THE USE OF CHEMISTRY IN THE SYSTEMATICS OF THE LICHENS

Abstract

SummaryThe extracellular metabolic end‐products that accumulate on the outer surface of the cell walls of the fungal hyphae in lichens have long been used in taxonomy. Although most morphological species of lichens are chemically uniform with regard to these substances, many others are differentiated into chemical races having distinct geographic distributions. The commonest type of chemical variation, noted in hundreds of examples, is a replacement series of the main constituent substances of the medulla. The fact that major chemical races in apparently sexually reproducing, morphologically uniform or nearly uniform lichens maintain their complete identity in places where they are sympatric suggests that such races are perhaps better regarded as distinct species. Such interpretation is further supported by the recent demonstration that where six such races are sympatric in an environmentally telescoped maritime community in Britain, the chemically different plants select different habitats, resulting in conspicuous zonation but with no alteration of plant characteristics where zones overlap. Examples of the use of lichen chemistry in genus‐level taxonomy are also given.