Identification
This striking lichen resembles a scattering of neon-yellow cracked pavement across sun-bleached stone. *Acarospora ochrophaea* forms a "squamulose" thallus—a crust made of tiny, angular, scale-like plates. Each squamule is a vibrant sulfur-yellow to chartreuse, often featuring a slightly waxy or "pruinose" finish. To tell it apart from the similar *Acarospora socialis*, look for its smaller, more tightly packed scales and its distinctive "eyes": small, sunken, reddish-brown fruiting bodies (apothecia) that sit flush within the yellow scales. While other yellow crusts like *Pleopsidium* have lobed edges that look like tiny fans, *A. ochrophaea* maintains a more uniform, "cobblestone" appearance.
Habitat & Range
A true sun-worshipper, this species is "saxicolous," meaning it lives exclusively on rock. It prefers non-calcareous (acidic) substrates like granite, gneiss, and rhyolite. You will find it clinging to exposed vertical faces and the tops of boulders in arid, high-light environments. It is a hallmark of the American West—thriving in the Great Basin and Mojave deserts—but it also haunts high-elevation alpine ridges across Europe and Asia where the UV radiation is intense.
Behaviour
In the field, you’ll notice this lichen is a master of "cryptobiosis." During long droughts, it becomes brittle and dormant to survive the scorching heat. However, after a desert rain, the thallus hydrates almost instantly, the yellow pigments intensifying as the internal algae spring into action. It grows with agonizing slowness, often expanding only a fraction of a millimeter each year, making a colony the size of a silver dollar potentially decades old.
Diet
As a symbiotic organism, it doesn’t "hunt" in the traditional sense. Instead, it functions as a microscopic greenhouse. The fungal partner provides the structural "house" and mineral protection, while its internal green algae (*Trebouxia*) photosynthesize sunlight into sugars. It also practices "bio-weathering," secreting oxalic acids that slowly dissolve the rock surface to anchor itself and extract trace minerals.
Fascinating Fact
While most "cup fungi" and lichens produce exactly eight spores per sac (ascus), *Acarospora* is an overachiever. A single microscopic sac in this species can contain over 100 spores, turning each tiny brown "eye" into a high-pressure spore cannon designed to colonize distant, isolated boulders.