Pea-green Shield Lichen

The foliose (leafy) thallus of Parmelia fraudans is tightly attached to its substrate, typically measuring 4–16 cm (1.6–6.3 in) in diameter. The brittle, flat lobes that comprise the thallus range from contiguous to overlapping, and are 1–4 mm wide, with truncated tips. The colour of the upper thallus surface is grey to yellowish grey, while texturally it is smooth to delicately pitted, with pseudocyphellae and soredia. The soredia, which somewhat resemble isidia, are abundant and are concentrated along the margins of the thallus. The medulla is white. The thallus undersurface is black in the centre, becoming brown towards the margins. Numerous black rhizines (both branched and unbranched) act as holdfasts. Apothecia are rarely observed; when present, they measure 2–4 mm in diameter and have a dark brown disc, with soredia typically on the apothecial margin. The ascospores have an ellipsoid shape and measure 10–12 by 5–6 μm. The expected results of standard chemical spot tests on Parmelia fraudans are cortex K+ (yellow), C−, KC−, P+ (yellow); medulla K+ (yellow becoming deep red), C−, KC−, and P+ (orange). Secondary compounds found in the lichen are atranorin and chloroatranorin in the cortex (and sometimes usnic acid in the soralia), and salazinic acid as a major component of the medulla, with minor amounts of consalazinic acid and protolichesterinic acid. …

Parmelia fraudans occurs in Europe and North America, where it grows on rocks. Its North American distribution extends from Alaska south to Mexico. Although it is generally rare in Eastern Canada, it was reported as new to Nova Scotia in 2022. In Europe, it has been recorded from the Czech Republic, Estonia, France, Finland, Greenland, Norway, Russia, Sweden, and Slovakia. In the 2019 red list of Estonian lichens, it was classified as a critically endangered species due to a reduction of its range and a decrease in population size (compared to its 2008 assessment).

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