Anamorph: not known.
Teleomorph: Ascostromata 250-400 µm diam., ± globose, erumpent in linear or irregular clusters, surrounded by amorphous melanized material, with a papillate ostiole that hardly extends beyond the stromatic elements. Interascal tissue composed of of branched septate pseudoparaphyses ca 2 µm diam., tending to deliquesce at maturity. Asci 90-110 x 13-18 µm, narrowly clavate, thick-walled and fissitunicate, the stalk tapering and the apex obtuse to rounded with a poorly developed ocular chamber, 8-spored. Ascospores arranged biseriately, 26-30 x 6-8 µm, fusiform, eventually 3-septate, the primary septum strongly constricted and the secondary septa less so, the cell above the primary septum slightly broader than that immediately below, hyaline, smooth, fairly thin-walled, surrounded by a broad gelatinous sheath.
Not formally assessed, and only known from a single collection.
Similar to Massarina (now Periconia) igniaria, but with narrower ascospores and ascostromata that develop within ill-defined black stromatic material. Some collections of M. rubi have ascospores with three septa and these could be confused, but that species does not usually occur on grasses and its spores are distinctly shorter.
On a dead culm of Phalaris arundinacea.
Only recorded from a single site in VC1 W Cornwall.