A lichen very similar to P. perlatum, from which it differs in wider lobes (>10 mm), longer cilia (up to 3 mm) and especially in lichen substances in the medulla, which react K–, KC+ red and UV+ blue-white, as it contains alectronic and α-collatolic acids.
It usually grows on horizontal branches in well-preserved moist forests (Cannon et al. 2023), often in the tree canopy (Nimis et al. 2018). Parmotrema arnoldii is a widely distributed species worldwide, mostly in oceanic areas with temperate climates (Elix & Thell 2011). It was only published as new to the Czech Republic in 2023, when it was discovered during a revision of historical material (Šoun 2023). The record comes from the bark of Alnus incana in the Lomná valley, probably from Dolní Lomná, in the Beskydy Mountains.
Literature: Cannon P. et al. (2023): Lecanorales: Parmeliaceae. – Revisions of British and Irish Lichens 33: 1–98. Elix J. A. & Thell A. (2011): Parmotrema. – In: Thell A. & Moberg R. [eds], Parmeliaceae, Nordic Lichen Flora 4: 94–97. Nimis P. L., Hafellner J., Roux C., Clerc P., Mayrhofer H., Martellos S. & Bilovitz P. O. (2018): The lichens of the Alps – an annotated checklist. – Mycokeys 31: 1–634. Šoun J. (2023): Revize historických položek rodu Parmotrema z území ČR uložených v herbáři PRM. – Bryonora 72: 23–33.
taxonomic classification:Ascomycota → Lecanoromycetes → Lecanorales → Parmeliaceae → Parmotrema
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