Since 1886 twenty-six taxa of Fossombronia Raddi have been reported from northern and eastern Asia, Oceania, the Malay Archipelago, and New Zealand. Of these, sixteen were named as new taxa. Although several regional studies have been published, no detailed systematic study of these taxa has ever been undertaken. I have conducted a comprehensive study of the gametophyte and sporophyte characters of all the taxa reported from the region to determine the true diversity of the genus in the study area. My study of type specimens was complemented with extensive collections of Fossombronia from the major herbarium of the region. This study showed that gametophyte characters, such as, oil body and pseudoperianth morphology, gametangia arrangement, thallus branching habit, and thallus color are systematically important characters that were ignored by earlier workers. Examining all characters of both generations, I conclude that there are only twelve taxa represented in the study area. Of these taxa, species such as F. cristula Austin, F. foveolata Lindb., F. pusilla L., F. wondraczekii (Corda) Dumort. ex Lindb., and F.loitesbergii Shiffn. have a wide distribution, being reported from several continents throughout the world. In contrast, the remaining seven species, F. microspora Herzog, F.reticulata Steph., F. kashyapii Srivastava et Udar, F. intestinalis Taylor, F.papillata Steph., and two species new to science, have very narrow distributions, being reported from but one or two continents.

Key words: Asia, Fossombronia, Malay Archipelago, New Zealand, Oceania, revision