Dioecy in the Cerrado vegetation of Central Brazil

Abstract

Summary Occurrence of dioecy in Cerrado, Neotropical savanna region in Central Brazil, is analyzed here. Frequency of dioecious species and their phenological and morphological characteristics were studied for a cerrado woody community near Brasilia, and a broader comparative survey was done using phytosociological data for different cerrado areas and vegetation physiognomies. Nine dioecious species were found in the studied community (15% of the species in the area), most with simple open flowers visited by small insects. Flowering phenology differed from species to species including long, sparse flowering and comucopian strategies. Distance between flowering individuals varied from 13 to 70 m. Gender related differences in spatial distribution and in height or circumference were tested for three of the species and significant departure from random was found only for Rapanea guianensis . The regional survey showed frequencies of dioecy higher in denser woodlands and forest than in open cerrado areas. Most species presented small promiscuous flowers, probably associated to pollination by small insects, and fleshy fruits. Among the species occurring in the cerrado areas one could separate a group of dioecious shrubs and treelets really adapted to cerrado environment and another group of evergreen forest species which occur only in denser woodlands, the cerradao. Differences in the frequency of dioecy seems to be related to the occurrence of this latter group and the appearance of cerradao.