Key to Dimelaena species with usnic acid:

1. Marginal lobes convex, loosely attached to the substrate; edges of the areolae usually dark; pycnidia numerous ............. D. oreina

- Marginal lobes plane and closely attached to the substrate; edges of the areolae rarely dark; pycnidia rare ....................................2

2. Apothecia adnate and apothecia margins obvious, upper surface grayish-yellow, with whitish pruina ............................. D. tibetica

- Apothecia innate and apothecia margins absent or not obvious, upper surface yellowish-green, without pruina........... D. altissima