XVI International Botanical Congess
The paucity of taxonomic characters that have been used to circumscribe sectional and subsectional groups in New World Ephedra presents a challenge to systematic study. Seed and stem cuticle of 14 species representing the four subsections native to the United States and Mexico were examined with SEM. Considerable variation was found in seed size, shape and surface features and stem cuticle. Subsection Trifurcae is characterized by ovoid seeds with an attenuated apex. Species differ in abundance and shape of papillae. Subsections Asarca, Antisyphiliticae and Americanae have ellipsoid to globose seeds but delineation of these subsections on seed characters alone is not possible. However, in all subsections cuticle micromorphology of stems is taxonomically useful. Significant features include stomatal bands, surface papillae, stomatal opening, epidermal cell size and shape.