ULTRASTRUCTURE OF THE ASCUS IN THE GENERA LACHNUM AND TRICHOPEZIZA (HYALOSCYPHACEAE, ASCOMYCOTINA)

The ultrastructure of the ascus apical apparatus, lateral ascus wall, and ascospore wall was compared in two species of Hyaloscyphaceae (Leo tiales), Lachnum virgineum and Trichopeziza mollissima. These species agree in general morphology of the apical apparatus. The well-develope d and persistent annular protrusion surrounds an apical chamber. After dehiscence the apical thickening is everted over about a right angle. The species differ in respect of PA-TCH-SP reactivity of the annulus, outer layer erosion, periascus, and extent of the apical thickening, which supports their current position in separate genera. In both spec ies secondary ascospore wall differentiation is preceded by a lifting of the investing membrane from the surface of the primary wall. Second ary wall structure also agrees, with a strongly PA-TCH-SP reactive, sm ooth epispore covering an undifferentiated endospore. The structure of the apical apparatus in L. virgineum and T. mollissima agrees with th at in Calycina and species of Pezizella. The recent transfer of these taxa from the Leotiaceae to the Hyaloscyphaceae after revision of main ly excipular characters is now consolidated by ultrastructural data of the ascus.