Abstract
The mating system, the physiognomic characteristic and the phenology of two population of a monoecious shrub, Croton suberosus, under shadow and light conditions were compared, and their compatibility and pollination systems studied. There were marked differences in physiognomy, plants under light conditions were higher and more reproductive. There was a trend in both populations to maintain a constant number of female flowers per inflorescence, while the number of male flowers per inflorescence changed and was greater under light conditions. This pattern may be interpreted as a consequence of resource limitation where female allocation is maximized and the remanent resources asigned to male flowers. The numbers of seeds produced under light conditions was significantly higher. Wind was the main pollen vector and plants were found to be self-compatible. Inflorescences are protoginous, although geitonogamia may occur within an individual. There is an alternation of sex ratios within both populations which could indicate that plants respond to an unambiguous environmental cue(s) to begin blooming.
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