"Unfortunately, many people now harvest plants indiscriminately as a source of income," it warns.
The WRC study, which focuses mainly on freshwater medicinal plants, was undertaken by independent researchers.
Among its findings is that over-harvesting of medicinal plants could leave millions without health care support.
"If South Africa’s medicinal plants experience continuous over-harvesting, millions of people will not have access to the premier health care service they provide in the near future."
The local trade in medicinal plants amounted to an estimated 20,000 tons a year, involving 574 species.
"An estimated 30 million people make regular use of the services of the country’s 200,000 traditional health care practitioners, all of whom apply indigenous and exotic plants in their remedies.
"This number excludes the people who purchase medicinal plants solely from informal markets."
The research team listed 230 medicinal plants that occur in South Africa’s freshwater ecosystems. The list includes many of the most important medicinal plants for local communities.
"These include annual herbs, aquatic (submerged and free floating) plants, ferns, geophytes, grasses, perennial herbs, sedges, shrubs, and trees.
"Medicinal plants [are] currently harvested at unsustainable rates in the wild... Since it is understood that the use of medicinal plants makes up an important part of African culture, authorities often turn a blind eye to over-harvesting."
The report calls for the establishment of regional "holding nurseries", where local traditional health practitioners and plant gatherers could obtain stock to propagate for their own use.