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 Resaca del Rancho Viejo, 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 E. berlandieri Baill. ex Hemsl..