Ecological Anatomy of the Root in Bretschneidera sinensis,a Threatened Endemic Plant in China

Bretschneidera sinensis is a rare endemic and tertiary relict plant of China.Its structural and epidermis micro-morphological characteristics were studied by paraffin section,scraping section and scanning electron microscopy (SEM).Results showed that the epidermal cells were covered with a thin cuticle layer,the cell shape was irregular and the patterns of anticlinal walls were sinuolate.The upper epidermis was covered with barred wax and the sunken stomatas only presented on the lower epidermis,which was surrounded by flowerlike neurite structures.Mesophyll tissue included onelayer of palisade tissue,accompanied with multilayers of welldeveloped spongy tissue containing secreting cells with myrosinase and crystals cells.Significant changes in leaf thickness,ratio of spongy to palisade tissue thickness (S/P),and volume of chloroplast were presented in the different phases and zones,indicating a special change from sciophytes to mesophytes during the growth process.The close relationship between Bretschneideraceae and Sapindaceae was supported from the flowerlike neurite structures found in the abaxial epidermis (similar to Sapindaceae), while differences showed the independence of Bretschneideraceae in Sapindales as a family.