Investigations into the bryophyte flora of Madagascar as part of the MadBryo project, show that five moss genera (Actinodontium Schwägr., Aulacopilum Wilson, Forsstroemia Lindb., Haplohymenium Dozy & Molk., and Herzogiella Broth.) are new for the island. For three additional taxa we clarify the correct name to use for Malagasy specimens. Ectropothecium perrieri Thér. is placed in synonymy with Herzogiella cylindricarpa (Cardot) Z.Iwats. and Lepidopilum diversifolium Renauld & Cardot is reduced to a synonym of Thamniopsis utacamundiana (Mont.) W.R.Buck. These particular cases highlight the hidden diversity lurking within underutilized natural history collections. They should also serve as a reminder that older collections need to be critically reexamined as our taxonomic concepts evolve.