Pleosporales » Massarinaceae » Byssothecium

Byssothecium flumineum

Byssothecium flumineum J.L. Crane, Shearer & Huhndorf

Index Fungorum number: IF 358079

Holotype: ATCC 44622

Etymology: belonging to a river


Saprobic on submerged decaying wood in freshwater habitats. Sexual morph: Ascomata numerous, scattered to clustered, superficial or immersed, subglobose becoming ovoid to obpyriform at maturity, papillate, uniloculate, with light brown, septate, flexuous hairs in culture, (309–)342–428(–530) μm long, 204–300(–338) μm wide. Beak central, conical to somewhat cylindrical, rounded at apex, (105–)115–215(–225) μm long, (40–)45–85(–90) μm wide at apex, (75–)80–145(–165) μm wide at base. Ostiole (40–)50–70(–75) μm diam, with periphyses. Wall composed of 5–7 layers of polygonal cells, 20–40(–46) μm thick, somewhat thinner at base, surface of textura angularis, with no external crusts, cells prosenchymatic to pseudoparenchymatic. Pseudoparaphyses cellular, at first entangled then parallel, branching and anastomosing, attached at top and bottom of centrum, in a gelatinous matrix, 1–2 μm wide, septum interval (9–)11–20(–23) μm. Asci numerous, basal and slightly lateral, partially lining the peripheral wall of the centrum, cylindrical to clavate, slightly narrowed at base, rounded and undifferentiated at apex, 8-spored, biseriate at apex, becoming uniseriate at base, short-stalked, bitunicate with fissitunicate dehiscence, 80–112(–115) × 10–15 μm. Ascospores fusoid, straight or slightly curved, light brown, verrucu1ose, end cells paler and rounded, subapical cell slightly enlarged, basal cell tapered, 3-septate, evenly distributed in sequence 2: 1:2, strongly constricted at midseptum, 24.2–30.8(–33) × (6.6–)7.3–9.2(–11) μm. Asexual morph: Undetermined. (Descriptions from Crane et al. 1992)


Material examined: On twigs of Prunus serotina Ehrh. submerged in Jordan Creek, Illinois, Vermilion County, from 4 June 1978 to 5 May 1979, leg. C. A. Shearer, J-52-1, ILLS 49691. Isotype: NY. Culture from the Holotype: ATCC 44622.


Notes: Byssothecium was erected by Fuckel (1861) and reinstated by Boise (1983) for B. circinans Fuckel, a saprobe or weak parasite on woody substrates, including Medicago sativa L. Boise (1989) included a second species, B. alpestris (Toth) Boise, distinguished by larger ascospores. Byssothecium jlumineum shows affinity with B. circinans in having immersed to erumpent, ovoid to obpyriform, broadly papillate ascomata with a pseudoparenchymatous peridium composed of small polygonal cells and ascospores similar in shape and coloration which aggregate about the ostiole in ascomata formed in culture. Byssothecium flumineum differs by having narrower ascospores which are not encrusted with a dark pigmented substance. Ascospores of B. flumineum are verruculosely ornamented, a characteristic not noted in B. circinans, but which may be present in B. alpestris (Boise, 1989). Unlike B. circinans, B. flumineum has not formed an anamorph in culture.