Distribution and evolution of secondary metabolites in Eriocaulaceae, Lythraceae and Velloziaceae from "campus rupestres"

Abstract

Hypotheses are presented on the evolution of structural patterns of secondary metabolites (flavonoids and foliar wax alkanes) and fatty acids of families of "campos rupestres". The distribution of fatty acids is given for genera of Lythraceae, with emphasis on Cuphea (supposedly more advanced) and Diplusodon. Compounds with saturated short chains represent a derived condition in Lythraceae although they are probably restricted to Cuphea. It is suggested that evolution selected for more complex flavonoid patterns in Cuphea, with the inclusion of C-glycoflavones and methoxylated flavonols (rhamnetin and isorhamnetin), which are not found in members of Diplusodon and Lafoensia. The supposedly primitive groups of Eriocaulaceae (e.g., Paepalanthus) presented more complex flavonoid patterns characterized by flavones and flavonols, the latter frequently being 6-hydroxylated or methoxylated. More advanced groups of Eriocaulaceae (e.g., Leiothrix and Syngonanthus) apparently possess only flavones, C-glycoflavones are a salient feature of species with smaller habits. In Velloziaceae, members of the primitive subfamily Vellozioideae show distribution of alkanes of foliar epicuticular wax in which C27, C29 or C31 predominate; members of the derived subfamily Barbacenioideae usually show distributions with a predominance of C33 or C35, while species of Pleurostima (Barbacenioideae) have C31 as the main homologue, thus being intermediate between the two subfamilies. It is suggested that the evolution of alkanes in Velloziaceae follows a trend toward elongation of carbon chains. The condition of advanced or primitive chemical patterns is inferred from the results of cladistic analyses based on morphological characters (Eriocaulaceae and Lythraceae), and morphological and molecular characters (Velloziaceae).