How to kill two genera with one tree: clarifying generic circumscriptions in an endemic Malagasy clade of Sapindaceae

Phylogenetic relationships in a Malagasy clade of Sapindaceae, encompassing Molinaea (with members also in the Mascarene Islands), Neotina, Tina and Tinopsis, were inferred by expanding a previous nuclear and plastid DNA data set for the family. The circumscription of these morphologically similar genera has remained problematic since the first family-wide treatment. To investigate this situation, representative taxa were analysed to: (1) test the monophyly of the genera; (2) investigate their phylogenetic relationships; and (3) explore alternative circumscriptions that reflect phylogeny and yield genera that are morphologically coherent and easily characterized. Phylogenetic inferences supported the monophyly of the group and its subdivision into three clades. All species of Molinaea sampled belong to a clade (Clade I) that is sister to a clade comprising Neotina, Tina and Tinopsis, within which one clade (Clade II) encompasses Tinopsis and Neotina (with the latter nested within the former) and another (Clade III) comprises all taxa of Tina. These three genera can be easily distinguished from Molinaea by having two rather than three carpels, which represents an unambiguous synapomorphy. Given the paraphyly of Tinopsis with regard to Neotina and the strong support for the monophyly of Tina, two potentially viable options are available for the generic delimitation of the taxa in this clade: (1) to recognize two genera corresponding, respectively, to Clades II and III; or (2) to place all of the taxa in a single genus encompassing both clades. Based on a review of morphological evidence the second option is favoured and consequently a broad generic concept is applied. (c) 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 165, 223-234.