Leguminosae (legumes) are one of the largest plant families. They are widely used for a variety of purposes by people around the world and include many important cultivated economic food crops. On local scales, legumes are commonly used by various ethnic groups. However, the data are incomplete and scattered, not least in Thailand. We found that species of legumes were important in Karen communities, so we decided to investigate in detail the traditional knowledge of legumes on a local scale among Karen people in northern Thailand. We interviewed six herbalists and eighty-four nonherbalist informants in three Karen villages in Chiang Mai province about their use of legumes, and about the local names for the species, using semistructured interviews. A total of 83 legumes species (in 45 genera) had 4443 use reports. Five of the 83 legume species had not been reported previously as used in Thailand. Most Karen use reports (43%) of legumes were for food, medicine (36%), and materials (8%), but in term of species more legumes (68 species) were used for medicine than for food (53 species). The legume genera with most used species were Crotalaria and Flemingia each with six species. The most important species are Tamarindus indica (CI = 3.38), Senegalia rugata (CI = 2.39), Glycine max (CI = 1.27) respectively.

Ethnomedicinal studies have demonstrated that Fabaceae include the highest number of medicinal species of all plant families in Thailand. To evaluate which legumes hold the greatest potential for development of public herbal medicines, we used ethnobotanical indices to screen traditional medicinal species from 152 literature sources published from 1986–2019. The homogeneity of each use category was evaluated using the informant consensus factor (ICF). The popularity of the used species was evaluated by percentage of fidelity level (FL) and use value (UV). A total of 261 species from 98 genera of legumes were recorded for their traditional medicinal uses. The uses included 5387 use reports that covered treatments of 420 disorders. The ethnobotanical indices pointed to 15 species with high use values (e.g., Biancaea sappan (L.) Tod., Cassia fistula L., Senna siamea (Lam.) H.S.Irwin & Barneby). Nine of these species are already used in public herbal medicine. The other six species should be studied in greater depth, especially to identify their bioactive compounds so they can be developed for use in public herbal medicine.