Lepraric acid derivatives as chemotaxonomic markers in Hypoxylon aeruginosum, Chlorostroma subcubisporum and C. cyaninum, sp. nov.

Hypoxylon aeruginosum (Xylariaceae), an infrequently encountered predominantly tropical pyrenomycete, of which two varieties are known to science, is characterised by having a cyan blue stromatal surface or subsurface. In the course of our ongoing chemotaxonomic evaluation of the Xylariaceae, specific profiles of H. aeruginosum were observed by high performance liquid chromatography, coupled with diode array detection and mass spectrometry (hplc-DAD/MS). By comparison with an authentic standard, lepraric acid and several yet unidentified metabolites with similar hplc-DAD/MS characteristics were detected in the stromata of the type material and other specimens of this species. Interestingly, lepraric acid was hitherto only known from lichenised ascomycetes. Hypoxylon aeruginosum, which is here reported first from Africa and Asia, contained none of the metabolites that were previously detected in other Xylariaceae, except for stromata growing hyperparasitically on other Hypoxylon species. A different lepraric acid derivative was also detected in the type specimen of Chlorostroma subcubisporum, which differs from H. aeruginosum by having a green stromatal surface, cuboid ascospores, and in lacking an amyloid ascal apical apparatus. A second species of Chlorostroma, which showed essentially the same metabolite profile as H. aeruginosum, is described from Thailand. We conclude that Chlorostroma and H. aeruginosum are closely related. However, no taxonomic conclusions are drawn from these findings because no cultures have so far become available to study their anamorphic morphology, their secondary metabolites in culture, and their molecular phylogeny. Taxonomic novelty: Chlorostroma cyaninum Læssøe, Srikitikulchai & J. Fournier, sp. nov.