The pollination ecology of Opuntia cf. macrocentra (Cactaceae) in the Trans-Pecos Region of Texas

The present study was designed to examine the pollination ecology of populations of Opuntia cf. macrocentra throughout the Trans-Pecos region of Texas. Floral phenology was also investigated. The behaviors of insects that visited flowers were monitored and representatives were captured for identification. Breeding system tests were performed on plant specimens collected throughout the Trans-Pecos in the Sul Ross State University greenhouse complex and Opuntia garden. Fruit and seed sets from these tests were determined. Pollen morphology was examined for each population of Opuntia cf. macrocentra.;Like other Opuntia species, Opuntia cf. macrocentra flowers are diurnal. Flowers last only one day, unless inclement weather prevents or delays opening, in which case flowers may fully open on a second day. It is unclear whether temperature or sunlight influences anthesis more strongly. Anthers dehisce in the morning, within a few hours of anthesis. Stigmas are receptive in the afternoon; receptivity may be accompanied by a color change. Floral tepals change color as they age.;Numerous Carpophilous beetles were observed consuming floral parts and mating in flowers. No beetle contact with the stigma was observed, therefore beetles are not thought to be significant pollinators of O. cf. macrocentra. Foraging ants were observed gathering pollen and traveling up and down the style, but they did not deliver pollen to the stigmatic surfaces. Bees often visited flowers of O. cf. macrocentra and were observed both collecting pollen and landing upon stigmatic surfaces. Comparison of pollen taken from their bodies with pollen from anthers demonstrated them to be effective carriers of O. cf. macrocentra pollen. In the current study, bees were found to be the most significant pollinators of O. cf. macrocentra.