On the systematic position of some Asian enigmatic genera of Asclepiadoideae (Apocynaceae)

Abstract

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 (BSMP = 97, BSML = 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 (BSMP = 37, BSML = 45, PP = 0.79), but all alternative positions are essentially without support. The position of Indian Asclepiadoideae in the family phylogeny is discussed.

Dregea taynguyenensis (Apocynaceae, Asclepiadoideae), a new species from Vietnam

“…Schlechter (1914) treated Dregea as a synonym of Marsdenia Brown (1810: 460), which was followed by Forster (1995). The systematic position of Dregea is indeed close to Marsdenia (Surveswaran et al 2014) but whether the two genera should be considered synonymous could not be ascertained in the phylogeny obtained by Surveswaran et al (2014), due to the insufficient sampling of the two genera and poor resolution of the Marsdenia clade.…”

Cynanchum (Apocynaceae: Asclepiadoideae): A pantropical Asclepiadoid genus revisited

“…ex Benth. was always retrieved outside Cynanchum, and usually in a sister-group position (e.g., , but unresolved with Cynanchinae and Tylophorinae-Asclepiadinae in Surveswaran & al. (2014).…”

“…& Hook.f. (Bruyns & Klak, 2009) and Calciphila Liede & Meve (Liede-Schumann & Meve, 2006) could be established as small but independent lineages, with Schizostephanus considered a member of the Cynanchinae, and Calciphila a member of Asclepiadinae (Endress & al., 2014;Surveswaran & al., 2014). On the other hand, a number of stem-succulent genera, most of them endemic to Madagascar, could be shown to be deeply nested in Cynanchum and were therefore included in the genus: Folotsia Costantin & Bois, Karimbolea Desc., Platykeleba N.E.Br., and Sarcostemma R.Br.…”

“…While Liede & Kunze (2002) retrieved representatives of several other genera (Glossonema Decne., Metalepis, Metaplexis R.Br., Odontanthera Wight, Pentarrhinum E.Mey.) in Cynanchum, they did not consider their evidence sufficient to include those genera in Cynanchum. A recent study, focussing on Indian endemic genera (Surveswaran & al., 2014), also retrieved Graphistemma (Champ. ex Benth.)…”

Jasminanthes xuanlienensis (Apocynaceae, Asclepiadoideae), a new species from Vietnam

“…For instance Gymnema , also considered congeneric with Marsdenia by Forster (1995), was retained in floristic works such as Jagtap and Singh (1999) and Watson (1999). The phylogeny of Surveswaran et al (2014) does not address whether Gymnema should be merged with Marsdenia . The purpose of the present paper is limited to validate a new taxon and we believe that its correct placement is in Jasminanthes .…”