Placidium arboreum, commonly known as the tree stipplescale, is a species of corticolous (bark-dwelling), squamulose (scaley) lichen in the family Verrucariaceae.

[3] Fries wrote of the lichen: "In addition there is a variety, Endocarpon arboreum of Schweinitz from North America, which by its description should be referred here but from its whole structure seems to be a poorly developed Sticta".

[2] This was because in 1956, American lichenologist Mason Hale designated the name Endocarpon arboreum as a nomen nudum, which opened the way to use the epithet tuckermanii; he was apparently not aware of Michener's publication.

[9] Since Michener's description of the species was published earlier than Montagne's, it has priority, and those names (and later recombinations) with epithet tuckermanii are relegated to synonymy.

[10] Placidium arboreum belongs to the catapyrenioid group within the Verrucariaceae, characterized by over 80 lichens that are squamulose (scaley), possess simple ascospores (devoid of septa), and do not contain algae in the hymenium.

[12] In a field guide to lichens of Great Smoky Mountains National Park, the authors highlight the distinctiveness of the species due to its uniquely large squamules.

Several distinctions can be observed in Catapyrenium cinereum – its brown to black rhizohyphae, the formation of a thick, dark hypothallus, a typically densely pruinose upper surface, and clavate (club-shaped) asci.

The lichen has also been found in the West Indies and has been recorded in Tucumán, Argentina, where it was growing in a rainforest at an elevation of 1,200 m (3,900 ft).

Tree genera that associate with Placidium arboreum less commonly include Ulmus (elm), Fraxinus (ash), Carya (hickory), Platanus, Liquidambar (sweetgum), Acer (maple), and Salix (willow).