The taxonomy of three recently collected species of peat mosses (Sphagnales) from Île Amsterdam, Terres Australes et Antarctiques Françaises, is reviewed. Two species belong to Sphagnum subgenus Subsecunda, while a third has uncertain taxonomic affinity. One of the Subsecunda species has previously been described under the name S. islei Warnst. based on material from Île Amsterdam and we provide an amended description. A second species is described as S. complanatum sp. nov. Both species share morphological characteristics with S. capense Hornsch., known from Southern Africa, Malawi, Madagascar, and Reunion. The third species is distinguished by several morphological characteristics and is described as S. cavernulosum sp. nov. It has morphological characteristics that are shared with the subgenera Sphagnum and Acutifolia, and also subgenus Subsecunda. Among known Sphagnum species, the closest morphological relative seems to be S. novo-caledoniae Paris & Warnst., described from southern Melanesia in Oceania. The morphology of these three species is described. At present, these three species appear to be endemic to Île Amsterdam. Their phylogenetic affinities and likely evolutionary histories are discussed based on their morphological characteristics. Molecular data are necessary for further evaluation of their phylogeny, taxonomic relationships, and phylogeography, but repeated attempts to obtain gene sequences have so far failed.