The Lecanoralean Ascus: An Ultrastructural Preliminary Study

Abstract

The term “Lecanorales” must be precisely defined at the outset because of the diverse concepts of this group held by various authors. Nannfeldt (1932) established a broad definition of the group by uniting under the Lecanorales the asco-hymenial discomycetes which are characterized by a perennial ascocarp and an ascus in which the wall stains blue with iodine. As a result, he assigned to this taxon a small number of non-lichen-forming discomycetes, the family Patellariaceae, along with nearly all the discolichens with the exception of the Caliciaceae-like species and some of the paraphysoid graphidiate species. This is nearly the same point of view as that of Dennis (1968). As a result of the work by more recent authors including Richardson (1970), Duncan and James (1970), Luttrell (1973), Poelt (1973), Henssen and Jahns (1974) and Von Arx and Müller (1975), some families or genera have been separated out—generally on the basis of characteristics of the ascus and the ascocarp (e.g., the genera Patellaria Fries and relatives, Baeomyces Persoon and allies and the families Graphidaceae, Lecan-actidaceae, Thelotremataceae and its allies, and Gyalectaceae). These authors differ over only a small number of families. They are in general agreement on a fundamental definition of the order Lecanorales as the ascohymenial discomycetes that have asci of the archaeascé type. This corresponds to the lecanoralean discomycete concept of Chadefaud (1960) with the exclusion of the ascohymenial discomycetes having bitunicate asci.