The lichen genus Calycidium Stirt. (Calycidiaceae, Lecanorales, ‘Caliciales’ s. lat.) contains two species: C. cuneatum Stirt., distributed in Australia (Tasmania) and New Zealand, and C. polycarpum (Colenso) Wedin, comb, nov., distributed in Argentina, Australia (Tasmania), Chile and New Zealand. The morphology, chemistry, ecology and distribution of the two species is discussed, as is the taxonomic position of the genus. Calycidium is reported as new to Argentina.