Reconsideration of relationships within the Thelebolaceae based on ascus ultrastructure

Genera that have been included in the family Thelebolaceae Eckblad are considered for the structure of the apical apparatuses of their asci. In the absence of such information, other characters could sometimes be used to clarify their most likely taxonomic position. The affinities of Cleistothelebolus, Coprobolus, Coprotiella, Dennisiopsis, Lasiobolidium, Lasiothelebolus, Leptokalpion, Mycoarctium, Ochotrichobolus, and Zukalina are discussed. The ultrastructure of ascus tops has been studied in Thelebolus microsporus, T. coemansii, T. caninus, T. crustaceus, T. polysporus, T. nanus, T. stercoreus, Caccobius minusculus, Lasiobolus pilosus, L. cuniculi, L. monascus, Ascozonus woolhopensis, A. solmslaubachii, Ramgea annulispora, Coprotus lacteus, and Trichobolus zukalii. At least six different types of asci can be distinguished within the fungi studied by electron microscopy. (1) The first (typical) Thelebolus type, in Thelebolus microsporus, T. crustaceus, T. stercoreus, Caccobius, Ramgea, and Pseudascozonus, opening after splitting within the inner wall layer in the apex, mostly accompanied by a central apical thickening. (2) The second Thelebolus type, in T. caninus and T. polysporus, with a breakdown of the inner layer in the apex above the subapical ring, followed by an irregular tear in the outer layer. (3) The third Thelebolus type, in T. microsporus and T. coemansii, with an irregular operculum just above the subapical ring. (4) The Ascozonus type, restricted to Ascozonus, with a very prominent subapical ring and a very small operculum. (5) The Trichobolus type, restricted to the uni-ascal multi-spored genera Trichobolus and Leptokalpion, without any trace of a subapical ring or weakened zone, showing a very large operculum or an irregular tear, caused by a regular retraction of the outer layer from a circular apical region. (6) The asci of Lasiobolus and Coprotus agree with the earlier defined Octospora type. New combinations were necessary for Thelebolus coemansii and Ascozonus solms-laubachii.