Flora of New Zealand Series

Thallus crustose, areolate-rimose, leprose-verruculose to ± effuse, rosette-forming to irregularly spreading, with or without a delimiting marginal prothallus. Photobiont green, Trebouxia. Apothecia lecideine, often with a spurious thalline margin, disc innate, punctiform or flattened to subglobose, dark brown or black with or without a grey-white pruina. Asci elliptical-oblong or clavate, 8-spored. Paraphyses capillary, subclavate at apices. Ascospores brown, ovoid-oblong to ± fabiform, thick-walled and usually 3-septate, rarely submuriform.

Diplotomma comprises c. 35 species and is included in the family Physciaceae. It is distinguished from Buellia and from Diploicia in the characteristic 3-septate to submuriform spores. One species is known from New Zealand, from limestone rocks where it forms distinctive white patches often of very great size.