[2] Lecidea lygommella forms a crust-like thallus that can spread up to 7 cm wide and is relatively thin, ranging from 0.2 to 0.7 mm in thickness.

The upper surface of the thallus varies in colour from whitish and pale grey to a rusty red-brown.

They are rounded to angular in shape, and range from being slightly embedded in the thallus to sitting on top of it, spanning 0.5–2.3 mm in width.

[2] The hypothecium, the tissue layer beneath the hymenium, is dark brown to black-brown at the base and turns violet-brown when treated with potassium hydroxide (K+).

The epihymenium is brownish green, about 10–15 μm high, and turns red-violet when treated with nitric acid (N+).

Pycnidia (asexual reproductive structures) are immersed in the thallus, with black, punctiform (point-like) ostioles.