Sclerotia 4-5 x ca 1 mm, fusiform-ellipsoidal to slightly banana-shaped, black, with irregular longitudinal ridges when dry, with an outer layer of very thick-walled dark brown globose to angular cells 7-12 µm diam. and an inner layer of degraded ± hyaline epidermoid cells containing remnants of plant tissue.
Anamorph: not known.
Teleomorph: ascomata apothecia, emerging singly from sclerotia, 3-4 mm diam., discoid to shallowly cupulate, pale brownish yellow to brownish orange, very long-stalked, the stipe 15-20 mm long, pale yellow-brown, the basal part blackened. Ectal excipulum composed of thin-walled globose cells 9-18 µm diam., not gelatinized. Medulla composed of rather irregular profusely branched thin-walled hyphae. Interascal tissue of unbranched thin-walled hyaline paraphyses 2-3 µm diam., the apices 4-5 µm diam., clavate, without a gelatinous matrix. Asci 60-80 x 6-7.5 µm (fresh material), 58-65 x 4.5-5.5 µm (dried material), cylindrical, short-stalked, fairly thick-walled but not fissitunicate, the apex rounded to truncate, conspicuously thickened with a J+ apical ring 1-1.5 µm diam. and 2-3 µm tall, 4-spored (4- to 8-spored in extralimital collections). Ascospores arranged ± uniseriately, 8-9.5 x 3.5-4 µm (dried material) [9.5-12 x 3-5 µm in fresh, extralimital material], fusiform-ellipsoidal to ellipsoidal, sometimes slightly ovoid, thin-walled, hyaline, aseptate, smooth, without a gelatinous sheath or appendages.
Not formally assessed, but the species appears to be rare. It has only been recorded once from GB&I; more information about its ecology would be needed to make a formal assessment.
There are few four-spored members of the Sclerotiniaceae; Lindemann (2011) provides a key to five species showing this feature; all have larger ascospores except for Ciboria acerina which forms indeterminate crust-like sclerotial structures. The phylogenetic significance of the four-spored ascus is likely not to be very significant; extralimital collections have been found with variable numbers of spores in the ascus. The eight-spored species Myriosclerotinia dennisii (syn. Sclerotinia gregoriana) is similar in most respects; that species is associated with Eleocharis, Eriophorum and Scirpus.
In GB&I, found in a boggy area under Salix and Alnus, but there is no direct evidence of a nutritional link with either of these plants.
In GB&I, found at one site in VC62 NE Yorkshire; otherwise scattered through northern central Europe but apparently rare in all areas.