Anamorph: conidiomata absent. Conidiophores as lateral and terminal branches from vegetative hyphae and reduced to conidiogenous cells, (6-) 10-30 x 2.5-4 (-5) µm, straight or geniculate, smooth, hyaline, proliferating sympodially with 1-3 apical loci, flattened or protuberant, cylindrical; scars thickened, darkened, refractive, ca 1 µm diam. Primary conidia 6-15 x 2-4 µm, subcylindrical to ellipsoidal or ovoid, 0- to 1-septate, hyaline, smooth. Intercalary conidia (4-) 7-10 (-15) x (3-) 4-5 µm, ellipsoidal to ovoid, 0- to 1-septate, hyaline, smooth, in branched chains of up to six conidia; hila thickened, darkened, refractive, 0.5-1 (-1.5) µm diam. A spermatial state has been reported with dark brown to black ostiolate conidiomata producing hyaline bacillar conidia 3–4 (–5) x 1–1.5 µm in size.
Teleomorph: stromata absent. Ascomata in extensive clusters, 110-130 µm diam., ± globose, immersed in dead leaf tissue with a fairly broad black papillate erumpent ostiole 60-80 µm diam. Peridium composed of 2-3 layers of large dark brown thin-walled globose cells mostly 7-8 µm diam. Interascal tissue absent. Asci formed in a basal fascicle, 32-37 x 5.5-7 µm, cylindrical to saccate, almost sessile, the apex rounded, thick-walled and fissitunicate with a relatively broad ocular chamber, not staining in iodine, 8-spored. Ascospores arranged biseriately, (7.5-) 8.5-10 x (2-) 2.5-3 µm, fusiform-clavate, slightly constricted at the ± median septum, the upper cell rather broader, hyaline, thin-walled, smooth, without an epispore, gelatinous sheath or appendages.
Not formally assessed, but the species is very common and definitely not threatened.
In dead leaves, especially of Quercus spp. Collections from Fagus are now referred to R. unterseheri. and those from other host genera may not be conspecific with R. endophylla.
Throighout the British Isles, from southern and southwestern England to Skye and the Outer Hebrides.