Prosthecium stylosporum (Ell. & Ev.) Wehm.
Specimen Number AC – 2469,1480 and 214.On dead/dying twigs attached to small tree or shrub of Acer spicatum. Several collections from the same site were made over the course of 14 years (May-July)
AC 214 – spores 40-42×12µm hyaline at first but soon turning brown, 3-septate, thick-walled or with thick gel sheath, asci 8-spored; ascomata erumpent in a valsoid cluster in stroma (brown). AC 1480 -spores 2-3 septate, brown, 30-36×9-11µm, with small gel appendages at each end. Spores a bit smaller than AC-214. AC 2469 – ascomata (2-5) clustered beneath periderm, cracking bark with just ostioles showing, no stroma, no blackline; spores 3 sometimes 4 septate with gel pad-like appendages, hyaline to pale gray, 31-35×10-12µm; asci irregularly bi-multiseriate, 80-100×19-22µm. Two other specimens (AC 214 and 1480) collected June 2006 and May 2011, respectively, at the same location suggest that this is a stable colony/population that has persisted for at least 14 years. It’s probably an endophyte that kills a limited part of the branch and possibly aids in pruning.
Prosthecium stylosporum seems to be a North American species restricted to Acer spicatum.
Mycoportal – Apart from my collections from PEI only a few references are listed and most are from four collections made by Cain, Dearness, Groves and Wehmeyer, all from Ontario, Nova Scotia (Canada) or New Hampshire (United States). The report from Germany is erroneous (see below).
Pseudovalsa stylospora Ellis & Everh.
02932662A. Bagge 1251
This is not P. stylosporum but P. macrospora on Carpinus sp. (see image below from Mycoportal)
Barr, M.E. The Diaporthales of N.Am. p. 186 1978. as Prosthecium stylosporum in Barr 1978. Wehmeyer, L.E. 1941 (Reprint 1973). A revision of Melanconis, Pseudovalsa, Prosthecium and Titania. Univ. Mich. Stud. 14:1-161. As Pseudovalsa stylospora.