[Arthopyrenia fuscatae Arnold, more]
Vegetative hyphae: indistinct or composed of a few brownish hyphae of 4-5 Ám in diam. Pseudothecia: black, globose, semi-immersed, 50-100 Ám high and 50-100 Ám wide wall: upper part dark brown, lower part hyaline hamathecium: with pseudoparaphyses of type a asci: clavate to saccate, 30-40 x 10-15 Ám, 8-spored, with an ocular chamber; endoascus: I- and KI-, BCr- ascospores: hyaline, 1-septate, constricted at the septa, upper cell slightly thicker than lower one, ellipsoid, (8-)10-12 x 4-5(-5.5) Ám; walls: smooth, thin, BCr- Pycnidia: not seen. Hosts: on thallus of Acarospora subg. Phaeothallia species, mainly on Acarospora fuscata World distribution: Europe, Africa (South Africa), and North America (U.S.A. and Mexico) Sonoran distribution: in Arizona, Sonora and Baja California. Notes: Stigmidium fuscatae was often used in a wide sense including S. epixanthum. Hafellner et al. (2002) proposed using this name only for the small spored taxon on Acarospora subgen. Phaeothallia, with mostly semi-immersed perithecia of small size. Therefore the specimens cited by Triebel et al. (1991) as S. fuscatae growing on Acarospora schleicheri all belong to S. epixanthum.