Endemic families of Madagascar. VIII. A synoptic revision of Xyloolaena Baill. (Sarcolaenaceae)

As part of an assessment of the vascular plant families endemic to Madagascar and the Comoro Islands, a synoptic revision is presented of Xyloolaena Baill. (Sarcolaenaceae). Molecular sequence data place the family sister to Dipterocarpaceae in a broadly defined Malvales. Fossil pollen tetrads of Sarcolaenaceae from the Miocene of South Africa most closely resemble those of Xyloolaena, indicating that Sarcolaenaceae were once more widely distributed. Xyloolaena appears most closely related to Rhodolaena, Sarcolaena and Leptolaena sensu lato, with which it shares several features; Xyloolaena can be distinguished by its involucre that forms a cup at anthesis instead of completely enclosing the flowers, and its numerous multiseriate ovules. Five species are recognized, two of which are newly described (X. sambiranensis and X. speciosa). Xyloolaena linearifolia Cavaco is excluded from the genus. Preliminary assessments of the conservation status of each species are provided, along with a key to the species in English and French.