Melanelixia key
| 1. | Thallus with simple or branched isidia, never associated with soredia; thallus surface glossy | 2. |
| Thallus with a mixture of soredia and ± secondarily corticate isidia; thallus surface matt | 3. | |
| 2. | Thallus black-brown, often with copious isidia which obscure the upper surface of the central part; usually on siliceous rocks | Melanelixia fuliginosa |
| Thallus green to light olive brown, with scattered or aggregated but rarely copious isidia; usually on bark or wood | Melanelixia glabratula | |
| 3. | Sorediate-isidiate areas mostly laminal, pale yellow when abraded, thallus ± closely appressed, pale cortical hairs at ends of lobes absent. Common and widespread. | Melanelixia subaurifera |
| Sorediate-isidiate areas (on the lamina and thallus edges) white when abraded, thallus often ascending at the margins, pale cortical hairs present on lobe ends. Rare, possibly extinct. | Melanelixia subargentifera |