Source Naturals Pau D'Arco is the highest quality inner bark of the Purple Lapacho tree found in Brazil and Northern Argentina. Ever since ancient times, when it was a standard for the medicine men of the Inca Empire, pau d'arco (also known as ipe roxo and taheebo) has been one of the most widely used herbs in South America. Its popularity is attributed to the active constituent, lapachol, which has been the subject of numerous scientific studies.