A synoptic revision of Olax L. from Madagascar and the Comoro Island Archipelago is provided based on morphological data gathered from a study of herbarium specimens. We recognize eight species of Olax occurring in this region, including three new species, O. antsiranensis, O. capuronii, and O. mayottensis. Olax antsiranensis has coriaceous leaves with an emarginate apex, a 5-petaled flower, and fruit with a weakly accrescent calyx. Olax capuronii has leaves of similar shape and size, but possesses a 3-petaled flower and a non-accrescent calyx in fruit. Olax mayottensis has larger acuminate leaves, 5 petals per flower, and a fruit which is completely surrounded by an accrescent calyx. All of the newly described species are of conservation concern because of their restricted ranges, with both O. capuronii and O. mayottensis considered endangered. Of the eight species treated here, six species are endemic to Madagascar, O. mayottensis is endemic to Mayotte, and O. dissitiflora occurs in Madagascar, Tanzania, Mozambique, and northern South Africa.
Olacaceae, Olax, Madagascar, Comoros, Mayotte, conservation, new species