Ultrastructural observations on Helvellaceae (Pezizales, Ascomycetes). IV. Ascospore ontogeny in selected species of Gyromitra subgenus Discina

Abstract

The ultrastructure of ascospore ontogeny and spore wall microchemistry are described in three sessile, discoid species of Gyromitra previously placed in Discina. Silver proteinate and barium permanganate were used as poststains to enhance the definition of various wall layers and spore organelles. Early stages of ascosporogenesis and primary wall formation are similar to those described in other species of Pezizales. Secondary wall formation, which results in characteristic spore ornamentation, is similar in Gyromitra brunnea, Gyromitra leucoxantha, and Gyromitra perlata. Mature spores of these species differ in the size and shape of translucent lacunae within the secondary wall, and in the morphology of apiculi. The lacunae originate through blebbing of primary wall material through the epispore into the secondary wall, resulting in the isolation of electron-translucent primary wall clumps within the electron-dense secondary wall. These and other ultrastructural observations of apothecial tissues support the maintenance of the Helvellaceae (sensu lato) to include taxa of the tribes Helvelleae, Discineae, and Rhizineae. Phylogenetic linkages of these taxa to other families of Pezizales are suggested. Key words: ascosporogenesis, ascospore wall structure and microchemistry, discomycete systematics and phylogeny.