Abstract: Anatomical observation of aerenchyma helps understand the growth,distribution,and adaptation of wetland plants to different habitats.Anatomical structures of the stem and leaf were carefully studied,using optical microscope and paraffin section technology,in four dominant wetland species(Miscanthus sacchariflorus,Phalaris arundinacea,Carex argyi and Polygonum hydropiper) distributed along a water-level gradient in Dongting Lake.Results showed that the stem aerenchyma was formed from three tissues,i.e.cortex,vascular bundles and the medullary cavity.Among them,the medullary cavity was the primary tissue for aerenchyma formation,accounting for more than 77%.The size of the stem aerenchyma from highest to lowest was:Polygonum hydropiper(57.8%)>Carex argyi(45.5%)≥Phalaris arundinacea(41.7%)≥Miscanthus sacchariflorus(37.8%).Leaf aerenchyma in Miscanthus sacchariflorus and Phalaris arundinacea was formed in the vascular bundles,Polygonum hydropiper in the mesophyll tissue,and Carex argyi in both mesophyll tissue(99%) and vascular bundles(1%).Leaf aerenchyma of Carex argyi was highly developed,with a size of 33.8%.The other three species had relatively undeveloped leaf aerenchyma,with a size of only 0.13%-1.68%.Except for Phalaris arundinacea,the aerenchyma size was consistent with the sites of field distribution in Dongting Lake.These data indicate that the aerenchyma of wetland plants is closely related to its distribution.