Phlox divaricata is a widespread and variable species within a group of taxa noteworthy for geographic variation and hybridization. Pollination biology of this species is intriguing, and has not been adequately investigated. Because observed flower visitors are not necessarily sufficient pollinators, quantification of pollinator effectiveness has become an integral part of pollination biology studies, allowing a more accurate interpretation of the effects of pollinators on plant floral and reproductive traits, the distribution of individuals, population dynamics, and phylogeography. Phlox divaricata has a wide geographical distribution, with the Central Plains representing the westernmost portion of its range, where P. divaricata occurs in scattered populations on rich slopes and creek bottoms. This study focused on the tallgrass prairie of the Central Plains. Visitors to P. divaricata were identified using caging and observation to determine diurnal, crepuscular, and nocturnal visitors and their effects on seed set. Additional studies were conducted to document the breeding system of P. divaricata and its pollen threshold. To look for shifts in pollinator types across geographic regions, surveys of P. divaricata populations along latitudinal and longitudinal transects were compared. These results lay the foundation for experimental studies on the effectiveness of individual visitors to P. divaricata.

Key words: Central Plains, mating system, Phlox divaricata, pollen threshold, pollination biology