Subiculum well-developed, dark brown to reddish brown, purple, densely woolly, sometimes felty with age, covering young stromata completely, becoming gradually reduced, in age often present around the stroma bases, sometimes absent between stromatal groups but persistent at the edges of the colony and forming large webs around them.
Anamorph: conidiophores appearing as light grey brown areas in the subiculum, to 150 µm long, di- and trichotomously branched, hyaline to light brown. Conidiogenous cells to 55 x 5 µm, with intercalary conidiogenous regions, hyaline to light brown. Conidia 5.5-11.5 x 4-5 µm, ellipsoidal with a truncate base, hyaline to light brown.
Teleomorph: stromata (0.7-) 1-1.5 (-1.9) mm diam., (0.5-) 1-1.5 (-1.7) mm high, usually semiglobose with a ± flattened top, with finely papillate to slightly pointed ostioles, the base often with a short broad stipe remaining completely embedded in the subiculum, dark brown to reddish brown with black ostioles, turning completely black when old, forming in clusters, sometimes fused and thus appearing to contain 2-3 perithecia. Outer stromatic layer (75-) 100-125 (-150) µm thick, black, hard. Inner stromatic layer initially cream-coloured to light brown, later turning dark brown to black around the perithecia. Perithecia gradually detaching from the stromatal wall. Asci 170-230 x 10-20 µm, the spore-bearing part 140-180 µm long, the stipe gradually tapering, not fissitunicate, with a large conspicuous structure blueing in iodine, 6-11 µm tall high and 4-6 µm diam. that is sometimes slightly constricted in the mid portion, 8-spored. Ascospores 19-34 x 7-14 µm, ellipsoidal to slightly ovoid, often asymmetric, dark brown, with a straight or slightly diagonal germ slit nearly the spore length, with a broadly rounded cellular appendage 1-3 µm diam. and high at one and rarely both spore ends, the whole spore surrounded by a gelatinous sheath to 2 µm thick at the sides and to 4 µm thick at the ends, breaking down in old material.
Not formally assessed; there are few records in GBI but the species may be mistaken for other Rosellinia species. It would be considered as Data Deficient.
Similar to Rosellinia aquila which also has a well-developed subiculum, but with slightly longer ascospores that are surrounded by a gelatinous sheath.
In GBI, on rotten branches of Acer pseudoplatanus and Quercus robur; elsewhere known from a range of other broadelaves trees.
In GBI, reported from VC1 W Cornwall, VC21 Middlesex, VC63 SW Yorkshire and VC H38 Down (N Ireland).