Ultrastructure of the ascus apical apparatus in Leotia lubrica and some Geoglossaceae (Leotiales, Ascomycotina)

The ultrastructure of the apical apparatus and lateral ascus wall is compared in Leotia lubrica and five species currently placed in the Geoglossaceae. The lateral ascus wall consists of two layers, of which the inner one increases in thickness in the apical apparatus. Considerable differences in substructure of both layers are described. On the basis of general morphology of the apical apparatus, structure and PA-TCH-SP reactivity of the apical thickening and annulus, and occurrence of an annular protrusion four main categories are distinguished. A reactive annulus is demonstrated in the apical apparatus of all species, including L. lubrica. The species studied are arranged as follows: Category 1a. Geoglossum nigritum and G. cookeianum; 1b. Trichoglossum hirsutum; 2. Leotia lubrica; 3. Microglossum viride; 4. Mitrula paludosa. Most fundamental is considered the position of the annulus in the apical thickening, either fully (category 1) or partly (2—4) occupying the apical thickening, either associated with an annular protrusion (3, 4) or not (1, 2). The data on the ultrastructure of the ascus apical apparatus and lateral wall, and mode of dehiscence indicate that L. lubrica takes an isolated position, distant from the other Leotioideae (including Ombrophiloideae) and the Geoglossaceae. Geoglossum, Trichoglossum, and Microglossum can best be maintained as separate genera in the family Geoglossaceae. The ultrastructural data of M. paludosa indicate closer affinity with Sclerotiniaceae than with Geoglossaceae.