Guaiacum officinale, commonly known as roughbark lignum-vitae,[3] 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.

[2] This small tree is very slow growing, reaching about 10 m (33 ft) in height with a trunk diameter of 60 cm (24 in).

The blue flowers have five petals that yield a bright-yellow-orange fruit with red flesh and black seeds.

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.

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.