Tetramelas gariwerdensis is named after its type locality in the Gariwerd (Grampians mountain range) in Victoria, Australia.

The individual tile-like sections (areoles) vary in shape from round to irregular or angular and range in size from 0.3 to 1 mm wide.

[1] The white medulla, or inner layer of the thallus, does not contain calcium oxalate as indicated by its lack of reaction to sulfuric acid, but it does react to iodine, turning pale purple.

These apothecia can be found separately or in small groups, either broadly attached (adnate) or slightly raised (sessile) on the thallus.

The apothecia's disc is black, non-powdery (epruinose), and its shape varies from weakly concave to flat or even convex, becoming wavy (undulate) as it ages.

[1] The paraphyses (slender filaments within the hymenium) are 1.5–2 μm wide, with simple to sparsely branched structures that have dark brown capped tips.