Molecular phylogenetics of Sarcolaenaceae (Malvales), Madagascar's largest endemic plant family

With 72 species belonging to ten genera, Sarcolaenaceae are the largest and most diverse of Madagascar's endemic plant families. Comprising shrubs and trees, with members found in nearly all of this island nation's biogeographic regions, they are characterised by the presence of a distinctive extra-floral involucre that is more or less accrescent, partially or completely covering or enveloping the fruit. We present the first molecular phylogenetic study of Sarcolaenaceae, using broad sampling that encompasses the family's taxonomic and morphological diversity, including 46 species representing all ten genera and sequence data from one nuclear marker (ITS) and three plastid regions (psaA-ORF170, psbA-trnH and rbcL), to reconstruct phylogenetic relationships using Bayesian inference and maximum likelihood. Results confirm the monophyly of Sarcolaenaceae and of eight of the ten genera; the monophyly of Rhodolaena remains ambiguous, although the taxa sampled were recovered in two well supported clades that are coherent in terms of morphology and geography. Only a single species of Eremolaena was available for study. The phylogenetic backbone of Sarcolaenaceae is not fully resolved, making it difficult to identify potential morphological synapomorphies or ecological preferences between and within genera. In the family, two monophyletic groups were, however, found [Pentachlaena + Eremolaena + Perrierodendron (Clade A) and Xyloolaena + Leptolaena + Sarcolaena + Mediusella + Xerochlamys (Clade B)] that are consistent with previous results based on morphology. Expanded species sampling and data from additional, more quickly evolving markers will be needed to produce a fully resolved phylogenetic tree for Sarcolaenaceae, which could then serve as a basis for exploring macroevolutionary patterns and processes in this remarkable family and reconstructing its biogeographic history.