Analysis of Phenolic Products in Lichens for Identification and Taxonomy

Abstract

The identification of secondary metabolites in lichens is a necessity for the correct determination of lichens in numerous groups, and the presence of substances is often mentioned in taxonomic keys. Numerous review papers have discussed the significance of secondary metabolites in lichen taxonomy (e.g., W Culberson 1969, 1970, 1986; WL Culberson and Culberson 1970; Hawksworth 1976; Brodo 1978, 1986; Leuckert 1985; CF Culberson 1986; Egan 1986; Rogers 1989; Lumbsch 1998a, b) and the chemistry of these substances (e.g., Asahina and Shibata 1954; Shibata 1963; Huneck 1968, 1971, 1973, 1984, 1991; Elix et al. 1984). Our knowledge of the biosynthesis of secondary metabolites in lichenized fungi has been summarised by (1969). The biological role of lichen substances was reviewed by (1986), and additional information regarding the ability of aromatic lichen substances to protect against irradiation can be found in (1995). Lichens may utilise secondary metabolites as chelating agents (Purvis et al. 1987), as inhibitors of lichenicolous fungi (Lawrey 1995), and to avoid saturation of the medulla by water (Armaleo 1993). Lists recording the distribution of secondary metabolites in different taxa have been compiled by Chicita Culberson and co-workers (CF Culberson 1969, 1970; CF Culberson et al. 1977). Some methods used in the identification of secondary metabolites in lichenized ascomycetes can be found in the literature cited below, but this chapter is restricted to examples of the two most commonly applied techniques, namely thin-layer chromatography (TLC), including high performance thin-layer chromatography (HPTLC) and high performance liquid chromatography (HPLC). Several publications deal with the identification of lichen substances, the most comprehensive being the recent book by Huneck and (1996). The reader is referred to this and the other publications for more detailed information and additional techniques used in lichen chemistry (Santesson 1973; Leuckert 1984; White and James 1985; CF Culberson and Elix 1989). Table 1 presents a list of the classes of secondary metabolites found in lichen-forming fungi.