A New Lecanoric Acid-Producing Usnea from Mexico

Abstract

Usnea lecanorica (Ascomycotina, Usneaceae), a new species of the U. florida group from south-central Mexico, differs from all other known species of its genus by producing lecanoric acid as the major medullary constituent. The new Mexican lichen species Usnea lecanorica (Ascomycotina, Usneaceae), the subject of this report, is the first member of its genus known to produce lecanoric acid. Unlike the some 18 0-orcinol products characteristic of many scores of species in this genus, lecanoric acid is a para-depside of the orcinol series, a category previously known to be represented in Usnea by only evernic acid in U. longissima ssp. jesoensis Asah. and U. trichodea Ach. Evernic acid is the 4-O-methyl derivative of lecanoric acid; it probably also occurs in trace amounts in the new species described here. The natural but variable genus Usnea (discussion: Krog 1976) consists of about 500 species. Although thoroughly cosmopolitan, it achieves greatest species diversity in warmtemperate, subtropical and upland-tropical vegetations. The fruticose thallus with its central cord is so distinctive that the chemical data now recorded from approximately 200 species are surely correctly assigned at the generic level. Taxonomy at the species level, however, is confused because in many groups the major evolutionary modifications have been in secondary-product chemistry and amplitude of ecologic tolerance. Usnea lecanorica belongs to the U. florida complex--characteristically tufted lichens with conspicuous apotheciaconstituting in North America a series of 13 chemotypes as determined from a thin-layer chromatographic survey of 358 specimens (Fiscus 1972). No micromorphological analyses have been made, and consequently it is unknown if any of the small morphological variations seen in the U. florida complex consistently accompany major chemical discontinuities. The U. florida group in North America is characterized by certain 0-orcinol depsides (diffractaic, squamatic and thamnolic acids) and depsidones (connorstictic, constictic, 2'O-methylpsoromic (= conpsoromic), fumarprotocetraric, galbinic, norstictic, protocetraric, psoromic, salazinic and stictic acids). Additionally, some members of the U. florida group make fatty acids (including caperatic and bourgeanic acids); they all make the yellow pigment usnic acid and some produce other pigments as well. It was consequently a surprise to find two C+ red Mexican collections that produced the unsuspected orcinol depside lecanoric acid. The two small original collections were made by Robert W. Cruden in 1966 at a mountain locality some 25 km southwest of Toluca in the state of Mexico. We found four more specimens at the same locality ten years later during one of several general collecting trips for lichens of the mountain forests of south-central Mexico. Curiously, these four were the only examples of this chemotype among the many specimens of the U. florida group taken throughout the extensive regions visited. The cool, relatively moist locality near Toluca is above 3000 m elevation and is forested with Abies religiosa and Pinus sp. The new species grows upon both these trees. The most common congeneric companion 007-2745/83/254-256$0.45/0 This content downloaded from 207.46.13.163 on Fri, 08 Jul 2016 06:11:51 UTC All use subject to http://about.jstor.org/terms 1983] CULBERSON ET AL.: A NEW USNEA 255