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Plant species richness in the Cape Verde archipelago is examined relative to island eco-geographical factors. Species-area and species-area-habitat relationships are analysed using the classical species-area model and the recently proposed species-choros model. The number of floristic zones (used to estimate the choros parameter) provides an adequate estimate of the potential habitat diversity, and the species-choros model achieved a better fit with both total flora and endemic species. In addition to area and habitat diversity, longitude also emerges as an important determinant of species diversity, whereas latitude, minimum distance to the nearest island, and total rural population do not display any correlation. As in other insular ecosystems, the species richness (about 140 per 100 km(2)) is lower than in nearby mainland regions; the proximity to the desert areas of the Sahel can also be seen as related with this low value. The floristic heterogeneity in Cape Verde is high, as is usual in island ecosystems. In a comparative analysis of the species richness on the different islands (using alpha-values), Brava stands out as having the highest total flora species densities, while for endemic flora Brava and Sao Nicolau jointly occupy the leading position. The high diversity for both total and endemic species on Santo Ant (a) over tildeo, S (a) over tildeo Vicente, S (a) over tildeo Nicolau, Fogo and Brava reinforces their importance in conservation terms - in the case of most of them, something that is already recognized in the established network of protected areas.