The byssoid lichen genus, Roccellinastrum, consists of three species in Tasmania.Two of these, R. flavescens and R. lagarostrobi, are described as new. Both species grow exclusively on the leaves of Tasmanian endemic conifers and are recognized by a combination of morphological, chemical and anatomical characters. Usnic acid, found in R. flavescens, is recorded in the genus for the first time. Relationships with South American species are discussed.