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Chemosyndromic Variation in the Parmelia pulla Group

1977; American Bryological and Lichenological Society; Volume: 80; Issue: 1 Linguagem: Inglês

10.2307/3242518

1938-4378

Chicita F. Culberson, William Louis Culberson, Theodore L. Esslinger,

Bryophyte Studies and Records

Eighteen species or races of the widespread and variable Parmelia pulla group provide the second example of chemosyndromic variation in lichens, a pattern first discovered in Cetrelia. The chemistry of the P. pulla group involves biogenetically related orcinol derivatives including the new depside oxostenosporic acid, for which the structure is determined microchemically, and two other new depsides tentatively identified as the 4-O-demethyl derivatives of divaricatic and stenosporic acids. Although the total chemistry of the P. pulla group is more com- plex than that of Cetrelia, the patterns of joint occurrences of orcinol-type dep- sides are similar and in both may involve partial enzyme specificities related to hy- drophobic side chains on the phenolic secondary products. Four new species from the southern hemisphere are described: P. scabrella Essl. (South Africa), P. pictada Essl. (New Zealand), P. verrucella Essl. (South Africa, Australia, New Zealand) and P. subverrucella Essl. (Australia). Chemosyndromic variation, a new type of chemical variation in the lichen-forming fungi, was recently described in Cetrelia (Culberson & Culberson, 1976), a genus of 15 species segregated from Parmelia (Culberson & Culberson, 1968). Chemosyndromic variation in the lichens differs sharply from classical chemical variation in which con- generic chemotypes show simple replacements of one or a few substances. From the relatively large number of biogenetically related secondary compounds in Cetrelia, in- dividual species produce characteristic sets of products, or chemosyndromes, that ap- pear to show progressive chemical changes. The chemosyndromes of the 15 species of Cetrelia can be ordinated by side-chain length of substituents on phenolic acid units. Most Cetrelia species, especially those having compounds with side chains of moderate length, produce a relatively large number of substances of which one or two are in ap- preciably higher concentration than the rest. Analysis of the total chemical variation in Cetrelia suggested an explanation involving partial enzyme specificities. For example, depsidases with hydrophobic binding sites could accommodate with differing degrees of efficiency the phenolic units having different hydrophobic side chains. The chemistry