Merostachys riedeliana Rupr. is a long-lived monocarp species common in the understorey of tropical semideciduous forest fragments in the south of Minas Gerais, Brazil. Its floral biology and breeding system were studied and compared with others bamboos. Due to its rhizome, it occurs in clumps and has a remarkable capacity for vegetative multiplication, which ceases a few months before the emergence of the first inflorescences. The beginning of the flowering and the death of the entire population occurred respectively on October 1998 and May 1999. The peak of the blooming episode took place during the hot and rainy months of the year (December and January). Each inflorescence produces in average 29 spikelets, which have hermaphrodite florets with three stamens and two plumose stigmas that are exposed during theanthesis. The abundant pollen is easily released by the wind or visitors. Apis mellifera L. and Trigona spinipes (F.) were the commonest visitors and behave as pollen thieves. These bees occasionally act as devices for dispersion of pollen, through vibration produced in the anthers. The excess of rain during flowering and the lack of wind in the understorey of the forest constrain the effectiveness of the anemophily. However, several morphological characters of the flowers, leaf fall and dense clumps tend to expect for wind pollination. Also, the auto-incompatibility index (0.99) showed that M. riedeliana is an autocompatible bamboo. So the auto-incompatibility does not favour the formation of fruits in vegetal clones, and the autocompatibility could result in the high production of seeds. Therefore the possible occurrence of clones of M. riedeliana in the forest fragments, due to the effective vegetative growth and the 30-32 years cyclic flowering intervals, might explain the high investment on spikelets production and autocompatible fruits formation.
Semideciduous tropical forest; wind pollination; autocompatibility; vegetative growth; Merostachys
