The Xylariales (Sordariomycetes, Ascomycota) is an order of mostly stromatic perithecial fungi generally inhabiting wood and other plant debris, as well as some important plant pathogenic species. As a follow-up to an extensive fungal inventory conducted by D. Haelewaters and colleagues since December 2012 at the Boston Harbor Islands National Recreation Area in Massachusetts, I examined members of the Xylariales in detail, including previously unreported collections. I constructed keys for included taxa, and I provide species notes, references, substrate, and collecting data of the following Xylarialean genera: Diatrype, Eutypa, Eutypella (Diatrypaceae); Biscogniauxia, Camillea, Graphostroma (Graphostromataceae); Annulohypoxylon, Daldinia, Hypomontagnella, Hypoxylon, Jackrogersella (Hypoxylaceae); Lopadostoma (Lopadostomataceae); and Entoleuca, Kretzschmaria, Nemania, Rosellinia, Xylaria (Xylariaceae). I herein formally describe a new species, Xylaria finismundoensis sp. nov., based on combined morphology and multi-locus phylogenetic analysis. This taxon provides the first evidence of a saprotrophic lifestyle for members of the E9 phylogenetic clade of Xylaria, previously only known as endophytes.