Found in northern North America, it was formally described as a new species in 1976 by lichenologist Leif Tibell.

The expected results of chemical spot tests are KC− on the thallus, and K+ (red), P+ (yellow) on the mazaedia.

When a long-wavelength UV light is lit on the thallus, it fluoresces a blue-white color.

The ascospores of the lichen are spherical and lack any septa; they measure 14–16 μm.

[1] Endococcus thelommatis is a lichenicolous fungus that parasitizes Thelomma santessonii.