The lobes of the thallus can be narrow or broad, often elongated and intricately branched, with a flat or concave surface that can be smooth or distinctly ridged or folded.

[3] The thallus is composed of intertwined hyphae intermingled with chains of photobiont cells, and it lacks both upper and lower cortex.

The reproductive structures, called apothecia, display a pale brown, red-brown, or brown-black disc surrounded by a thalline margin that is typically long-lasting.

[3] The asci, or spore-producing structures, are club-shaped (clavate) with a significantly thickened apex that reacts blue with iodine, as does the downwardly projecting annulus and apical cap.

Lathagrium produces eight spores per ascus, which are septate and primarily submuriform, but can also be spindle-shaped or cylindrical with only transverse septa.