Ultrastructure of the ascus and the ascospore wall in Scutellinia (Pezizales, Ascomycotina)

The development of wall layers in the ascus top and of ornamentation of ascospores is studied with the electron microscope in Scutellinia pseudolrechispora, S. umbrorum, S. patagonica, S. trechispora, and S. scutellata. In all species studied the ascus top shows a roughly delimited operculum and ascostome, a subapical ring, and special plasmatic structures just beneath the operculum. Details of these structures, as found with different methods of fixation and contrasting, are summarized. The structure and dehiscence mechanism of the ascus as described here for Scutellinia are considered to be characteristic of the family Pyronemataceae. The developmental pattern of the ascospore wall in S. pseudotrechispora is different from that found in the other species. The secondary wall in this species develops a complex structure not known from other representatives of the Pyronemataceae.