Studies in the morphology of Discomycetes: V. The evolution of the ascocarp ( continued)

Abstract

Current views on the evolution of Ascomycetes are considered. Church's hypothesis of evolution from complex marine phytobenthos is upheld because it explains the origin of the multaxial ascocarp which the hypothesis of juvenescence postulates as the primitive form of ascocarp in Discomycetes. Conclusions drawn from phycology and mycology are in agreement and the multaxial ascocarp is homologised with a multaxial cable type of algal soma bearing numerous parasitic filamentous sporophytes. The postulate presupposes a massive autotrophic vegetation and the hypothesis of juvenescence supports Church's hypothesis of subaerial transmigration of marine phytobenthos. It is shown that in Pyrenomycetes the simple forms of ascocarp can also be interpreted as juvenile expressions of a multaxial form. It is considered that Pyrenomycete and Discomycete series converge to the limit of the cleistocarp and that the Plectascales are degenerate members of both series. A juvenescent series can be traced from the multaxial ascocarp to the condition of the yeast plant which never becomes a multicellular organism. The difficulty in recognising degenerate cleistocarpic forms of operculate and inoperculate Discomycetes, Pyrenomycetes and possibly Lichen fungi is indicated. The upgrade theory of the evolution of Discomycetes from Plectascales is considered untenable because evidence is lacking that any simple form of ascocarp belongs to a primitive Discomycete : it ignores the similarity in the factors of equipment of Discomycetes and marine phytobenthos and it lacks biological support. Likewise the exponents of the origin of Ascomycetes from Florideae fail to recognise the importance of somatic organisation and deal only with forms of ascocarp which are considered reduced and juvenile. While Ascomycetes cannot be referred to any algal series they embody to some extent the equipment of Preflorideae. The term “discopodium” is suggested for the monaxial ascocarp of Discomycetes. The state of the sporophytic system of the discopodium is briefly considered.