Pleurosticta acetabulum

Pleurosticta acetabulum (formerly known as Parmelia acetabulum) is a prominent, large-thalloid foliose lichen belonging to the family Parmeliaceae (order Lecanorales).

Taxonomic Overview

• Basionym: Lichen acetabulum Neck. (1768)

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• Current Combination: Pleurosticta acetabulum (Neck.) Elix & Lumbsch (1988), following the resurrection of the genus Pleurosticta.

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• Type Species: It serves as the type species of the genus Pleurosticta.

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Morphological Characteristics

• Thallus: Foliose, loosely attached, rosette-forming, typically reaching 10–15 cm in diameter. Lobes are broad (0.5–1.5 cm wide), thick, and possess a rubber-like consistency. The upper surface is olive-green to grey-green when dry, turning bright green and glossy when moist, characteristically featuring marginal pycnidia.

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• Apothecia: Usually abundant, large (0.5–2 cm in diameter), bowl- or cup-shaped (reflecting the species epithet acetabulum, meaning a small vinegar cup or saucers), with crenulate or wavy exciple margins.

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• Photobiont: A trebouxioid green alga.

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Chemistry & Spot Tests

• Spot Tests: Cortex: $\text{C-}, \text{K+ yellow}$; Medulla: $\text{C-}, \text{K+ red}, \text{KC-}, \text{Pd+ orange}$.

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• Secondary Metabolites: Contains atranorin, salazinic acid, norstictic acid, protocetraric acid, and evernic acid.

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Ecology & Distribution

• Habitat: Primarily a corticolous species found on the bark of well-lit, nutrient-rich (eutrophic) deciduous trees—such as oak (Quercus), ash (Fraxinus), lime (Tilia), and elm (Ulmus)—along roadside avenues, orchards, and open parklands. Occasionally, it occurs saxicolously on old calcareous walls or monuments.

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• Distribution: Widespread throughout Europe and parts of North Africa (such as Algeria), showing a strongly thermophilic tendency.

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• Lichenicolous Fungi: Known to host specialized fungal parasites including Abrothallus acetabuli, Lichenoconium erodens, and Stigmidium acetabuli.