Tasimidella, a new lichen genus from Tasmania, with a revised circumscription of the family Megalariaceae

The new crustose lichen genus Tasmidella, containing the species, T. variab ilis sp. nov. with two varieties, var. variabilis and var. inactiva var. no v., is described. Tasmidella is most closely related to Megalaria, from whi ch it differs chiefly by having simple ascospores with a layered wall. Rela tionships with superficially similar genera are discussed. A revised circum scription of the family Megalariaceae is provided to rake into account the inclusion of a second genus. (C) 1999 The British Lichen Society.