Resumen:

Cuticle micromorphology and stem anatomy of the two Ecuadorian species of Ephedra L. (Ephedraceae): E. americana Humb. & Bonpl. ex Willd. and E. rupestris Benth. were studied using thin sections and SEM. Historically these two taxa have been treated as varieties of E. americana by Stapf (1889). As part of a revision of New World Ephedra, this study was undertaken to clarify their taxonomic status. Differences were found in the distribution of stomata and papillae, shapes of epidermal cells, amount and distribution of fibers. Abundant papillae are found on the outer cuticular surface in E. americana, while they are absent from E. rupestris. Epidermal cells in non-stomatiferous regions are polygonal in E. americana and rectangular in E. rupestris. Sclerification of the stem is accomplished by lignified hypodermal and cortical fibers in E. rupestris, while the fibers are merely composed of cellulose in E. americana. E. americana is further characterized by having stomata in rows confined to stomatiferous furrows. In contrast, E. rupestris displays an ill-defined arrangement of stomata, lacking sharp furrows and ridges. There seems to be a correlation with stomatal characters and habitat. E. rupestris occurs predominantly in the shrub and cushion páramos, while E. americana is found in the lower valleys of the inter-Andean desert. These characters in combination with some characters of the strobili substantiate the distinctiveness of the two species.