A comparison between chemical and molecular characters for the determination of phylogenetic relationships among plant families: An appreciation of Hegnauer's "Chemotaxonomie der Pflanzen"

The views on the natural relationships among plant families belonging to the Asteridae s.l. on the basis of chemical profiles expressed in Hegnauer's series "Chemotaxonomie der Pflanzen" (1962-present) are compared with the results of cladistic analyses of the rbcL gene DNA sequences in those families. The suggestion, based on chemistry, that the Cornaceae are not closely related to the Apiaceae and Araliaceae, is supported by molecular evidence, and so is the view that the Apiaceae and Araliaceae are closer to the Asteraceae instead. Likewise a close affinity between the Scrophulariaceae and Lamiaceae on the one hand, and between the Solanaceae and Boraginaceae on the other is confirmed, instead of close connections between the Scrophulariaceae and Solanaceae, and between the Lamiaceae and Boraginaceae, which has often been the traditional view. Two small families of water plants with reduced flowers, the Callitrichaceae and Hippuridaceae, which used to be placed in widely different orders by different systematists, show chemical profiles which indicate close relationships to the scrophulariaceae and Lamiaceae. Again molecular data are congruent with the chemical ones. In turn, unexpected molecular results have been supported by chemical evidence, e.g. the placement of the Polemoniaceae close to the Primulaceae and Theaceae, and that of Eucommia next to Aucuba. However, the chemistry of the Menyanthaceae does nor unequivocally support the repositioning of this family from the Gentianales to the affinity of the Asteraceae suggested by molecular data. On the whole, molecular trees based on rbcL DNA sequences appear to provide a very useful framework to assess the comparative merits and usefulness of secondary compound classes as chemotaxonomic characters, and molecular information also can be used as a tool to study the evolution of small chemical compounds. On the other hand, chemical characters can be used as an additional support for DNA trees. (C) 1999 Elsevier Science Ltd. All rights reserved.