Huneckia pollinii
I am teaching a lichen ID course at the moment and feel like I have to keep reiderating "yeah these lichen features on consistent! . . . until they aren't." And reading the description for Huneckia pollinii is giving me mad consistent-until-it-is-not vibes. This lichen has a thin, crustose thallus of ashy-white to dark gray that can have an inconspicuous, immersed thallus or a more prominent cracked or warted thallus. It is sometimes surrounded in a dark prothallus. It has tiny, yellow or rusty red-brown or dark blackish-brown apothecia. These can reach sizes up to 1.3 mm across, but can also be much smaller (0.3-0.5 mm across) if H. pollinii is growing on small twigs. But it can also grow on the larger branches and trunks of smooth-barked deciduous trees (and even bone, apparently?!), and while I see 2 conflicting reports that suggest they prefer warm-temperate OR Arctic habitats, there's a good chance it grows in a bunch of different habitats but is easily overlooked or misidentified due to its small size. So yeah. Something is true until it isn't. Welcome to biology, or I guess science in general.
images: source | source
info: source | source