Abstract
Marasmiellus (Omphalotaceae, Agaricales) specimens collected in Thailand were investigated based on morphological characteristics and molecular phylogenetic analyses. In the present study, two species are introduced as new to science, namely Marasmiellusthailandicus and M.minutisporus. Phylogenetic analyses were carried out based on the internal transcribed spacer (nrITS) and nuclear ribosomal RNA large subunit (nrLSU) regions, and the results revealed that the two new taxa are distinct species within Marasmiellus. Another specimen was identified as M.scandens and is reported for the first time with morphology and molecular data from Thailand. Descriptions, illustrations, and phylogenetic results are provided. In addition, M.diaphanus and M.colocasiae are proposed as new combinations of Collybiopsisdiaphana and Paramarasmiuscolocasiae, respectively, based on the phylogenetic evidence.