Abstract
While different biosynthetic groups of secondary metabolites (micromolecules) rarely accumulate in the same plant species, one such group may replace another in morphologically related taxa. The use of micromolecules as general systematic markers of the plant kingdom thus requires unifying postulates concerning their evolution patterns. Two such postulates — contraction of the shikimate pathway and blocking of oxidative enzymes — are illustrated with the aid of systematic considerations on the genera Aniba (Lauraceae) and Derris-Lonchocarpus (Leguminosae) which involve besides chemistry, morphology, ecology and geography. Extrapolation of the principles applied in these examples to the entire plant kingdom seems possible, an important fact, due to the ecological implications of micromolecules. In this sense, the paper opens the way, rather than simply to a more "natural" classification, to an information retrieval device of ecologically relevant facts about plants.