Marasmius mbalmayoensis (Basidiomycotina, Marasmiaceae) growing on decayed leaves of Canarium schweinfurthii in the Mbalmayo Forest Reserve, Cameroon, is described. The species is remarkable due to the large basidiomata with shallow orange yellow umbilicus, long central stipe accompanied by similar long rhizomorphs on thickened basal mycelium and large lacrymiform to sigmoid basidiospores. The coarsely plicate pilei with lilac, violet to dark violaceous tints, and large distant adnate lamellae are reminiscent macroscopically of the tropical African species M. bekolacongoli. The phylogenetic relationship among M. mbalmayoensis and M. bekolacongoli was assessed, extended to other species of sects. Globulares and Sicci based on DNA sequences. Phylogenetic analysis based on nuc-LSU rDNA sequence data of selected Marasmiaceae taxa confirmed the placement of M. mbalmayoensis within the Marasmius spp. and its phylogenetic separation from M. bekolacongoli. Amyloflagellula inflata, which a BLAST analysis closely related to M. mbalmayoensis, clustered in the same clade with M. mbalmayoensis and M. bekolacongoli. The findings also indicated the complexity of M. bekolacongoli.