A Survey of the Chemistry of the Usnea florida Group in North America

Abstract

The Usnea florida group was studied by thin-layer chromatography to elucidate the range of natural-product variation, primarily in North American representations. Sixteen chemical constituents in 13 different combinations were identified in the 358 specimens examined. Most of the specimens produced p-orcinol depsidones, salazinic and norstictic acids being the most common of these. But p-orcinol depsides and one orcinol depside, lecanoric acid, were also found. The latter substance is reported for the genus Usnea for the first time. The genus Usnea has long posed a problem to students of lichenology because in many primarily asexual groups a seemingly continuous array of morphological forms has precluded the recognition of well-defined species. Other groups, especially some sexually-reproducing ones, are less variable morphologically, but even most of these are poorly understood systematically. The individuals of the almost consistently fertile Usnea florida complex offer an example of the latter situation. The only intensive American studies on this group were made by Hale (1962) and Moore (1968), and these concerned only the representation in the eastern United States. The aim of the present study is to elucidate the patterns of chemical variation in the U. florida group in North America in the hope of contributing to a future taxonomy. Obviously, no general systematic treatment can emerge without analysis of the subtle morphological variation here. The value of chemical variations as markers of dis- continuities is now so well appreciated in lichenology, however, that the probability is high that a knowledge of thallus chemistry will be an indispensable guide to future studies of nonchemical variation.