Leaf Epidermal Morphology of Ten Wild Tree Peonies in China and Its Taxonomic Significance

Abstract

This research reports for the first time the epidermal characteristics of 10 wild tree peonies belonging to the sect. Moutan group. The leaf micromorphology of 10 wild tree peonies—P. qiui, P. decomposita, P. jishanensis, P. ostii, P. delavayi, P. lutea, P. potanini, P. rockii, P. ludlowii and P. cathayana—were investigated by light and scanning electron microscopy. The characteristics of the leaf epidermis were found to be constant at the species level, but variable among species. Patterns of anticlinal walls were slightly wavy to wavy, very wavy, and straight to curved. All studied tree peonies presented stomata only on the abaxial surfaces of the leaves. The stomatal apparatus was elliptical or rectangular. Stomatal density was highest on the abaxial surface in P. qiui (300.25 per mm2), and lowest in P. jishanensiss (198.41 per mm2). Stomatal Index was highest on the adaxial surface of P. potanini (27.30%), and lowest in P. ludlowii (18.35%). Trichomes were observed in four studied peonies, which appeared only on the abaxial surface of the leaves, and three basic types of trichomes were identified. The long conical trichomes were distinctive of P. jishanensis, and the flat-shaped trichomes were characteristic of P. qiui, P. rockii and P. cathayana, and commonly occurred in the intervenous region and leaf veins. Stomatal shape, stomatal density, anticlinal wall patterns and trichomes may be of great value and significance for the classification of wild tree peonies. The principal component analysis showed that the component 1, component 2 and component 3 were the most components and nearly 79% of the observed variation. The key to the identification of wild tree peonies based on trichomes and stomata diversity was provided.