In comparison with terrestrial plants, those growing in wetlands have been rarely studied ethnobotanically, including in China, yet people living in or near wetlands can accumulate much knowledge of the uses of local wetland plants. A characteristic of wetlands, cutting across climatic zones, is that many species are widely distributed, providing opportunities for studying general patterns of knowledge of the uses of plants across extensive areas, in the present case China. There is urgency in undertaking such studies, given the rapid rates of loss of traditional knowledge of wetland plants as is now occurring.
There have been very few studies specifically on the traditional knowledge of wetland plants in China. However, much information on such knowledge does exist, but dispersed through a wide body of literature that is not specifically ethnobotanical, such as regional Floras. We have undertaken an extensive study of such literature to determine which species of wetland plants have been used traditionally and the main factors influencing patterns shown by such knowledge. Quantitative techniques have been used to evaluate the relative usefulness of different types of wetland plants and regression analyses to determine the extent to which different quantitative indices give similar results.
350 wetland plant species, belonging to 66 families and 187 genera, were found to have been used traditionally in China for a wide range of purposes. The top ten families used, in terms of numbers of species, were Poaceae, Polygonaceae, Cyperaceae, Lamiaceae, Asteraceae, Ranunculaceae, Hydrocharitaceae, Potamogetonaceae, Fabaceae, and Brassicaceae, in total accounting for 58.6% of all species used. These families often dominate wetland vegetation in China. The three most widely used genera were Polygonum, Potamogeton and Cyperus. The main uses of wetlands plants, in terms of numbers of species, were for medicine, food, and forage. Three different ways of assigning an importance value to species (Relative Frequency of Citation RFC; Cultural Importance CI; Cultural Value Index CV) all gave similar results.
A diverse range of wetland plants, in terms of both taxonomic affiliation and type of use, have been used traditionally in China. Medicine, forage and food are the three most important categories of use, the plants providing basic resources used by local people in their everyday lives. Local availability is the main factor influencing which species are used. Quantitative indexes, especially Cultural Value Index, proved very useful for evaluating the usefulness of plants as recorded in the literature.