The species epithet, seokpoensis, is derived from the Seokpo area on Ulleungdo Island, referencing the location where it was first discovered.

The thallus surface is continuous or with small cracks, which are up to 0.05 mm wide and confined to the cortical layer and algal zone.

Its upper surface is dull greyish, dirty whitish-grey, or greenish, and can become yellowish-green when treated with potassium hydroxide solution.

The disc of the apothecia is generally even and ranges in colour from greyish or grey-brownish-yellow to blackish-yellow, contrasting with the lighter edge.

Unlike Y. galbina, Y. seokpoensis does not show a yellow reaction to potassium hydroxide, indicating the absence of atranorin in its thallus.

Furthermore, Y. seokpoensis has larger ascospores and lacks the schizidia-like isidia and irregularly shaped thalline grains found in C. pulcherrima.