TAMSINIELLA LABIOSA GEN. ET SP.NOV., A NEW FRESH-WATER ASCOMYCETE FROM SUBMERGED WOOD

Investigations into the fungi occurring on wood submerged in freshwate r ecosystems have revealed a unique, but characteristic group of fungi . In this paper a new pyrenomycete, Tamsiniella labiosa gen. et sp.nov ., is described and illustrated with light, scanning, and transmission electron micrographs. The genus has remarkable short stipitate cylind rical asci with an internal refractive apical ring that are apically t runcate and have an external thickening. Ascospores are ellipsoidal-fu siform and surrounded by a mucilaginous sheath. At the transmission el ectron microscope level, the annulus part of the ascus apical apparatu s is differentiated from the inner ascus wall layer and is composed of horizontally oriented, electron-dense fibrillar material. A narrow pl ug is present in the centre of the apical ring. An electron-dense amor phous region occurs between the outer ascus wall layer and the annulus part of the apical apparatus. The outer ascus wall layer is lacking a t the apex. The ultrastructure of the ascus apex differs from those de scribed in the Lasiosphaeriaceae, Sordariaceae, and Xylariaceae.