Taxonomic revision and numerical analyses of Leptolaena sensu lato subgenera Mediusella and Xerochlamys (Sarcolaenaceae)

Among the genera of Sarcolaenaceae, the largest endemic plant family of Madagascar, the taxonomy of Leptolaena Thouars sensu lato is certainly the most controversial. Previous studies attempted to define species circumscription as well as to clarify the systematic position of the subgenera Xerochlamys (Baker) Cavaco and Mediusella Cavaco. The current taxonomy of these two subgenera appears to underestimate morphological patterns of variation. The goal of the present study is to delimit species within subgenera Mediusella and Xerochlamys using multivariate statistical analyses of morphological data taken from herbarium specimens. Principal Component Analysis (PCA) based on correlation matrices was used to analyze morphological variation among groups of specimens. Discriminant analysis was carried out to clarify boundaries between the hypothetical species. Results showed that ten groups can be distinguished based on vegetative, floral and fruit characters, with fairly good support. Groups obtained from the numerical analyses were used to propose a new taxonomic framework for Leptolaena sensu lato. Three new species ( L. coriacea, L. itremoensis and L. undulata) are described, two others (L. elliptica and L. tampoketsensis ) are elevated to species rank and the last five constitute the species recognized in the most recent treatment of Leptolaena. The conservation status of the species recognized was evaluated according to IUCN criteria, three species are considered endangered, two are vulnerable, two others are classified least concern and the last three are nearly threatened.