Re-examining hypotheses concerning the use and knowledge of medicinal plants: a study in the Caatinga vegetation of NE Brazil

BACKGROUND: The Caatinga (dry land vegetation) is one of the most characteristic vegetation types in northeastern Brazil. It occupies a large percentage of the semi-arid region there, and generally supports two major types of economic activity: seasonal agriculture and the harvesting of plant products. However, very little information is available concerning the interaction of people with the plants of the Caatinga. METHODS: A study was undertaken with the participation of 31 adults from a rural community in the state of Pernambuco, Brazil, in order to analyze the patterns of use of medicinal plant resources, and to test a number of hypotheses concerning their use and local knowledge about them. The sources of medicinal plants used by the local community, the differences in oral information concerning the use of plants with their effective uses, and the role of exotic plants in local folk medicine practices were examined. RESULTS: Forty-eight plant species were cited as having medicinal uses, of which 56.25% are native to the Caatinga region. The patterns of harvesting and the importance of these trees and shrubs as medicinal plants seem to be compatible with a hypothesis based on the seasonal availability of plant resources. There is no direct correlation between known medicinal plants and those used by the local population, which agrees with observations made in different tropical regions. However, this observation was not interpreted in terms of the idea of "erosion" of knowledge (commonly used to explain this lack of correlation), but rather to propose two new concepts: "mass knowledge" and "stock knowledge". CONCLUSION: Native plants are a very significant component of locally used medicinal plants, although exotic plants are important for treating specific health problems – which leads the proposal of a hypothesis of diversification.