Interpreting Chemical Variation in Lichens for Systematic Purposes

Although the usefulness of chemistry in the taxonomy of lichen fungi is unquestioned, its application to specific systematic problems varies considerably. The reasons for this inconsistency and for the reluctance of some workers to use chemical characters with confidence, involve 1) practical problems (e.g., difficulty in demonstrating certain compounds), 2) biological factors (e.g., chemical variation due to the nature of the lichen), and 3) philosophical differences (e.g., having to do with various species concepts and character weighting). These problems are not insurmountable. With a better understanding of the nature of the problems, lichen taxonomists should be able to reduce the number of inconsistencies in the use of chemical data.