Guayusa is a tree of the holly genus, native to the Ecuadorian Amazon rainforest. It is a distant relative of both Yerba Mate and Yaupon Holly (the plant used to make the "black drink"). The leaves have the highest caffeine content of any known plant. It is commonly consumed as a morning ritual in the Ecuadorian rainforest. It has a stronger, earthier taste than Yerba Mate.