Karwinskia humboldtiana, commonly known as coyotillo or Humboldt coyotillo, is a species of flowering shrub or small tree in the buckthorn family, Rhamnaceae. It is native to southern and western Texas in the United States as well as much of Mexico. The seeds and leaves of this plant contain the quinones eleutherin and 7-methoxyeleutherin and chrysophanol and β-amyrin in the fruits that are toxic to humans and livestock.