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. Featu res 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 locu les 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 appe ars 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.

New Species and Other Taxonomic Matters in the New World Memecyleae (Melastomataceae)

“…A similar trend was found in M. guianensis, where the conclusion was that the greater number was primitive (Morley, 1983). In M. gleasoniana the presence of the larger numbers close to South America, where the genus appears to have originated, with the smaller numbers to the north, where the environment gradually becomes more extreme, suggests that the same interpretation should be made in this species.…”

“…This species is best placed in the sect. Mouriri (Morley, 1976: 36) on the basis of its tubular midrib xylem, small Type II stomatal crypts, hypodermis, acuminate leaf apex, axile-basal placentation, and relatively short thecae. Section Litophyllum is very similar, differing only in its lack of a hypoderms.…”