[3] Species in genus Byssoloma form crustose, effuse (spreading) lichens that lack a cortex (outer protective layer).

They lack a thalline margin (a rim formed by the lichen thallus) and possess a true exciple, which is a layer of loosely arranged hyphae that can appear hairy or web-like (tomentose-arachnoid) in some species.

[4] The hypothecium, a layer beneath the hymenium, is dark red-brown and may turn purple when treated with potassium hydroxide (K) solution in European species.

They have thick walls and a blue-staining apical dome with a darker blue tubular ring structure and an amyloid (starch-like) gelatinous coat.

The conidiophores (spore-producing cells) are unbranched, forming flask-shaped, bacillar (rod-like), or ellipsoidal conidia (asexual spores) that are constricted in the middle.