CANADA: Ontario, on Scirpus occidentalis, coll. H. S. Jackson et al., 4.x.1933 (NY ex TRTC 4760). GERMANY: coll. Winter, v.1874, ex Herb. Thumen (NY); Bavaria, on Scirpus lacustris, coll. A. Vill, iv.1909, Sydow, Myc. Germ. No. 984 (PDD); Berlin, on Scirpus lacustris, coll. P. Sydow, ix.1886 (NY); on Scirpus lacustris, ex Herb. Barbey-Boissier No. 975 (NY); on Scirpus lacustris, coll. G. Winter, vi.1874, de Thumen Myc. Universalis No. 178 (NY); on Scirpus lacustris, coll. J. Kunze, iv.1879, Kunze, Fungi selecti exsiccati No. 277 (NY); on Scirpus lacustris, coll. Krieger, xi. 1911, Rehm Ascomycetes No. 1953 (NY). SWEDEN. Fries, Fungi Sueci No. 170 (K). USA: Washington, Seattle, on Scirpus lacustris var. occidentalis, coll. A. M. Parker, x.1892, Ellis & Everhart, North American Fungi No. 3038 (PDD, NY); Dakota, on Scirpus sp., coll. J. F. Brenkle, 9.x.1910, Fungi Dakotenses No.142 (NY); North Dakota, on Scirpus lacustris, coll. J. F. Brenkle, v.1908 (NY); California, Lake County, Bogg's Lake, on Scirpus acutus, coll. L. Bonar, 24.viii.1945, Californian Fungi No. 644 (NY); Washington, Seattle, on Scirpus lacustris var. occidentalis, coll. C. V. Piper, x.1892, Ellis & Everhart, Fungi Columbiani No. 328 (NY); Massachussets, Essex, on Scirpus lacustris, viii.1890 (NY).

Ascomata developing in slightly paler areas of the leaves, sometimes surrounded by narrow, black zone lines. Associated with anamorph conidiomata.

In surface view ascomata 0.8-3(-7) x 0.5-0.8 mm, elliptic to broad-elliptic in outline, with rounded ends. In unopened ascomata the wall is uniformly black, usually developing a fold-like ridge along the long axis of the ascomata. Ascomata opening by an elongate split which usually forms more or less along the fold-like ridge. No differentiated zone visible along the edge of the opening split. Parts of the upper wall adjacent to the opening split often break off and fall away, leaving the hymenium partially exposed.

Ascomata develop between the host cuticle and epidermis, although when ascomata develop over stomata in the host leaf, hyphae invade and break down a few host cells immediately below the stomata. In vertical section, at an early stage of development, the ascomatal initial comprises 2-3 layers of hyaline plectenchyma, covered with a single layer of brown, thick-walled, angular cells, which comprises the first stage in the development of the upper wall (Fig. 2A). As the ascomata develop the upper wall thickens to 20-30 µm, comprising thick-walled, brown, angular cells, and a cavity develops within the hyaline plectenchyma, with paraphyses growing upward from the base of this cavity (Fig. 2B). From this stage the upper wall does not become thicker, but it darkens and becomes distorted and folded by the pressure exerted from the developing hymenium. The upper wall shows no internal differentiation, comprising uniformly thickened and darkened, angular cells, but shows a distinct upward fold near the centre of the ascomata (Fig. 2C). The upper wall splits open in the region of this fold (Fig. 2D). No layer of differentiated cells is present along the edge of the opening split. A darkened lower wall does not develop, the hyaline tissue below the hymenium resting directly on the more or less intact epidermal cells of the host.

Paraphyses 1.5 µm diam., swelling more or less abruptly to 4-6 µm diam. at the clavate to knob-like apex. Asci 130-160 x 15-18 µm, clavate, tapering gradually to rounded apex, wall at apex sometimes slightly thickened with indistinct central pore, 8 spored, spores extending two-thirds down the ascus, maturation sequential. Ascospores 40-75 x 4.5-6.5 µm, tapering slightly to both ends, 0-1 septate, surrounded by narrow gelatinous sheath.

Conidiomata 0.2-0.3 mm diam., round in outline, dark brown to black, pustulate, subcuticular. In vertical section lenticular in shape, upper wall 3-5 µm thick, comprising dark brown material without obvious cellular structure. Darkened lower wall absent, the conidiogenous layer developing on 2-3 rows of thin-walled, hyahne, angular cells. Conidiogenous cells 9-15 x 2-3 µm, cylindric, solitary, forming a palisade-like layer, with sympodial proliferation, often with more than one developing conidium held at the apex. Conidia 3-4.5 x 1 µm, oblong-elliptic with rounded ends, or short-clavate with a broadly rounded apex and tapering to a truncate base, hyahne, 0 septate.

Northern Europe and northern North America (Powell 1974).

Dead leaves of Scirpus.