Diagnosis. Differs from Acarospora subfuscescens by its reddish brown to brown apothecia that remain brown when hydrated.

TYPE: USA, California, San Bernardino Co., Joshua Tree National Park, below Belle Mountain, in unnamed wash, 34.0189°N 116.0025°W, 1382 m, common on granite boulder on wash, apothecia emerging from rock, 22 August 2005, K. Knudsen 3620 (Holotype, UCR; isotype, ASU) [editorial note by K. Knudsen & F. Bungartz: ASU does not hold an isotype specimen, but only a "topotype", i.e., a specimen collected at the same locality, but numbered as K. Knudsen 3607 (ASUL002443)].

Etymology. Named because it grows as either an endolithic lichen or a lichenicolous fungus.

Description. Thallus in non-parasitic specimens endolithic, the algal layer occurring in the substrate below the apothecia beneath a mycelial base continuous with hypothecium. In parasitic specimens endokapylic, no algal layer occurring in substrate below host, apothecia emerging from the host.
Apothecia superficial on host or occurring on substrate, brown when dry or wet, 0.5–1.0 mm diam, round or irregular, dispersed or contiguous, forming clusters of apothecia to 3 mm wide; disc brown to reddish brown, convex, with furrows, ridges, and umbos, rough and uneven, margin distinct but becoming fissured. Parathecium to 100 μm wide, hyphae mostly 2–3 μm diam, septate, cells mostly 2–3 μm wide, ending in expanded apices forming outer wall of the margin. Outer layer of margin reddish-brown to dull brown, 20–30 μm thick; inner layer hyaline. Epihymenium 10–20 μm thick, in reddish brown gel, accretions on surface of disc to 200 μm high formed from the epihymenial gel. Hymenium 80–120 μm tall, hyaline, hymenial gel IKI+ deep blue (euamyloid), paraphyses coherent (1–)2–3 μm diam, sometimes constricted at septa, infrequently branching in lower half, unexpanded or expanded apices sometimes in darker pigment caps. Asci 60–90 × 12–20 μm, ascospores mostly 100 per ascus, ascospores (3.0–)4.0–4.5(–7) × 2.0–3.0 μm, mostly broadly ellipsoid. Subhymenium hyaline, 30–50 μm thick, IKI+ blue. Hypothecium up to 50 μm thick, continuous with vegetative vertical hyphae forming a mycelial base above algal layer in substrate.
Pycnidia not seen.

Chemistry. Spot tests C–, KC–, K–. P–.

Ecology & distribution. Occurring in siliceous rock, usually granite, as an endolithic lichen or endokapylic in the thallus of crustose lichens as a non-lichenized parasite in North America (California) and Asia (Afghanistan, Xinjiang in China) (Knudsen & Kocourková 2008, 2009; L. Nurtai, pers comm.) The specimen from Afghanistan at GZU is a parasite on an unknown lichen on granite. The specimens from Xinjiang are endolithic lichens on granite. Based on the distribution of Acarospora gyrocarpa (H. Magn.) K. Knudsen & M. Westb. [≡ Polysporina gyrocarpa (H. Magn.) N.S. Golubk.] in China and southwestern United States, S. paradoxa is expected like A. gyrocarpa to be widespread but probably rare in the Chihuahuan, Mojave, and Sonoran Deserts in southwestern North America. (Knudsen & Kocourková 2009). The species is easily over-looked in field inventories.