Abstract
Hymenopellis is the most diverse genus in the group of oudemansielloid/xeruloid taxa (Physalacriaceae). This genus has a worldwide distribution with records mostly from Europe and America. Asian taxa are least represented. In this paper on Hymenopellis from Thailand, two novel species are introduced, and a Hymenopellis collection affine to H.orientalis is described. Macro and micromorphological characters are described. Maximum likelihood and Bayesian phylogenetic analyses were performed on combined ITS and nrLSU regions to confirm taxonomical placement and infer the phylogenetic affinities of the studied species. Hymenopellisstraminea sp. nov. is straw-yellow, with medium-sized basidiomata, abundant and diverse in form cheilocystidia, few, narrowly lageniform to fusiform pleurocystidia, and clamp connections at the lower part of the stipe. Hymenopellisutriformis sp. nov. has mostly utriform pleurocystidia and 2-spored basidia. In the inferred phylogenies, the new species from this study formed distinct clades well supported by bootstrap proportions and posterior probabilities. The studied specimen affine to H.orientalis produced 2-spored basidia whereas published descriptions of other specimens mention 4-spored basidia. Moreover, the genetic distance between ITS sequences of this specimen and that of a Hymenopellisorientalis specimen from GenBank was 1.30-2.57%. Therefore, the conspecificity of our specimen with H.orientalis is uncertain, and additional specimens are needed to fully confirm its identity.