Correlations and Non-Correlations of Chemical Variation Patterns with Lichen Morphology and Geography

Abstract

Recent literature on patterns of chemical variation in the lichen-forming ascomycetes is reviewed, and correlations of chemical variation patterns with respect to morphology at the generic level are presented. At the subgeneric level, reports can be grouped into: (1) examples showing distinct correlations of lichen chemistry with morphology or geography, and (2) examples showing weak correlations of lichen chemistry with morphology or geography, where chemical patterns follow morphological or geographical trends or tendencies. The recognition of chemical strains, where no correlations of chemistry with morphology or geography exist, is documented in the final section of the paper. During the 1860s William Nylander devised a simple method for identifying chemical differences between lichens by applying spot tests of potassium hydroxide or calcium hypochlorite on lichen thalli to elicit color reactions. These spot tests indicated the presence or absence of various aromatic and aliphatic substances. Today over 500 lichen sub- stances are known to be produced by the lichen- forming ascomycete fungi. Most of these substances have now been named and their structures eluci- dated (C. F. Culberson 1969, 1970; C. F. Culberson et al. 1977c). Unlike vascular plants or other groups of cryp- tograms, chemical characteristics have been em- ployed in lichen taxonomy for over 100 years. The chemical composition of most lichen species ap- pears to be uniform and constant throughout the life of the individual lichen, and the chemistry is uniform throughout the range of many species. Nor- mally one substance (atranorin, usnic acid or a xan- thone) is produced in the cortical layer of the thallus while one or more colorless substances (depsides and depsidones) are deposited on the cell walls of the medullary hyphae. Substances can be even more