = 0.94). Graphistemma , Holostemma , Raphistemma and Seshagiria are all nested in the Asclepiadeae–Cynanchinae clade (BS MP = 97, BS ML = 100, PP = 1.0). The study confirms the generally accepted tribal and subtribal structure of the subfamily. One exception is Eustegia minuta , which is placed here as sister to all Asclepiadeae (BSMP = 58, BSML = 76, PP = 0.99) and not as sister to the Marsdenieae + Ceropegieae clade. The weak support and conflicting position indicate the need for a placement of Eustegia as an independent tribe. In Asclepiadeae, a sister group position of Cynanchinae to the Asclepiadinae + Tylophorinae clade is favoured (BSMP = 84, BSML = 88, PP = 1.0), whereas Schizostephanus is retrieved as unresolved. Oxystelma appears as an early-branching member of Asclepiadinae with weak support (BSMP = 52, BSML = 74, PP = 0.69). Calciphila and Solenostemma are also associated with Asclepiadinae with weak support (BS MP = 37, BS ML = 45, PP = 0.79), but all alternative positions are essentially without support. The position of Indian Asclepiadoideae in the family phylogeny is discussed. 

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