The epiphytic species, Megaloblastenia sorediata Kantvilas sp. nov., is described from the wet forests of Tasmania and New South Wales; its preferred host is the understorey tree Pomaderris apetala. The newly described species is distinguished from the widespread M. marginiflexa (Hook.f. & Taylor) Sipman chiefly on the basis of having soredia, although its apothecia, asci and ascospores are also marginally smaller. A key to the three species of Megaloblastenia is presented, and the application of soredia as a taxonomic character is discussed briefly. Keywords: Australia, lichens, species pairs, Tasmania, taxonomy.