Abstract: Hamamelids have a long fossil history and an important fossil record. Their interesting biogeographic relationships indicate a great age. There exist good surveys of the pollen and floral organs of this family whereas it is so far poorly known from leaf architecture. The leaf architecture of all 29 genera with more than 60 among the total of 140 species of the family was surveyed in this work using clearified leaves. It is found that leaf architecture analysis may shed light on the relationships within the family and the conclusion of evolution based on leaf architecture basically accords with that based on others. The major categories of leaf architecture of Hamamelids observed in this work are as follows: leaf form, leaf margin, tooth type, venation, marginal ultimate venation, areolation and trichome. It must be emphasized that of all these characters the tooth type is the most stable and useful for systematics. In this work a new tooth type is recognized under the name altingioid. Teeth of this type are obviously asymmetrical, with a persistent transparent gland on the top, and with their lateral veinlets free, not reaching the medial vein. All three genera of the subfamily Liquidambaroideae have this tooth type, whereas most leaves of the rest genera of this family have fothergilloid teeth, which are basically symmetrical, without glands. The venation in the fothergilloid tooth is almost the same as that in the altingioid tooth, the only difference being that the lateral veins on the abaxial side of the altingioid teeth are usually absent or very weak and short if present. The present authors consider that the subfamily Liquidambaroideae has to be separated from the family Hamamelidaceae sensu lato and treated as an independent family, Altingiaceae, on the basis of the special tooth type. different pollen morphology and flower structure. The stability of tooth type may serve classification not only of order and family level, but also of tribe, genus and species level with the help of characters of teeth, such as shape, size, density, distribution, single or double, with or without glands. By comparison of Hamamelidaceae and Altingiaceae with some primitive families of subclass Hamamelidae, namely, Trochodendraceae, Tetracentraceae, Cercidiphyllaceae, Eupteleaceae and Platanaceae, the putative evolutionary trend of tooth types is outlined as follows: ↑ altingioid Chloranthoid → Cercidiphylloid →platanoid → fothergilloid In general evolutionarytrend of teeth within these families is reduction and simplification in structure.

Key words: Hamamelidaceae, Leaf architecture, Systematics.