Guaiacum officinale, commonly known as roughbark lignum-vitae, guaiacwood or gaïacwood, is a species of tree in the caltrop family, Zygophyllaceae, that is native to the Caribbean and the northern coast of South America. Is one of two species yielding the true lignum vitae, the other being Guaiacum sanctum. Guaiac, a natural resin extracted from the wood, is a colorless compound that turns blue when placed in contact with substances that have peroxidase activity and then are exposed to hydrogen peroxide. Guaiac cards are impregnated with the resin and are used in determining whether stool contains blood. The heme portion of hemoglobin contains peroxidase and will catalyze the oxidation of guaiaconic acid when hydrogen peroxide is placed on the Guaiac card if blood is present in the stool.