A Biophysical Perspective on the Pollination Biology of Ephedra nevadensis and E. trifurca

Abstract

Previous research indicates that Ephedra nevadensis S. Wats. and E. trifurca Torr. Ex S. Watts are capable of capturing airborne pollen because of (1) the absence of foliage obstructing airflow, (2) the streamlined geometry of ovules, (3) the orientation of ovules with respect to the vertical, (4) the clustering of ovules, and (5) wind-induced oscillations of stems and pollination droplets. Wind tunnel studies and computer models also show that slightly inclined stems deflect and funnel airborne pollen upward along their leeward sides toward ovules. Additionally, the dimensions, settling velocities, and other features of Ephedra pollen in theory are compatible with long-distance wind dispersal of pollen. These features increase the efficiency of wind pollination and are consistent with anemophily. However, none of these features precludes alternative pollination mechanisms, as for example the deposition of pollen by insects foraging pollination droplets. A biophysical perspective indicates that these Ephedra species are capable of being wind pollinated but it cannot preclude the possibility of insect pollination.