The campos de murundus (carthmound fields) are typical landscapes of the cerrado (savanna) region of Central Brazil and are characterized by many rounded earthmounds called murundus which are scattered over a grassland surface. As these areas are normally liable to seasonal water-logging, the earthmounds are true habitat islands capable of bearing woody plants typical of the cerrado, which are normally very intolerant of root inundation. The vegetation of an area of murundus field at Cuiaba, in the State of Mato Grosso, Central Brazil, was surveyed for the purpose of evaluating the island-effect on the plant community growing on the mounds/islands. Two main aspects were considered:the influence of the size of the mound and the differences between the types of cerrado occurring on the mounds and on the areas surrounding the murundus field. Most plant species occurring on the mounds were also present in the flora of the surrounding cerrado. However, only a fraction of these species was able to colonize the mounds successfully. The number of species on the mounds was found to be significantly correlated with mound area. Species-area relationships were better described with the power model S — C(A/) than with the exponential model S — C T z (logA) (fitted with linear regression). The mound size also had a strong influence on the spatial distribution of the species on the surface of the mounds. The species were organized in an increasing number of concentric topographic belts corresponding to a gradient of soil depth above the flooding level. © 1992, Cambridge University Press. All rights reserved.