Leaf-morphology and leaf-anatomy in Ephedra altissima D_esf. (Ephedraceae, Gnetales) and their evolutionary relevance

Abstract

Leaves in most extant Ephedra -species represent only rudimentary scales without chlorophyll. Photosynthesis is completely restricted to green shoots. Only some species, e.g. Ephedra altissima, develop folious leaves even when being mature. Morphology and anatomy of cotyledons, primary leaves, and subsequent folious leaves of Ephedra altissima were examined particularly with special focus on their vasculature. The results show that the reduction of the leaves is achieved by an extreme reduction of the adaxial leaf surface. Most parts of the leaf surface are therefore developed by the abaxial side. Apart from a reduced lamina, a thick cuticle and sunken stomata are the only xerothermic adaptations in leaves of Ephedra altissima. A hypodermis and endodermis are also not developed. The anatomical results indicate that ancestors of modern Ephedra- species might have evolved in a more humid climate, contrasting to the arid habitats in which extant Ephedra- species are native today.