Flora of New Zealand Series

Thallus squamulose or small-foliose, orbicular to spreading, with a ± prominent, marginal black prothallus of felted, black hyphae. Photobiont green, Protococcus. Cephalodia small, grey-blue, squamulose to subplacodioid, containing a blue-green alga (? Nostoc). Apothecia biatorine, with a pale proper margin, soon disappearing. Ascospores 8 per ascus, biseriate, simple, colourless, ellipsoid or elongate-ellipsoid, walls smooth or warted.

Psoromidium is a Southern Hemisphere genus of 2 species included in the family Pannariaceae occupying a position intermediate between Psoroma and Parmeliella. It is most closely related to Psoroma in having a green photobiont, and superficial laminal cephalodia, but the structure of the apothecia also ally it with Parmeliella. Two species (as Psoromaria Nyl.) are discussed in detail by Lamb [ Lilloa 26: 408-411 (1953)]. Two species are known from New Zealand.