Further fragmentation of Timonius (Rubiaceae): reinstatement of Abbottia based on morphology and molecular sequence data

Abstract

The circumscription of the Paleotropical dioecious and species‐rich genus Timonius Rumph. ex DC. nom. cons.has long been based on a restricted combination of morphological features, namely valvate corolla aestivation and drupes bearing multiple, free, single‐seeded pyrenes. Previous studies, focused on different taxonomic problems in tribe Guettardeae, found Timonius to be either monophyletic or polyphyletic, but these studies relied only on a limited number of species. Based on these, the phylogeny of Timonius and related genera is here reconstructed using sequences obtained from five nuclear and plastid molecular loci (ETS, ITS, atpB‐rbcL, rps16 and trnT‐F) to provide a better understanding on its generic boundaries. The phylogenetic results generally affirm the unnaturalness of Timonius, and its species fall into three well‐supported clades: 1) Abbottia clade, containing representatives of T. subgen. Abbottia, 2) Timonius clade, containing the majority of the sampled species of Timonius, and 3) the New Caledonian endemic Timonius platycarpus is recovered in an isolated position that is sister to Tinadendron. These findings are supported by morphological characters and molecular apomorphies, implying the need to resurrect the genus Abbottia with an amended diagnosis. Diagnostic morphological characters of the Timonius clade are also presented toward a more stable taxonomy of the genus.