The genus Marchantiana has been a victim of changeable concepts, partly due to erroneous DNA sequences published with its description. Based on new molecular sequencing, new chemical analyses and additional field work, mainly in Patagonia, Tasmania and New Zealand, we present a new taxonomic classification for the genus and related species. M. michelagoensis is confirmed to belong to Marchantiana, and the genus Streimanniella, for which this species was the generic type, is synonymized with Marchantiana. We combine Caloplaca haematommona, C. magnetensis, C. tomnashii and C. phaeocincta into Marchantiana as M. haematommona, M. magnetensis, M. tomnashii and M. phaeocincta, respectively. A new genus Taedigera is described to cater for three previous Marchantiana species and one Caloplaca species, with the new names T. pyramus, T. ramulicola, T. subpyracea and T. epibrya, respectively. Two species, T. flammea and T. gallowayi, both twig epiphytes from New Zealand, and one species, M. tasmanica, from Tasmania, aredescribed as new to science based on molecular and secondary chemical characters. Marchantiana burneyensis, M. kalbiorum and M. seppeltii are excluded from the genus Marchantiana based on newly generated sequences of type material. A key is provided to the species groups in Patagonia, Tasmania and New Zealand.