EVOLUTIONARY SIGNIFICANCE OF XANTHONES IN GENTIANACEAE - A REAPPRAISAL

Three evolutionary assumptions for xanthone substitution patterns were analysed in 12 genera of Gentianaceae, computing cladograms based on chemical and morphological characters. Two types of specialization trends seem to prevail: one biosynthetic with oxidative steps in xanthone ring A and with reduction in ring B and another one with decreasing diversity of xanthone compounds, caused by evolutionary loss. Therefore hexaoxygenation (1,3-dioxygenation of ring A and tetraoxygenation of ring B) as well as co-occurrence of tri-, tetra-, penta- and hexasubstituted compounds are probably primitive characters in the family This explanation will result in three main evolutionary lines of analysed taxa: subtribe Erythraeinae having the most primitive, the Swertia-line an intermediate and the Gentiana-line an advanced position. These constellations are in congruence with the constructed morphological cladograms.