Leaf Epidermal Morphology and Systematic Significance of Genus Heracleum in Southwest China

Leaf epidermis characters in 16 species 1 variety(belonging to all the four sections) of Heracleum(Apiaceae) in SW China were investigated using light microscopy(LM) and scanning electron microscopy(SEM).The stomatal size,density and index were measured,and the statistical t-test method was used to ascertain the significant level of the differences in the stomata of each species.It was shown that the stomata were anomocytic and existed on the abaxial epidermis in all the species examined,and on the adaxial epidermis in a few of species.The length and density of the trichomes vary with the species and presented on abaxial epidermis of most studied species and on the adaxial epidermis of some species.The adaxial epidermis cells were usually irregular or polygonal in shape with anticlinal walls straight,repand,or sinuous,and the epidermal of abaxial epidermis cells were usually irregular in shape with anticlinal walls repand,or sinuous.Under SEM,the inner margin of the outer stomatal rim was nearly smooth,repand or erose,and the cuticular membrane of the leaf epidermis was stripe,covered with granular or squamose wax.The types of outer stomatal rim and wax were reliable characters to identify some species.These data of leaf epidermis of Heracleum demonstrated that there are many distinct characters among the species.We discussed the systematic and evolution significance of leaf epidermis,and a dichotomous key of Heracleum according to leaf epidermis characters was also compiled in this paper.