ULTRASTRUCTURE OF THE ASCUS APICAL APPARATUS IN HYMENOSCYPHUS AND OTHER GENERA OF THE HYMENOSCYPHOIDEAE (LEOTIALES, ASCOMYCOTINA)

The ultrastructure of the ascus apical apparatus is compared in 19 spe cies of the Hymenoscyphoideae, currently placed in seven genera. The a scus wall consists of an outer layer of two strata, and an inner layer of also two, and in one species of three strata. At the apex only the inner layer increases in thickness. On the basis of the general morph ology and PA-TCH-SP reactivity pattern of the apex five main groups ar e recognized. A further division into subgroups is also outlined. The most important diagnostic features used in the analysis are the relati ve development and the reactivity pattern of the apical thickening, th e occurrence of an annular protrusion, the structure and the reactivit y pattern of the annulus, and the apex maturation pattern. In addition to the electron micrographs diagrammatic schemes are given to illustr ate the author's interpretation. The species studied are thus arranged as follows: Group la. Hymenoscyphus caudatus, H. fructigenus, H. sali cellus, H. salicinus, and Bisporella pallescens; 1b. H. imberbis and P haeohelotium subcarneum; 1c. H. consobrinus, H. repandus, and Crocicre as pallidum; 1d. Discinella boudieri; Group 2a. H. herbarum; 2b. Peziz ella gemmarum; 2c. Chlorociboria aeruginascens and Pezizella alniella; 2d. Crocicreas cyathoideum [var. cyathoideum]; Group 3. Bisporella su lfurina; Group 4. Cudoniella clavus var. grandis; Group 5. Cudoniella acicularis. Most fundamental are considered firstly the position of th e annulus in the apical thickening, either partly (groups 1, 2, 4, 5) or fully (3) occupying the thickening, either associated (2, 4, 5) or not associated with an annular protrusion (1), and secondly the dehisc ence mechanism, either an eversion of the annulus over an angle of abo ut 90 degrees (1, 2, 3?, 4) or a two-step mechanism (5) previously und escribed in Leotiales. The absence of an amyloid reaction in the apex, which is a diagnostic feature in Cudoniella acicularis and C. clavus var. grandis, is based on two fundamentally different structures in th ese species. The apex in the last mentioned fungus closely resembles t hat in Ombrophila violacea, while the apex in C. acicularis is unique in general morphology and dehiscence mechanism. The ultrastructural da ta of the apical apparatus are found to correlate with characters of e xcipulum anatomy, especially in the genera Hymenoscyphus and Bisporell a. Their importance in segregating more natural genera from large ill- defined genera like Hymenoscyphus or Pezizella is discussed.