XVI International Botanical Congess

Morphological characteristics and resource allocation in the dispersal units of eight tropical perennial grasses belonging to tribe Andropogoneae were investigated. The dispersal units are diads, comprising a sessile (fertile) and a pedicelled (sterile) spikelet. These grasses place a high premium in the enclosure of seed or in appendages as weight of husk or appendages (awn or sterile part) exceed the weight of seed except in Bothriochloa pertusa and Vetiveria zizanioides. For example, in Heteropogon contortus, awn accounts 62%, while caryopsis, husk of caryopsis and sterile spikelets contributed 15, 11 and 12% respectively towards total diad weight. Caryopsis contribution varied from 15 to 48%. Sterile spikelet accounts c. 30% in Andropogon gayanus, Chrysopogon fulvus and Sehima nervosum. Spikelet morphology was found to play a significant role in reproductive biology. Secondary metabolites present in seed enclosing envelope possibly played an important allelopathic role in protecting the seed from micro-organism and predators so as to keep a seed viable for a longer period in a natural ecosystem.