AbstractThe new genus Australidea Kantvilas, Wedin & M. Svensson is described to accommodate Lecidea canorufescens Kremp., a widespread lichen in temperate Australasia. It is characterized by a crustose thallus with a green photobiont, reddish brown, biatorine apothecia with an internally hyaline, cupulate proper exciple constructed of branched and anastomosing hyphae, mainly simple paraphyses, 8-spored, Porpidia-type asci and simple, hyaline, non-halonate ascospores. A phylogenetic analysis places the new genus in the family Malmideaceae. Lecidea canorufescens Kremp., L. glandulosa C. Knight, L. immarginata R. Br. ex Cromb. and L. intervertens Nyl. are lectotypified. These names, plus L. dacrydii Müll. Arg. and L. eucheila Zahlbr., are all synonyms of Australidea canorufescens (Kremp.) Kantvilas, Wedin & M. Svensson comb. nov. Several genera superficially similar to Australidea, including Malcolmiella Vĕzda, Malmidea Kalb et al. and Myochroidea Printzen et al., are compared. A comprehensive anatomical and morphological description of the genus Malcolmiella, recorded for Tasmania for the first time, is also provided. The new combination M. interversa (Nyl.) Kantvilas, Wedin & M. Svensson is introduced and the names M. cinereovirens Vĕzda and M. cinereovirens var. isidiata Vĕzda are reduced to synonyms. The systematic position of this genus remains unclear, although phylogenetic analysis suggests its affinities lie with a group of genera that includes Bryobilimbia Fryday et al., Romjularia Timdal and Clauzadea Hafellner & Bellem.