The lichen's photobiont (the algae or cyanobacteria involved in its symbiosis) can vary, including types from the genus Trentpohlia, the family Chlorococcaceae, or may be absent altogether.

[3] The reproductive structures resemble apothecia, a common form of lichen fruiting body, and come in various shapes, from flat to convex, and may be elongated or star-like.

They are semi-fissitunicate, meaning they have two wall layers that split during spore release, and feature a large apical dome with a distinct ocular chamber.

The ascospores are obovoid to ellipsoidal, colourless, and muriform, meaning they are divided by multiple internal walls, creating a brick-like pattern.

[3] Arthothelium typically grows on smooth bark in humid, undisturbed habitats, although it is rarely found on rock.