Catechu and tannic acid are plant-derived tannins. Catechu comes from the leaves of Uncaria gambier and consists of dried aqueous extract containing tannins like catechins. Black catechu comes from the heartwood of Acacia catechu and Acacia chundra. Tannic acid is obtained from nutgalls, which are outgrowths on oak tree twigs, and yields gallic acid and glucose upon hydrolysis. Both catechu and tannic acid are used as astringents.