Inflorescence type and design determine the position of reproductive meristems and sequence of flowers opening. I examined the gender expression over two entire flowering seasons in Sedum praealtum A. DC. (Crassulaceae) in Central Veracruz, Mexico. Specifically, I studied the floral longevity, sexual-phase duration, flower opening within an inflorescence and sex ratio in the species. I observed that the 8-days flower initiated in male-phase and then switched to female-phase. An extended time of pollen presentation by gradual anthers dehiscence caused an incomplete protandry in the species. The basal-positioned floral buds reached anthesis sooner than the distal-positioned floral buds, resembling an acropetal flowering sequence. Inflorescences production ceased in the middle of the flowering season, whereas flower opening remained constant over reproductive season of the species. The opening of flowers in successive cohorts linked to changes in the flower sexual-phase phenology caused an initial sex expression toward maleness and a balanced sexual expression from the peak to the end of reproductive season in the population sampled. This study highlights the important influence that variations in onset and duration of sexual-phase of flowers can have on sex expression in flowering plants.
Dichogamy, incomplete protandry, sexual-phase, sex ratio, stonecrop