POLLINATION BIOLOGY OF HESPERALOE-PARVIFLORA

The pollination biology of Hesperaloe parviflora (Agavaceae) was studi ed in a natural population at Dolan Falls in south-central Texas. The red tubular flowers varied greatly in tube length and width, mouth wid th, and in relative positions of stigma and anthers. Flowers opened ar ound dawn, and closed around noon; individual flowers lasted for 1 day , while the flowering period for plants was estimated to last 15 to 25 days. Compatibility experiments showed complete self-incompatibility. Black-chinned hummingbirds (Archilochus alexandri) were exclusive vis itors to the flowers, and pollen deposition on stigmas was confirmed. Visits occurred either as part of male territorial trapline flights, o r in conjunction with female birds feeding on nearby Fouquieria splend ens flowers. Analysis of pollination biology within H. parviflora and other members of Hesperaloe, which is closely related to Yucca, may pr ovide information to further understanding of the evolution of the obl igate pollination mutualism between yuccas and yucca moths.