One of the most important sources of pau d’arco inner bark and heartwood is T. impetiginosa (Fig. 1), a large tree up to 30 m tall, with deep pink to purple flowers, found from Mexico and Central America to tropical South America south to northern Argentina and Bolivia. Significant also is the large tree T. rosea, with pink to purple flowers, found from Mexico to northern South America, and T. serratifolia (Fig. 2), having yellow flowers, which occurs from Colombia to the Guyana and south to Brazil and Bolivia. These and a majority of the remaining 23 species of Tabebuia tested contain lapachol or related compounds, each with varying concentrations in the inner stem bark, heartwood, and leaves.