Originally circumscribed in 1817,[2] the genus consists of crustose and squamulose lichens with green algal photobionts, biatorine apothecia, colorless, simple to 3-septate ascospores, and bacilliform pycnospores.

Their colour varies widely, including light beige, dark reddish brown, green-grey, bluish green, or khaki.

It consists of tightly packed, radiating hyphae embedded in a gel matrix that remains stable in potassium hydroxide (K) solution and does not swell.

The hymenium, where spores develop, is 30–100 μm tall and typically lacks a distinct epithecium (uppermost layer), though some species show pale pigmentation at the top.

It does not contain granules or oil droplets and reacts with iodine (I+), staining red-brown when young and blue in older herbarium specimens.

The hypothecium, a supporting tissue beneath the hymenium, consists of interwoven hyphae embedded in a dense gel matrix.

[4] The paraphyses, sterile filamentous structures within the hymenium, are coherent in KOH, have narrow lumina (0.5–2.5 μm wide), and are mostly unbranched, though occasional branching or connections (anastomoses) occur.