Par Fournier J., Lechat C.
Vol. 7 (2) – 02 avril 2015
Résumé (anglais) : In June 2012, a field trip carried out over two weeks in two different localities in French Guiana resulted in a collection of 256 specimens of pyrenomycetes, mostly Xylariaceae. Out of them 42 specimens of Hypoxylon were recorded, several of them could not be equated to known species. Specimens of Hypoxylon collected by C. Lechat during previous collecting trips in French Guiana in 2008 and 2010 are likewise included in this survey. As a result of the thorough morphological study of these specimens 13 taxa are presented herein, including six new species, H. aureolimbatum, H. leprieurianum, H. nudum, H. paracouense, H. rhombisporum and H. verruciperisporium that are described, illustrated and commented upon. H. aureolimbatum strikingly resembles the temperate species H. subticinense but besides its different geographical distribution it deviates in the combination of morphological differences of stromata, asci, ascospores and asexual morph associated on natural substrate; H. leprieurianum is segregated from Hypoxylon spp. with similar external morphology based on small equilateral ascospores with broadly rounded ends, a perispore indehiscent in KOH and a faint short germ slit; H. nudum is unique in having a stroma reduced to a black basal tissue and lacking stromatal pigments; Hypoxylon paracouense resembles H. duranii but deviates by different KOH-extractable pigments and smaller ascospores with a sigmoid germ slit; H. rhombisporum is diagnosed based on frequently rhomboid ascospores with laterally ridged epispore and several further morphological differences from the closely related H. rectangulosporum; H. verruciperisporium is unique in having a verrucose perispore. Four rarely recorded species are likewise described and illustrated: H. aeruginosum, H. musceum and H. trugodes that are recorded from French Guiana for the first time, and H. fusoideosporum that was only known from two collections in French Guiana and Guyana. Finally, two collection deviating respectively from H. cinnabarinum and H. hypomiltum and possibly different are described, for which no formal taxonomic decision can be made until the natural range of variations encountered in these taxa is clearly understood; furthermore, three specimens are tentatively referred to H. dieckmannii, a pantropical taxon that appears to be a complex of closely related species. The holotypes of H. duranii, H. musceum and H. rectangulosporum that were studied for comparison are likewise illustrated. A dichotomous key the Hypoxylon spp. known from French Guiana is provided. In conclusion, the use of new morphological characters to segregate Hypoxylon spp. is suggested and commented