Aspicilia (aka “Sunken Disk Lichens”)
Description: Usually crustose, although sometimes comes in fruticose forms with gray, white, or greenish thalli & immersed, pure black apothecia (sometimes hidden by pruina). Photobiont green (unicellular). Apothecial disks more or less flush with the thallus surface or with a slightly raised, lecanorine rime; hypothecium & exciple colorless, epihymenium pale green to olive-brown; tips of the paraphyses composed of short, rounded cells that look like a string of beads, asci K/I-, the tip only slightly thickened; spores colorless, 1-celled, ellipsoid to subspherical (9-40 x 6-20 um), not halonate, 4-8 per ascus; conidia long, straight, & thread0like.
Chemistry: Often containing B-orcinol depsidones such as norstictic & stictic acids; others with fatty acids or triterpenes
Substrate: On rocks of all kinds, in sun or shade.
Lookalikes: The variability of the species of Aspicilia in both thallus morphology & chmistry makes this an especially difficult group to identify As the taxonomy has never been adequately worked out for North American species, distribution maps are either not presented here or should be regarded as tentative. The pale exciple, large spores, & beaded paraphyses distinguish Aspicilia from other genera with immersed, disk-like apothecia, such as Bellemeria, lecidea, Amygdalaria, & Acarosporta. (see also notes on Lecanora oreinoides under Buelia spuria). Hymenelia & Ionaspis are closely related but generally have smaller spores, paler apothecia (with different pigments if black), & lack lichen substances in the thallus.
Bibliography: Lichens of North America, by Brodo, Sharnoff, & Sharnoff
Database Entry: Distance Everheart 12-26-13