Fluorescence of Lichen Depsides and Depsidones as a Taxonomic CriterionAuthor(s): Mason E. Hale, Jr.Source: Castanea, Vol. 21, No. 1 (Mar., 1956), pp. 30-32Published by: Southern Appalachian Botanical SocietyStable URL: http://www.jstor.org/stable/4031709 .

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Fluorescence of Lichen Depsides and Depsidones as a Taxonomic Criteriont

MASON E. HALE, JR.

Biochemistry is being enlisted frequently as a taxonomic criterion in the study of lichens. It is now common practice to apply reagents like potassium hydroxide or p-phenylenediame to the lichen thallus to elicit color tests or even to identify the individual chemical components microchemically. Another technique, fluorescence analysis, was recent- ly employed by two taxonomists (Chernohorsky, 1950; Ozenda, 1951) as an aid in species identification. Although certain species fluoresced in ultraviolet radiation, the investigators made no effort to establish the cause of this phenomenon. A study of the fluorescent properties of the common depsides and depsidones extracted from lichens was undertaken by the present writer in order to delimit this property for taxonomic purposes.

The lichen substances were identified by the microchemical crystal methods of Asahina (cf. Asahina, 1954) and by partition chromatog- raphy (Wachtmeister, 1955). Purified samples as well as dried lichen specimens of proven chemical constitution were exposed at 20 cm. from a two tube laboratory UV lamp with Wood filters, trans'mitting maximum radiation at 3600 A with a range of 3200-4000 A.

Results and Discussion Nine purified substances exhibited intense fluorescence which was

plainly visible even in the thalli of lichens which contained them. These are listed in Table I. Wavelength of emitted radiation was

TABLE I. Fluorescent lichen depsides and depsidones (*) with color emitted and the chief soturce of the compound. The substances are listed in order of decreasing intensity.

Acid Color emitted Source *Alectoronic aci(l bluish-white Cetraria richardsonii Squamatic acid white Cladonia squamosa Sphaerophorin white Sphaerophorus spp.

*Lobaric acid greenish-white Stereocaulon spp. Divaricatic acid white 4nzia colpodes Evernic acid white Evernia nzesornorpha

*Psoromic acid greenish-white Rhizocarpon geographictim Perlatolic acid white Cladonia decorticata Barbatic acid greenish-white Cladonia robbinsii

measured for a few compounds available in quantities sufficient for analysis on a Bunsen-Kirchhoff spectroscope: alectoronic acid, 4800- 5000 A; lobaric acid, 5100-5400; and evernic acid, 5500-6200. The spectrum appeared as a very diffuse white band.

Another series of six compounds fluoresced weakly in the pure state and in the lichen thalli at not more than 20 cm. from the lamp.

iContribution No. 75 from the Herbarium of West Virginia University. Sup- ported in part by a grant from the Research Fund, University of Wichita, Kansas.

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These include lecanoric, olivetoric, baeomycic, norstictic, obtusatic, and physodic acids, which emit white to pale orange-white light.

A final group of depsides and depsidones did not fluoresce signifi- cantly under the experimental conditions: atronorine, chloratronorine, diploicin, and pannarin, and a-collatolic, diploschistesic, fumarproce- traric, gyrophoric, homosekikaic, physodalic, protocetraric, salacinic, stictic, thamnolic, and variolaric acids.

There is a definite correlation between intensity of fluorescence and substituents on the acidic phenyl ring. All six intensely fluorescent depsides have a 2-hydroxy, 4-methoxy configuration. The methoxyl radical confers strong fluorochromic properties on the depside nucleus, because 4-hydroxy homologues are only weakly fluorescent, as in the case of evernic acid (4-methoxy lecanoric acid) and lecanoric acid. This observation is in agreement with Wachmeister's results (1952) where 4-methoxy derivatives of depsides are reported to be more intensely fluorescent than the 4-hydroxy derivatives. Among the depsidones there are no comparable correlations between fluorescence and chemical structure.

In conclusion, white light fluorescence in lichens can apparently be traced to the presence of certain depsides and depsidones, and it is possible therefore to predict this property for any lichen of known chemical constitution. Unfortunately at least nine widely distributed substances emit indistinguishable white light, and the ultraviolet lamp cannot help a taxonomist separate them. In addition, intensity of fluorescence varies from zero to very intense so that it may often be difficult to decide whether a lichen thallus is definitely fluorescent or not in the absence of a standard light source for comparison.

Fluorescence analysis still has some restricted use in taxonomic problems where the components of a few lichen species under study are well known, one being fluorescent, the other not. For example there are several yellow Parmneliae which are very similar in external appearance. One group (P. centrifuga, P. separata) contains the fluorescent depsidone alectoronic acid, while the other group (P. con- spersa-stenop hyllha) contains negatively fluorescent betaorcinol depsid- ones. Individual specimens can be quickly sorted into two groups without further complicated microchemical tests by simply exposing them under an ultraviolet lamp. Similar examples may be found in Stereocaulon and Cetraria. As a rule, however, microchemical crystal study and chromatography offer the only precise means to the taxon- omist for identifying the lichen substances.

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LITERATURE CITED

As;ahina, Y. 1954. Chemis,try of lichen substances. Tokyo. Chernohorsky, Z. 19150. Fluorescence of lichens in ultra-violet light. The genus

Parmelia. Stud. Bot. Cechoslovaca 11: 1-3. Ozenda, P. 1951. Fluorescence des lichens en lumiere de Wood. Compt. Rend.

233: 194-195. Wachtmeister, C.. A. 1952. Studies on the chemistry of lichens. I. Separation of

depside coimponents by paper chromatography. Acta Chim. Scand. 6: 818-825. 1955. Flechtensaure, in Linskens, H. F., Papier-chromatographie in der

Botanik. pp. 99-104. Berlin.

DEPARTMENT OF BIOLOGY

WEST VIRGINIA UNIVERSITY, MORGANTOWN

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