Leaf Epidermal Morphology of Lasianthus (Rubiaceae) and Its Related Genera in Asia

Leaf epidermal morphology of 26 species(including 1 subspecies and 2 varieties)of Lasianthus and 6 species of its related 4 genera Morinda,Psychotria,Saprosma and Urophyllum,were investigated under both light microscope(LM)and scanning electron microscope(SEM).It was shown that the shapes of upper leaf epidermal cells varies from irregularly sinuolate,nearly elliptic to irregularly polygonal.The lower leaf epidermal cells are usually irregularly sinuous or sinuate.The patterns of anticlinal walls are sinuate irregularly,and the ambits are inconspicuous between the cells.It was found that the cell walls of both upper and lower epidermis are covered with thick corticle.Under SEM,the cuticula membrane of the leaf epidermis is distinct,and granular,reticulate,scaly or papilliform in shape.The stomatal apparatus is of paracytic type and occurs only on the lower surface.The stomatas of some species are sunken.Leaf indumentum of Lasianthus species can be classified into single-celled hairs and uniseriate multi-celled hairs including linear,twisted and straight-walled hairs.The leaf epidermal morphology of the related genera in Rubiaceae is similar to Lasianthus.In conclusion,the leaf micro-morphological characteristics have some significance in identification of Lasianthus species,but show regular variation with habitats.The variations of the ratio between stomatal polar axis and outer stomatal ledge aperture,as well as leaf indumentum of Lasianthus species are well correspondent to their habitats.