Abstract: Light and scanning electron microscopes were used to examine foliar epidermal features such as the shape of epidermal cells, the type of stomatal apparatus and outer stomatal rim in 38 species of 6 genera of the Betulaceae. Four types of stomatal apparatus on mature leaves are recognized in this survey: anomocytic, cyclocytic, non-typical actinocytic and brachyparacytic. The foliar epidermal characters and character states are taxonomically useful for the identification of genera and the division of tribes. The generalized evolutionary scheme for foliar epidermal features is fairly closely correlated with the generic relationships proposed in other studies (Abbe, 1935, 1974; Brunner & Fairbrothers, 1979; Hall, 1952; Kikuzava, 1982; Kuprianova, 1963)and it is clear that foliar epidermal morphology can be an important taxonomic character added to others for determining evolutionary relationships. The explanations of generic relationships are based on our hypothesis that anomocytic stomatal apparatus, uni-layered outer stomatal rim, having not T-pieces at the polar region of guard cells and straight anticlinal wall of lower epidermal cell are from the ancestor (Fig. 1). Sinuolate or sinuate anticlinal wall of lower epidermal cells and non-typical actinocytic stomatal apparatus, present in Corylus, Ostryopsis, Ostrya and Carpinus of the Betulaceae, correlates with the separation of Coryleae from Betuleae. Betuleae including Alnus and Betula is considered primitive with more primitive characters. Of Coryleae, Carpinus might be the most advanced, with brachyparacytic

stomatal apparatus and double-layered outer stomatal rim.

Key words: Betulaceae, stomatal apparatus, Foliar surface features