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Lecidea umbonata (Hepp) Mudd
Family: Lecideaceae
[Biatora umbonata Hepp,  more]
Lecidea umbonata image
Thompson, J., 1997. American Arctic Lichens: The Microlichens.
Thallus chalky white, frequently zonate with black hypothallus lines, continuous or weakly chinky. Apothecia immersed to adnate, to 2.4 mm broad; margin well developed; exciple with green or black-green outer layer, interior pale; disk flat, velvety black, frequently with central umbo of sterile tissue; hypothecium hyaline to brownish ocher; epithecium green to brown; hymenium 50-80 μm, hyaline to roseate, rarely pale greenish; subhymenium coppery green; paraphyses very gelatinous, simple or occasionally branching and anastomosing, 1.8-2.2 μm, tips capitate to 4.5 μm; asci clavate; spores blunt ellipsoid, without halo, with conspicuous plasma bridge and appearing 2-celled, 8-15 x 5-8 μm.

Reactions: medulla K—, C —, KC —, P-, I—to strongly 1+ blue; outer exciple and epihymenium HN03+ purple.

This species grows on calcareous rocks and pebbles. It is circumpolar arctic-alpine, in North America ranging south to Colorado and Utah.