Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

Thallus: continuous to dispersed/scattered, effuse, composed of isidiate to minutely coralloid-elongated granules granules: 25-150(-200) µm tall, 25-50 µm in diam. surface: brown (blackish or red-brown) Apothecia: usually scattered when present, rarely crowded and confluent, 0.2-0.6 mm in diam. exciple: paler than disc (sometimes darkened in Sonoran specimens) epihymenium: brown hymenium: pale brown, 60-85 µm tall, I+ reddish orange hypothecium: pale brown, K- asci: cylindrical-clavate, 8-spored ascospores: hyaline, simple (to 1-septate), ellipsoid, 8-12 x 4-5 µm Spot tests: thallus (squash) K-, C+ pink/red, KC+ red, P- Secondary metabolites: thallus with gyrophoric acid, +lecanoric acid, +5-O-methylhiascic acids. Substrate and ecology: in a wide range of acidic habitats, occurring on dead bark and wood of fallen trees and stumps, rotting fence-posts, plant debris, tree roots, +horizontal branches, shaded siliceous rocks and humus-rich soils, also a primary colonizer of burned areas World distribution: North America, Europe and Australia Sonoran distribution: Arizona and Chihuahua. Notes: Placynthiella icmalea is easily noticed when growing as a wide-spreading, brown, isidiate crust, but often also occurs in small patches as a less conspicuous, scattered, sterile crust of coralloid granules among other lichens, including other species of Placynthiella. It is easily distinguished from other Sonoran species by the C+ pink reaction of the thallus and by the apothecia, that have margins paler than the disc.