Abstract: Leaves of 25 species which cover 13 genera of the Chinese Hamamelidaceae (sensu lato ) were examined by light microscope (LM) and scanning electron microscope (SEM) to reveal the nature and variation of trichomes. The trichomes showed greater diversity under SEM than under LM and naked eyes. Based on Theobald’s scheme, they can be divided into four types: 1. Simple trichomes: Unbranched, curved or straight (Altingia, liquidambar, Semiliquidambar; 2. 2- 4 armed trichomes: Two to four branched (Corylopsis, Loropetalum, sinowilsonia); 3. Stellate trichomes: With more than five branches. They may be tufted (Forthunearia, Loropetalum, sinowilsonia, Hamamelis, Distylium) or storied (Eustigma); 4. Scales: Peltate and flattened. In the genus Rhodoleia, the scales are totally composed of small boat-shaped ones, whereas in the genus Sycopsis they are rotately branched on the verge but unbranched and flattened in the middle. The distribution of trichome types is of grest significance in hamamelidaceous phylogeny. The simple trichomes mainly exist in Liquidambaroideae and Exbucklandioideae, the stellate and 2-4 armed trichomes occur in Hamamelidoideae, and the scales are confined to Sycopsis (Hamamelidoideae) and Rhodoleia (Rhodoleioideae). From this fact, the authors consider that there are two evolutionary lines in the family, i. e. the Disanthoideae- Exbucklandioideae- Liquidambaroideae line and the Rhodoleioideae-Hamamelidoideae line though some subfamilies are isolated. Within Hamamelidoideae, the trichome types also have taxonomic significance. Corylopsis is a primitive group, whereas Eustigma, Distylium and Sycopsis are respectively on the top of evolutionary branches and the other genera are transitional groups. These genera might be separated as tribes, Corylopsideae, Eustigmateae, Distylieae, Sycopsideaeand Hamamelideae. The relationships among these tribes are given in Fig. l.

Key words: Hamamelidaceae, Trichomes, Micromorphology, Phylogeny