A general overview is presented of the Ankarana massif, a karstic formation in northern Madagascar, summarizing information on climate, geology, and geomorphology, followed by observations from the central portion of Ankarana near the Lac Vert concerning dry deciduous forest, which represent the climax formation in Madagascars Western phytogeographic domain. The phenology of the local flora is characterized by the almost complete seasonal loss of leaves during the dry season, and by a peak in flowering prior to the onset of the rains. Three formation can be recognized at Ankarana based on floristic composition and physiognomy of the vegetation; the occurrence of each is correlated with variations in edaphic conditions, which are the most important ecological factors influencing the vegetation in this area. Several examples of species with special adaptations are described, including geophytes with a short vegetative cycle, and plants exhibiting crassulence, pachycauly, and spinescence; these are discussed with regard to the sites at which they grow. Three new species from this region are described in Chlorophytum (Liliaceae), Tacca (Taccaceae) and Adenia (Passifloraceae).