Emendations to tissue typology in discomycetes

Abstract

AbstractThe term “textura oblita”, referring to a tissue type in ascomycetes with apothecial ascomata, has caused much confusion to ascomycologists. Originally it was defined as a long-celled tissue type consisting of thick-walled hyphae with intercellular substance. However, this definition appeared not well, or not at all, applicable to the originally given examples like Phialea starbaeckii. This has resulted in two other definitions which are more or less the opposite of each other, viz. as a thick-walled tissue with gelatinized walls and as a thin-walled tissue embedded in a gelatinous matrix. The main issue is the location of the gelatinous substance in the relevant tissue: in the cell wall, extracellular, or both. Unfortunately all of the three tissues are called “gelatinous tissue”, although the term “gelatinous tissue” according to its definition concerns only tissue with extrahyphal gel. This implies that essential information about the location of the gel is ignored. In effect, all three conceptions of textura oblita are reducible to versions of textura porrecta that differ in the location of the gel. Similarly other tissue types can occur in different versions.The author discusses the postulated mechanisms of gel formation in fungal tissues. These concern disintegration of the outer layer(s) of hyphal walls, disintegration of hyphae, and secretion, here linked to exocytosis. There is supposed to be a correlation between the way of gel formation on the one hand, and the structure of the sporocarp and the cell wall in ascomycetes and basidiomycetes on the other hand.To conclude, an emended tissue typology is provided in which the distinguished versions of the six basic tissue types are arranged according to the shape of their cells, the arrangement of their hyphae, the occurrence of thickened cell walls, and the occurrence of extracellular gel.The species name Cyathicula starbaeckii, comb. nov., is validly published here.