Papilionoideae is a subfamily of flowering plants that includes thousands of species. Synonyms for Papilionoideae include the Fabaceae or the Leguminosae family. Members of this subfamily have characteristic butterfly-shaped flowers and produce pods or legumes as fruit. Some commonly known plants in this subfamily include peas, beans, and soybeans. The Fabaceae family is incredibly diverse, with species growing as trees, shrubs, and herbs. These plants play important roles in agriculture, medicine, and the environment. As legumes, they also have the ability to fix nitrogen, which is an essential nutrient for plant growth.