[3] The genus Siphulastrum comprises lichens that have a small, leaf-like (foliose) to scale-like (squamulose) thallus, which can be either smooth or covered with tiny bumps and warty projections.

The underside lacks a protective layer (ecorticate) and is pale brown, attaching to the substrate through root-like structures called rhizohyphae, which can be white to blue-black in colour.

The layer beneath the apothecia (hypothecium) ranges from pale to deep yellow-brown and intensifies in colour when treated with potassium hydroxide solution (K).

[4] While Siphulastrum is similar to some other taxa in the Pannariaceae, such as some Pannaria species, Fuscopannaria, and Parmeliella, it can typically be identified by a unique combination of features.

These include the presence of argopsin in its thallus (which turns orange when tested with paraphenylenediamine), its partnership with Scytonema algae (rather than Nostoc), its disc-shaped apothecia without a defined rim, and its distinctive spore-producing sacs that partially react with iodine.