Abstract: Leaf morphology of 29 Chinese species and one Thailand species of the Selaginellaceae was observed under light microscope and stereoscope. Species examined are rather consistent in leaf morphology. (1) Leaves are usually dimorphic, monomorphic only in few species, not petiolate, with the lateral leaves of the dimorphic leaf species larger than the median leaves, spreading outward or ascending, and the median leaves more or less adpressed on the adaxial side of stem, decussate or imbricate, and arranged in four ranks, while the leaves in the monomorphic leaf species spirally arranged. (2) The cells of the upper epidermis of the lateral and the median leaves are similar to each other, sub-isodiametric, tetragonal or oblong, and the anticlinal walls are straight, arched, sinuate or sinuolate; the cells of the lower epidermis of the lateral and the median leaves are also similar to each other, oblong or elongate, and the anticlinal walls are sinuolate. (3) The stomatal apparatuses, which are of anomocytic or actinoid types, are mainly distributed on the midvein region of upper epidermis of the median leaves and lower epidermis of the lateral leaves. The characters of the leaf macromorphology and of the micromorphology of the epidermal cells as well as the distribution patterns of stomata prove to be important for species delimitations in the Selaginellaceae. The studied species can be differentiated according to the following characters: (1) the shape of leaves (dimorphic vs. monomorphic); (2) the leaf arrangement (spiral vs. alternate); (3) the shape of the anticlinal walls (straight, arched, sinuate or sinuolate); (4) the shape of the cells of upper and lower epidermis (homomorphic vs. heteromorphic); (5) the type of the stomatal apparatus (anomocytic vs. actinoid); and (6) the difference in distribution of stomata on the upper and lower epidermis of the lateral and the median leaves.

Key words: Selaginellaceae, morphology, foliar epidermis, taxonomy, China.