Mentawai people have a unique agricultural tradition. The traditional agricultural system (mone) is adaptive, using the plants that are suitable for the landscape. Land clearing is carefully done without destroying the entire forest. We conducted ethnobotany studies to explore the composition and the structure of the plants used in the traditional plantation (Pumonean) as well as their values for the Mentawai people in the Siberut island. We surveyed the agricultural system employed by Mentawai people and conducted vegetation assessment in the study sites. The data on the plant species and land usages were gathered from interviews with key informants in the areas. We analyzed the data using Local User's Value Index (LUVI). The plants were collected to aid with species identification and were stored at the Andalas University Herbarium (ANDA), Padang. Throughout the study, we recorded 64 species in 27 families. Euphorbiaceae was the family with the highest species diversity. Sagu (Metroxylon sago) was the species with the highest LUVI. We categorized the land usage for the traditional plantation into four categories, consisting of wetland, the edge of wetland, mixed plantations (mone), and forests (leleu). The mixed plantation was the category with the highest LUVI. Beside the traditional agricultural system, the Mentawai people also developed a more modern agricultural system. For the traditional system, Durio zibethinus was the species with the highest importance indices, whereas for the more modern system Theobroma cacao was the species with the highest importance indices.