Mangosteen is a tropical fruit tree and has over 40 naturally occurring xanthones and the pericap has the richest concentration of these xanthones. Keep in mind that xanthones occur in only a very limited way in nature and this rich source of xanthones is what makes mangosteen unique. It is also important to note that mangosteen is a rich source of naturally occurring minerals, enzymes, vitamins, phytonutrients and bioflavanoids as well.