CHEMOSYSTEMATISCHE BETRACHTUNGEN ZUR GROSSGLIEDERUNG DER DICOTYLEN

Summary It is almost unanimously agreed that the Ranales s.l. (= Polycarpicae) constitute the universal basic group for at least all dicotyledons. Cronquist, for example, derives from them the two principal lines of his system, his Rosalean branch and his Guttiferalean branch. Attention is called to the fact that phytochemical evidence is inconsistent with such a view: some alkaloids highly characteristic for the Polycarpicae (protoaporphines, aporphmes as well as berberin and other quaternary bases) are absent from both the Rosales and the Guttiferales. They are present, however, in the Rutaceae, other chemical as well as morphological features of which support the conjecture of a direct link with the Polycarpicae. On the other hand, the Rosalean and Guttiferalean branches (at least their more primitive members) coincide in the possession of biogenetically obviously related trihydroxylated phenolic substances like ellagic acid, gallic acid, myricetin, and leucodelphinidin. These substances are absent from the Polycarpicae. A similar pattern of distribution is exhibited by the iridoid substances (aucubin etc.), which constitute in all probability a homologous series of plant products. Also, morphological characters are mentioned which link the Rosiflorae with the Guttiferales but remove them from the Polycarpicae. On this basis the idea is advanced that the Polycarpicae represent an odd lateral branch of the evolution of the dicotyledons which appears wholly fixed and has remained primitive in different respects, and which has only given rise to a limited number of more modern groups like Papaverales (s. str.) and Rutaceae. The Rosiflorae and the Guttiferales must have had a common origin, but one different from the Polycarpicae; it is from them that most of the choripetalous and all sympetalous groups were derived.