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Marasmius is a widely represented genus in tropical areas, particularly in the Neotropics, which holds exceptional diversity. Previous studies have shown that traditional sections of the genus (e.g. sensu Singer) are still in conflict with phylogenetic data. This paper addresses some issues concerning morphology at the sectional level, section Neosessiles in particular, with regards to taxonomic concepts and partial phylogenetic relationships of new Neotropical species with interesting combinations of inter-sectional characteristics. Taxa descriptions in this study include Marasmius conchiformis sp. nov., M. conchiformis var. dispar var. nov., M. conchiformis var. lenipileatus var. nov., M. griseoroseus, M. griseoroseus var. diminutus var. nov., M. linderoides sp. nov., and M. longisetosus sp. nov. Some of these taxa have pleurotoid habit, and because this condition is poorly known in Marasmius, we considered it appropriate to look at their phylogenetic placement with respect to other species of the genus. We conducted Bayesian and Maximum Likelihood analyses on ribosomal 28S long subunit (LSU) and internal transcribed spacer (ITS) alignments to verify the singularity of the new taxa and to make an assessment of their relationships, regarding morphology, to other species of Marasmius. Overall, molecular and morphological data do support three new distinctive species and three varieties. Part of our findings also supports the view of some macromorphological and micromorphological characters as being highly homoplasic. [ABSTRACT FROM AUTHOR]