Esenbeckia runyonii is a species of flowering tree in the citrus family, Rutaceae, that is native to northeastern Mexico, with a small, disjunct population in the Lower Rio Grande Valley of Texas in the United States. Common names include Limoncillo and Runyon's Esenbeckia. The specific epithet honors Robert Runyon, a botanist and photographer from Brownsville, Texas, who collected the type specimen from a stand of four trees discovered by Harvey Stiles on the banks of , Texas, in 1929. Conrad Vernon Morton of the Smithsonian Institution received the plant material and formally described the species in 1930. Some consider it a synonym of Baill. ex Hemsl..