In this communication, we provide some basic methodological and practical ideas for plant knowledge comparisons among different predefined natural regions of the Mediterranean island of Mallorca, in the frame of an ongoing project in this area. The final goal of this work is to present a tool to find out to what extent plant knowledge is similar in the different regions. We use an uncommon approach to ethnobotanical studies in terms of multidisciplinary methodology. We base our arguments on social anthropology methods, using a diversity index (the Sorensen similarity coefficient), and we also explain the botanical part of the investigation. Our preliminary results reveal few differences among the three natural regions considered on the island, which we believe could find their explanation in geographic, botanical and cultural aspects.