The vegetation of characteristic islands in the Indian Ocean is described and related to the stages of denudation of the original limestone rock and to the degree of exposure to prevalent winds and wave action. On the least denuded areas of rocky "pavement," a mixed scrub dominated by Sideroxylon inerme is found, changing to a thicket of Pemphis aridula where the rock has been eroded into "champignon" forms. Mangroves occur in sheltered lagoons on muddy detritus from this erosion. The more exposed shores may develop calcareous sand dunes with dune scrub (mainly Scaevola sp. and Tournejortia argentea) if sufficiently stable. Where spray-moistened sand or shingle occurs, a sward of Sporobolus virginicus is found, and a mat of mixed herbs characterizes areas occupied by guano-forming birds. The guano deposits, now mostly removed, also affect existing vegetation.