Cohen et al. found that samples of brands sold in American brick-and-mortar stores contained highly variable amounts of yohimbine, and sometimes none at all. Labelling claims were often misleading. Similar results have been reported by other laboratories for products sold in the U.S., in other countries and on the internet. One study found that many brands of "yohimbe" might not derive from the "P. johimbe" tree in the first place. According to yet another source the yohimbe sold in markets in West Africa, where the tree grows, is frequently adulterated with other species of the genus "Pausinystalia"; these contain little yohimbine. The amounts of alkaloid found even in genuine "P. johimbe" bark vary considerably, depending on the source of the bark (roots, stem, branches, height, etc.).