Taxonomic revision and phylogenetic analysis of Xylaria in French Guiana, including 38 new species and one new combination.

BACKGROUND: French Guiana is one of the earliest regions in the Neotropics where Xylaria species were extensively explored, notably by François Mathias René Leprieur during the 1830s, with many taxa subsequently described as new by Jean Pierre François Camille Montagne. Despite this long history and its clear biogeographical importance, the Xylaria diversity of French Guiana has remained insufficiently documented. Numerous species have been poorly defined, misidentified, or lack molecular data, and no modern, integrative synthesis combining morphology, typification, and phylogenetics has been available for the region. RESULTS: Based on extensive recent field collections by two of us (JF and CL) and a re-examination of historical material, a total of 98 taxa of Xylaria are documented from French Guiana, with X. cantareirensis and X. guadalupensis additionally treated from Brazil and the French West Indies, respectively. Among these, 39 taxa are considered novel to science, including 38 newly described species and one newly recombined name. Multilocus phylogenetic analyses based on protein-coding loci support the separation of the analyzed taxa and clarify relationships among morphologically similar taxa. Of the newly described species, 37 were included in the phylogenetic analyses and are further confirmed as distinct. Several species closely related to X. scruposa are shown to constitute a species complex. Numerous historical names originally reported from French Guiana are re-evaluated through type studies, epitypifications, and critical morphological reassessments. These results highlight the remarkable Xylaria species richness of the region. CONCLUSION: This study demonstrates that French Guiana harbors a remarkably rich and complex Xylaria diversity that remains only partially resolved. The integration of detailed morphology and molecular phylogenetics reveals a much higher level of diversity than previously recognized and exposes significant taxonomic uncertainty in several species complexes. These findings underscore the need for continued sampling, especially of fresh material suitable for culturing, sequencing, and emphasize the importance of French Guiana as a key region for understanding the taxonomy, evolution, and biogeography of Xylaria in the Neotropics.