1 Floating Plants Among the floating plants commonly used in constructed wetland systems, there are water hyacinth, giant knotweed, water dropwort, duckweed, water spinach and watercress. According to the analysis of the botanical characteristics of these plants, it is found that they have the following characteristics: ① strong vitality, good adaptability to the environment and developed roots; (2) Large biomass and fast growth; (3) Seasonal dormancy, such as water hyacinth, water hyacinth and water spinach which are dormant or dead in winter, and water dropwort and watercress which are dormant in summer. The vigorous growth season is mainly concentrated in March 3- 10/0 or September-May of the following year; ④ The growth cycle is short, mainly vegetative growth, and the demand for N is the highest.

2 roots, bulbs and seed plants These plants mainly include water lily, lotus, calla lily, arrowhead, water chestnut, taro, Alisma orientalis, water chestnut, coix seed, Euryale ferox and so on. They have developed underground rhizomes or tuberous roots, or can produce a large number of seeds and fruits, mostly seasonal dormant plants, which generally wither in winter and germinate in spring, and the growing season is mainly concentrated in April-September.

Three kinds of emergent herbs: including reed, POTAMOGETON crispus, Typha Typha, Phyllostachys praecox, Pennisetum, Allium fistulosum and Cyperus esculentum. It is the main plant selection variety in constructed wetland system. The common characteristics of these plants are: ① strong adaptability, or local dominant varieties; ② The root system is developed, the growth is large, the vegetative growth and reproductive growth coexist, and the absorption of N, P and K is rich; ③ It can grow in soilless environment.