It has a pale olive-grey colour and typically forms continuous patches that are thin and measure between 2 and 5 cm in diameter.

[2] The photobiont of this species is from the green algal genus Trentepohlia, whose angular to rounded cells are arranged in irregular plates or short threads, each about 6–10 μm in diameter.

It is 70–150 μm broad, colourless to pale orange at the periphery, and turns sordid yellow-brown when an iodine solution is applied.

The hymenium itself is 90–100 μm high, colourless, and changes from pale blue to quickly sordid green and then reddish-brown with iodine staining.

The habitat where Coenogonium flammeum thrives is characterised by forests dominated by trees from the families Myrtaceae and Lauraceae, and the genus Podocarpus.