A Contribution to the Chemistry of the Lichen Family Umbilicariaceae (Ascomycotina)

Abstract

Most species in the lichen family Umbilicariaceae accumulate the tridepside gyrophoric acid and its satellite depside lecanoric acid. For many years, the detection of chemical variation in these species was hampered by interference due to the generally high concentrations of gyrophoric acid accumulating in thalli. Recent investigations using high-performance liquid chromatography have shown that previous studies underestimated both the chemical variation and the correlations of chemistry with generic limits within the family. In the present study, an improved gradient high-performance liquid chromatographic method is combined with thin-layer chromatography to analyze representative specimens of 56 species. The known chemistry of the family is expanded, and problems in the identification of satellite compounds occurring with high concentrations of gyrophoric acid are reexamined. The Umbilicariaceae make up a distinctive and apparently isolated family of lichenized Ascomycetes. The family was early divided into as many as five genera (Llano 1950; Scholander 1934) based primarily upon apothecial morphology, but current taxonomies recognize only two, Umbilicaria and Lasallia. A recent study using enzyme electromorph data, however, found no evidence to support even that level of separation (Hageman & Fahselt 1992). Because of the distinctive morphology and generally large size of the thallus, these lichens have been favorite subjects for studies of water relations, photosynthesis, isozymes, DNA, pollution ecology, individuality, and teleomorph-anamorph relationships (e.g., Blum & Kashevarov 1986; Fahselt 1989; Hageman & Fahselt 1990, 1992; Harrisson et al. 1989; Hestmark 1991a,b; Larson 1989; Larson & Carey 1986). Additionally, some polysaccharides of the Umbilicariaceae offer potential anticancer and anti-HIV applications (Hirabayashi et al. 1989; Shibata et al. 1968a,b). The Umbilicariaceae have also been studied for their secondary products. But unlike many other lichens, in which variation in the products in highest concentration is common and for which microchemical methods have revealed useful chemical characters, most umbilicariaceous species uniformly elaborate high concentrations of the tridepside gyrophoric acid, always accompanied by smaller amounts of its probable depside precursor lecanoric acid. Most of the chemical variation in these lichens is due to the presence of low proportions of additional satellite compounds biosynthetically related to gyrophoric acid. The compounds that vary must consequently be detected and identified against a high background of gyrophoric acid, and the thinlayer chromatographic (TLC) method normally used in herbarium surveys often underestimates the chemical diversity. Even so, it was long recognized that some of the Umbilicariaceae, characterized by the production of gyrophoric and lecanoric acids, also contain an additional tridepside (umbilicaric acid), p3-orcinol depsidones, and anthraquinone pigments (e.g., Bachmann 1962; Bohman 1969; Zopf 1898). More recent surveys of Umbilicaria and Lasallia (Feige et al. 1987; Geyer 1985; Posner 1990; Posner et al. 1990, 1991, 1992) using HPLC have shown additional chemical diversity, due primarily to co-occurring O-methylated or hydroxylated gyrophoric acid derivatives (e.g., ovoic and hiascic acids). Also, the recently described tridepside crustinic acid (from U. crustulosa), which is 5-hydroxylated on the third (C) ring, is the first example of a natural product with both paraand meta-dep ide linkages (Huneck et al. 1993). The discovery of crustinic acid in 1992 by Posner and her coworkers owed much to the development f HPLC-gradient methodologies. In their surveys of Umbilicaria and Lasallia (cited above), separation and identification of lichen products relied heavily on HPLC. This method separates more lichen compounds and sees more minor products 0007-2745/96/199-211$0.00/0 This content downloaded from 157.55.39.221 on Sun, 06 Nov 2016 06:03:52 UTC All use subject to http://about.jstor.org/terms 200 THE BRYOLOGIST [VOL. 99 TABLE 1. Secondary products of specimens of Lasallia and Umbilicaria. AMT refers to the total residue from the toluene and acetone extracts; +++ = large, + = small and (+) = very small, even with a larger sample. For the proportions of the compounds, M = major, m = satellite and tr = trace compound; italics refers to compounds detected best in the toluene extract. Proportions of some compounds are variable; see text. Unless otherwise noted, all compounds were detected by TLC and by HPLC. Species AMT LEC GY UMB OVO HIAS CRU LAS NST ST SAL AT SV-1 SKY