Umbilicaria decussata (Vill.) Zahlbr.
Lichen decussatus Vill., Hist. pl. Dauph. 3: 964 (1789).
Thallus 1-8 cm diam., monophyllous, rarely polyphyllous, coriaceous, rigid, orbicular, umbo peaked to elevated, coarsely granular, pruinose, wrinkled, wrinkles elevated, reticulate, decreasing in size towards margins, becoming covered with cracked granules and appearing areolate, occasionally perforate, margins entire, rounded or variously incised. Upper surface dull, pale buff to dark olive-brown or black. Lower surface sooty black with a grey to pale brown, narrow peripheral zone or occasionally blotchy, smooth, rarely obscurely vermiform, commonly bullate, umbilicus medium, compact to flat, rhizines absent. Apothecia rare, 1-3 mm diam., black, adnate, with sterile button and/or fissures, often appearing worn-gyrose, disc flat, rounded, becoming convex and distorted with age, scattered. Hymenium to 70 µm tall. Hypothecium 50 µm tall, irregular, brown. Paraphyses simple to branched, septate, 2-3 µm thick. Ascospores simple, ellipsoid colourless 6-13 × 3-6 µm.
S: Marlborough (Mt Tapuaenuku), Otago (Mt Ida, Mt Pisgah). Still very poorly known and undercollected in New Zealand. On alpine rocks.
Cosmopolitan
