Ethnopharmacology versus chemosystematics in the search for biologically active principles in plants.

The chemicals to which Brazilian angiosperms owe their use in the preparation of arrow poisons, hallucinogens, fish poisons, drugs, stimulants, spices, perfumes and pigments are correlated with the systematic position of the species in which they occur. Most compounds are produced either by the primitive Magnoliidae (sensu Cronquist) or by the advanced Asteridae. The Rosidae-Dilleniidae, precisely the group of subclasses of widest distribution over the country, have heretofore yielded relatively few useful compounds. This fact can be rationalized by the presence in their species of massive quantities of gallo- and ellagitannins, general defences which make the presence of specific alleochemics superfluous. The natural occurrence of specific biologically active compounds is thus ecologically and systematically conditioned and it should be possible to build a system capable of predicting the existence and the nature of useful chemicals in plant taxa.