ASCOMYCOTA | LECANOROMYCETES > LECANORALES > Parmeliaceae

Genus Parmotrema, meaning 'Parmelia with holes' - from the frequently perforated apothecia

Common name:            Pearly Lichen

Synonyms:                    Parmotrema chinense, Parmelia perlata

Habitat:                         Woodland and wayside trees (for this entry)

Substrata:                     Bark and rock

Growth form:                Corticolous and Saxicolous

Thallus:                  Foliose

Apothecia:                    Lecanorine, but rare

BLS identity rating:        Graded 1/5 (identification should be straightforward)

Thallus forming a rosette, more or less regular in shape, to 15cm dia; lobes smooth, 3-8mm broad, more closely attached and more distinctly wrinkled centrally than found in the similar, albeit, much rarer Parmotrema arnoldii, incised, covered with a hem-like rim of continuous globose soralia, resulting in undulating and slightly rolled-back margins, often with black cilia up to 2mm long; upper surface typically pearly-grey when dry, more greenish-grey when moist, lower surface blackish with simple tan-coloured rhizines that do not extend to the edges of the lobes.

Rarely fertile but, if apothecia are present, discs brownish with an uneven and partially sorediate thalline margin.

If the cortex is scraped, a drop of K on the exposed white medulla will turn yellow-orange, which helps to distinguish from the rather similar-looking Hypotrachyna that have a KC+ red reaction

Common and widespread across the south and west, somewhat scarcer further north; occurring on well-lit neutral to lightly acidic-barked broadleaved trees, also frequently found on coastal rocks, and inland siliceous rocks and walls. The form that occurs on the bark of the trunk and branches of trees is generally a greener colour than specimens found on rocks.