The species epithet refers to the typically sessile propagule of diahyphae and incorporated photobionts.

Its surface is irregularly verrucose due to the presence of calcium oxalate crystals, giving the lichen a distinct appearance.

The apothecia are broadly sessile, light tan to orange-brown in color, and measure 0.15–0.3 mm in diameter.

The lichen typically produces 1–2 (rarely 4) oblong to vermiform, 11–19 septate ascospores per ascus, which measure 50–80 by 6–12 μm.

[2] Gyalideopsis sessile has been found growing on the leaf blades of Sabal palmetto in live oak hammocks, specifically in Lee County, Florida.