Green Grow the Lilacs is a folk song of Irish origin that was popular in the United States during the mid-19th century. The song title is the source of a folk etymology for the word gringo that states that the Mexicans misheard U.S. troops singing "green grow" during the Mexican–American War. The song appears in the 1931 stage play of the same name by Lynn Riggs, which is the basis of the 1943 musical Oklahoma!