Phaeospora rimosicola
Anamorph: not known.
Teleomorph: ascomata perithecial, 60–130 (–180) μm diam., black, subglobose, scattered or in small clusters, initially immersed but becoming erumpent in the upper part. Vegetative hyphae 1–3 μm diam., immersed, brownish, septate, branched, thin-walled. Peridium brown, 8–10 μm thick, composed of several layers of polygonal cells 4–8 μm diam., externally with a thin, dark wall, internally hyaline, lower part covered with numerous elongate vegetative hyphae. Hymenium I+ red, KI+ blue (especially in the basal parts). Interascal tissue absent, periphyses short, simple to 1-septate, 2–3 μm diam. Asci 70-85 × 9–12 μm, cylindrical to cylindric-clavate, short-stalked, the wall thickened in the apical part, fissitunicate, not staining in iodine, (4-) 8-spored. Ascospores obliquely uniseriately to biseriately arranged, (14-) 16-17.5 (-19) × 5-7 μm ((16-) 20 (-22) x (6.5) 8 (-9) fide Hawksworth et al. 2010), ellipsoidal to clavate, with obtuse apices, soon light grey to golden brown inside the asci, 3-septate, strongly constricted at the septa, with many small oil guttules, smooth, with a conspicuous epispore 1-1.5 µm in thickness.
Assessed by Woods & Coppins (2012) as of Least Concern, though listed as Nationally Rare. It is probably under-recorded.
Similar to Phaeospora parasitica, but with somewhat smaller ascospores. Spore measurements in the literature vary considerably, possibly because the epispore varies in thickness depending on the mounting medium and may not be included.
Parasitic on Rhizocarpon species, especially R. petraeum and R. umbilicatum, apparently causing little damage to the host.
Scattered throughout upland areas of northern England and Scotland. BLS map here.