Background: Wild plants are one of the plant resources that have contributed most to meet the basic needs of human and are essential for the livelihoods of various peoples of the world. In addition, they represent a priority resource in periods of food shortages, especially for the populations in developing countries. Thus, this study aimed to know the wild plants food species diversity and its subcategories of use in emergencies and/or nonemergencies situations in four rural communities of the Semiarid Region of Piauí state, Brazil.Methods: Wild food species on Carrasco vegetation in rural communities of the Semiarid Region of Piauí state, Northeastern Brazil were documented evaluating whether there is a consensus among the informants regarding the knowledge associated with the subcategories of food use and also analyzing whether ecological factors, age and gender behaved as variables that influenced the knowledge, selection and/or use of these species. For data documentation, 93 interviews through semistructured forms were performed and the participant observation technique was applied.Results: Forty-three food species of emergency use, thirty-sixth for non-emergency use, twenty-eighth subcategories of food use were cited by interviewees, and a consensus related to this knowledge was registered. In the four rural communities studied there was not positive correlation between age and the number of known plants, while the number of species known by men and women in Oiticica rural community diverged significantly, differing from the findings in Bebedouro, Itapecuru, and Pinga. The ecological factors studied influenced the selection and use of the known wild food species in these communities.