Herpothallon biacidum, a new lichen species from tropical Australia

Herpothallon biacidum Frisch et al. is described from Queensland, tropical Australia. The new species is characterized by a thick byssoid thallus that is loosely attached to the substratum, globular to claviform to short cylindrical pseudoisidia, a brown to brownish black hypothallus, and by the presence of gyrophoric and norstictic acids. This is the first reported co-occurrence of gyrophoric and norstictic acids in the genus. The differences between H. biacidum and other species containing either norstictic acid or gyrophoric acid are discussed. Herpothallon biacidum is also compared with Cryptothecia eungellaeae. Both occur in north Queensland and have the same chemistry, but the latter has a closely adnate thallus and lacks the dark hypothallus and pseudoisidia. The circumscription of Herpothallon and its distinction from Cryptothecia are discussed.