Mucomycosphaerella eurypotami(Kohlm., Volkm.-Kohlm. & O.E. Erikss.) Quaedvl. & Crous, in Quaedvlieg, Binder, Groenewald, Summerell, Carnegie, Burgess & Crous, Persoonia 33: 22 (2014)

Index Fungorum number: IF 807792; MycoBank number: MB 807792; Facesoffungi number: FoF 09727

Basionym – Mycosphaerella eurypotami Kohlm., Volkm.-Kohlm. & O.E. Erikss., Bot. Mar. 42, 6: 505. 1999.

Etymology – From the Greek meaning broad and river, in reference to the type locality, Broad Creek (Carteret County, North Carolina) of this and most other fungal species described from J. roemerianus.

Sexual morph: Ascomata 115–130 μm high, 190–300 μm wide, depressed ellipsoidal, at first immersed, then breaking through the epidermis, ostiolate, epapillate, coriaceous, brown, dark brown at the ostiole, gregarious, sometimes two or more joined together (Figs 1, 2, 4). Ostiole 55-70 μm in diam. Peridium 12-18 μm thick around the ostiole, 6-7 μmat the side and base, composed of 4-6 layers of cells at the top, 2-3 layers at the side and base, forming a textura angularis in longitudinal section; ascomata partly covered by a layer of brownish hyphae in textura intricata. Hamathecium sparse, composed of branched and anastomosing, septate pseudoparaphyses, 2-3.5 μm in diameter, embedded in a gelatinous matrix, forming a tight tissue around the asci (Figs 2, 4). Asci 42-54 3× 17-22 μm, 8-spored, ellipsoidal to ovoid (Fig. 5), indistinctly pedicellate, bitunicate, fissitunicate, thick-walled, with a thin, tough ectotunica and a thick gelatinous, expanding endotunica; the endotunica is thickest in the upper parts, when treated with KOH it swells considerably and a conspicuous ocular chamber can be seen; when the ectotunica is broken at the tip, the endotunica elongates, and a short truncated foot becomes visible (Fig. 6); without apical apparatus, not blueing in IKI, maturing successively on the ascogenous tissue at the bottom of the locule (Figs 1, 2, 4). Ascospores 23-29 × 5.5-6.5 μm (x¯= 25.7 × 6.1 μm; n = 35), bi- to triseriate, elongate ellipsoidal, sometimes inequilateral, one-septate, one additional pseudoseptum in each cell, slightly constricted at the septum, upper cell wider and more pointed than the lower one, hyaline, both hemispores containing two to three oil globules, surrounded by a gelatinous sheath that is constricted around the septum; in KOH the cells round off a little at the septum and may even separate here; treatment with Lugol’s solution does not result in any change (Figs 3, 7, 8)

Specimen examined – USA, North Carolina, Virginia, Carteret County, Broad Creek, N34°43′, W76°55’07”, on senescent leaves of Juncus roemerianus, 21 May 1996, B. & J. Kohlmeyer (holotype JK5586 in IMS, culture ex-type JK5586J).

Notes — Mucomycosphaerella is distinguished from Mycosphaerella s.str. by having well developed, persistent mucoid sheaths around its ascospores, and the absence of Ramularia asexual states. Its ascomata are depressed, and have a pale, thin-walled lower half, and a hamathecium of loosely branched, anastomosing hyphae in a hymenial gel, with hyaline ascospores (). Mucomycosphaerella eurypotami was included in Mycosphaerella as a temporary measure, until a formal revision of the genus (), which has been ongoing since the epitypification of the type species (), and the segregation of various allied genera and families ().

Figure 1 – Mycosphaerella eurypotami. 1, 2. Longitudinal sections (8 mm) through ascomata. 3 Ascospores with gelatinous sheaths. Scale bars: 1 and 2 = 20 μm, 3 = 10 μm.

Figure 2 – Mycosphaerella eurypotami. 4. Longitudinal section (8 mm) through part of young ascoma. 5. Mature asci. 6. Ascus; ectoascus ruptured at the apex, endoascus expanded; a small foot has become visible. 7 and 8. Ascospores with gelatinous sheaths. Scale bars = 10 μm.