Bottlebrush Frost Lichen

Appearance

Thallus: foliose, up to 7 (rarely 8 or 9) cm in diam., irregular to more often orbicular lobes: linear-elongate and discrete to somewhat irregularly rounded and partly imbricate, 1-2 (-3) mm broad, usually ± flat to irregularly concave, prostrate upper surface: gray to mostly gray-brown or brown, with a partial (lobe ends) or occasionally almost completely pruinose, sorediate soredia: in primarily marginal soralia which are elongate (usually becoming ± continuous except on the peripheral lobes), not or only partly reflexed, only rarely appearing weakly labriform, some laminal soralia sometimes also developing, especially in older thallus parts; individual soredia granular to pseudocorticate and isidioid upper cortex: scleroplectenchymatous medulla: white to off-white lower cortex: irregularly prosoplectenchymatous lower surface: peripheral lobes usually dark tan-brown, occasionally paler but almost never white, darkening to dark brown or black inwardly, dull or weakly shiny; rhizines: black and squarrosely branched Apothecia: infrequent, up to 3 mm in diam., sessile, the margin thick and entire, not usually lobulate, soon becoming sorediate ascospores: 26-32 (-35) x 13-18 (-20) µm Spot tests: cortex, medulla and soralia normally with all negative, very rarely the soralia K+ and/or KC+ slight yellow Secondary metabolites: usually none detected, variolaric acid very rarely accessory (apparently in the soralia).

Notes: This species is distinguished by the linear marginal soralia and the usual lack of positive spot tests. A similar species occurring primarily in the western part of the Sonoran Region is P. isidiigera, which is distinguished by having a paraplectenchymatous upper cortex. Both these species must also be carefully distinguished from P. enteroxantha, which can usually be identified by the positive K and KC (yellowish) spot tests in the medulla (and often also on the soralia).

Naming

Physconia detersa (Nyl.) Poelt
Physcia detersa (Nyl.) Nyl.
Parmelia pulverulenta var. detersa Nyl., 1860

Distribution

World distribution: North America, Europe, Asia.

Status

Global Status: G5

Habitat

On bark, rock, or over mosses on rock. In Ohio very common on cemetery headstones; less frequently on bark.