关键词: Melastoma malabathricum, 花部形态, 花粉, 传粉, 繁育系统

Abstract

Heteranthery in flowers has often been explained by Darwin’s ‘division-of-labor’ hypothesis. In order to test the hypothesis, we examined pollination pattern and the roles of two dimorphism stamens in pollination in Melastoma malabathricum; this species contains two sets of stamens differing markedly in shape, size and color. We found differences in morphological characters, numbers of pollen grains, seed sets following experimental treatments, with stamens removed and pollinator behaviour between the two types of stamen. The anther of purple stamens contained more pollen grains than that of yellow stamens. Carpenter bees (genus species) alighted only on the yellow stamens, and grasped their five anthers. Flowers that had their yellow stamens removed set significantly fewer seeds than intact flowers. There was no difference in the seed set of flowers with purple stamens removed and intact flowers. These results suggest that the yellow anthers function to attract pollinators and satisfy the insects’ demand for pollen, and the purple anthers satisfy plant’s need for safe gamete dispersal. However, there were no differences in pollen viability, histochemistry, or fruit set between anther type, suggesting the lack of physiological differentiation. Our experimental manipulations also demonstrate the absence of self-pollination and agamospermy in Melastoma malabathricum, and that the breeding system is facultative xenogamy.

Key words: Melastoma malabathricum, floral morphology, pollen, pollination, breeding system