Differences in secondary metabolites produced by lichens are not always genetically based, and even if genetically based may represent only a one gene difference. Taxonomic decision involving secondary metabolism should be based on the degree of difference demonstrated between biosynthetic pathways, not on the individual products. No taxonomic status should be accorded to entities which differ only in products from a single biosynthetic pathway, but varietal status should be given to those which have different biosynthetic pathways. Species status is justified if chemistry is correlated with morphological or proven physiological difference, or if more than one major biosynthetic system is involved. While ecological and biogeographic differences point to the likelihood of differences being found, if no differences can be demonstrated which in themselves justify taxonomic separation, then features ought not be allowed to influence the taxonomic decision.
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