Reproductive ecology of Uapaca kirkiana (Euphorbiaceae) in Malawi, southern Africa

The dioecious character (sex ratios and stand structures, conspecific neigh bour relationships, inflorescence numbers and structure) and reproductive p rocess (phenology, anthesis, flower visitors and fruit production) of a mio mbo woodland species, Uapaca kirkiana were investigated in natural populati ons in Malawi. The sex ratio of reproductive individuals greater than or eq ual to 10 cm diameter at breast height was about 1:1 and departures from th is ratio mostly resulted from a higher proportion of the males. Spatially, the sexes were randomly distributed but generally within 10 m of each other with no obvious gender differences in size. Throughout Malawi, male and fe male reproductive individuals flower synchronously between October-April (w ith a peak period in February-March). A 6: 1 male to female inflorescence s ex ratio was common. Anthesis in female inflorescences lasts almost twice a s long as in male inflorescences and only the latter have any odour. On mal e trees, inflorescences are in fascicles, whereas on female trees, they are solitary. In both cases, the infloresences are generally similar in size e xcept for the peduncles of the male inflorescences which are longer than th e female's. A range of insects visits U. kirkiana flowers but the most like ly pollinators are bees (Apis mellifera), and beetles (Dothera bennigseni, Chelomenes lunata, Alcidodes denticulatus and Mitracamenta sp.). Apart from pollen from the male inflorescences, female flowers do not offer any obvio us reward for flower visitors. Pollination studies revealed that assisted p ollination did not significantly improve fruit production or seed quality o ver unpollinated or naturally pollinated inflorescences. Facultative agamos permy (apomixis) is suspected as a phenomenon requiring further attention i n U. kirkiana.