Ascomata 400-700 µm diam, the body globose to slightly oblate, at first immersed with only the neck protruding but sometimes becoming superficial due to degradation of host tissues, matt black, the neck strongly papillate, conical, to 250 µm in length, periphysate, in some collections with the emergent part covered in chestnut brown thick-walled setose hairs to ca 15 µm diam at the base and to 115 µm in length. Peridium composed of several layers of pale brown irregular rather thin-walled textura angularis with cells to 12 µm diam, the innermost layer ± hyaline. Interascal tissue of paraphyses, filiform, thin-walled, septate, sometimes longer than the asci, usually deliquescent at maturity. Asci 150-250 x 15-50 µm, cylindrical, with a narrow stalk to 100 µm in length, fairly thin-walled at all stages, the apex rounded with a funnel-shaped J- apical ring, apparently sometimes fracturing below the apex, 8-spored. Ascospores arranged obliquely uniseriately, 33-38 x 19-23 µm, ellipsoidal, dark brown and thick-walled, smooth, with a thin median septum, with two prominent persistent conical apical appendages 2.5-5 µm in length and with a similar diameter.
The ascospore appendages are unusually persistent, but appear not to be cellular in nature. Ascus dehiscence was described as circumscissile with all the spores ejected as a single propagule by Shearer et al. (1980), but this may have been an artifact associated with the cultural conditions. They also reported that the ascospores are minutely ornamented when viewed with the SEM, though perhaps it is derived from the cytoplasmic contents of the ascus rather than the ascospore wall.
Rather distinct in morphological terms from most species of Arnium; perhaps the similarities are convergence. The genus requires revision using molecular methods
In GBI, erumpent from dead herbaceous stems, including Arctium minus, Heracleum sphondylium and Urtica dioica
GBI: recorded from England: Devon, Suffolk, Sussex. Otherwise known only from USA (South Dakota).