Asymmetrical development of biovulate cones resulting in uniovulate cones in Ephedra rhytidosperma (Ephedraceae)

Female cone morphology in Ephedra, including the number of initiated ovules and mature seeds per cone, provides important taxonomic characters used in sectional or species delimitation within Ephedra. Recent molecular phylogenies have indicated, however, that seed number per cone has changed repeatedly during the evolution of the genus. This study reports on the development of the female cone of E. rhytidosperma, based on a large sample of dissected cones studied under SEM. All cones were initially biovulate, and in the majority of cases, both female reproductive units (FRUs) developed a micropylar tube and formed mature seeds. In a few cases, the FRU pair developed asymmetrically in a cone, with one of them eventually aborting. There was no evidence of fusion of the FRU pair. Phylogenetically, E. rhytidosperma is in a clade with E. equisetina, which has uniovulate cones, and E. gerardiana and E. minuta, which have biovulate cones that also become unispermous via abortion. The biovulate condition may thus be ancestral in this clade.