Abstract:

Characteristics of the leaf epidermis of 8 species in the genus Caragana, which grow from the east to the west on the Ordos Plateau, were studied by observation through a light microscope (LM) and a scanning electron microscope (SEM). The study showed that the leaf epidermal cells were usually irregular or polygonal shaped, and the type of stomatal apparatus was mainly anomocytic. The stomatal density and the stomatal index of the xero-mesophytic C. purdomii were higher than these of the seven other xerophilous species (C. opulens, C. intermedia, C. korshinskii, C. roborovskyi, C. stenophylla, C. tibetica and C. brachypoda). Comparisons within species showed that C. intermedia, C. stenophylla, and C. tibetica had higher stomatal density when growing in heavier drought areas, whereas C. korshinskii had lower stomatal density; C. stenophylla and C. tibetica had a higher stomatal index whereas C. intermedia and C. korshinskii had a lower stomatal index. The leaf epidermis of C. intermedia, C. korshinskii, C. tibetica and C. roborovsky had a dense trichome, which was an adaptive characteristic caused by the droughty environment. The leaf epidermis of xerophytic species had a higher plasticity than that of mesophytic species. The plasticity index of C. stenophylla and C. tibetica, which are the dominant species in semi-deserts, was the highest among the 8 species. Observation using SEM revealed that there were two types of stomas: stomas located below the epidermal cells and stomas located on the same level with epidermal cells. It also revealed that there was cuticle and wax on the leaf epidermis, and that the trichome on the leaf epidermis was a single cell hair.

Key words: Ordos Plateau, Caragana, Leaf epidermis, Ecological adaptation