A Phylogenetic View of Chemical Evolution in the Lichens

Abstract

The distribution of 209 chemical substances among the 2,315 species of lichens that have been reported in a literature of approximately 1,000 papers is summarized. The information is used to assess the extent and the nature of chemical evolution in the lichen-forming fungi and to evaluate the present supraspecific (especially generic and familial) classifications of these plants. The order Lecanorales is the seat of most of the chemical variation, especially in the secondary natural products most useful in systematics, namely the sub- stances formed by coupling of phenolic units such as the orcinol and p-orcinol compounds. Most genera and families that are well defined morphologically and appear to represent natural taxa show highly uniform chemistries of several to many biogenetically related substances or sets of substances. Many genera with chemistries discordant for the families in which they are currently classified also seem to have affinities elsewhere from morphological information. In the lichen-forming fungi, which lack a fossil record, comparative phytochemistry is the most useful independent check that exists to evaluate the naturalness of systems of classification based upon morphology.