A DIRECTIONAL CLINE IN MOURIRI GUIANENSIS (MELASTOMATACEAE)

Abstract Morphological variation in Mouriri guianensis is described and analyzed throughout its range in Brazil and adjacent regions. Features that vary are ovary size, locule and ovule number, shape and smoothness of the leaf blade and petiole length. The largest ovaries with the most ovules occur in west central Amazonia; intermediate sizes and numbers are widespread but reach the coast only between Marajó and Ceará; and the smallest ovaries with the fewest locules and ovules are coastal or nearcoastal from Delta Amacuro in Venezuela to Marajó. Small ovaries also occur in coastal Alagoas and at Rio de Janeiro. Ovaries with the fewest locules and ovules are believed to be the most specialized, the result of evolution toward decreased waste of ovules, since the fruits of all members are few-seeded. Leaf characters correlate statistically with ovule numbers. Possible origen of the distribution pattern of the species is compared in terms of present rainfall patterns and in terms of Pleistocene climatic change with associated forest refuges. It is concluded that both phenomena were probably influential. High specialization appears to have accompanied isolation, for reasons that are unclear. Because the plants from Delta Amacuro to Marajó are the most specialized they may once have been more isolated than now.