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Page number:96 
Remarks (public):Discussion. An important character for the generic delimitation is the hymenial construction and the branching of the subhymenial hyphae. As in most species of Corticiaseae the hymenium in Athelia consists of separate bunches of basidia in which new basidia successively are developed from the sub-basidial cells. Athelia is characterized in.that only a few (3-4) basidial generations are developed, resulting in a thin pellicular hymenium. In most corticioid species the basidial development continues for some time and the hymenium becomes thicker and membranaceous, finally more or less fleshy.
Jülich (1972) has in his monograph adapted to a somewhat more restricted concept than earlier authors. The most important generic characters are still the pellicular fruitbodies and the non-amyloid spores. Jülich has further emphasized the form of the basidia which should be short and club-like in contrast to the longer and narrower ones in his new genera Leptosporomyces and Ceraceomyces. While the basidial generations are very few in Athelia, they are more numerous in the very closely related Fibulomyces. In this genus the sub-basidial branches are more abundant and with age interwoven or intertangled with each other. This aspect can consequently be studied only in older fruitbodies.
Athelia has hyaline hyphae even in the basal layer, this is in contrast to Confertobasidium which has brownish basal hyphae in the bottom layer of the pellicular fruitbodies.
Taxonomic remarks
The loose consistency and the negligible increase in thickness make microscopic preparations very easy to make and the appropriate characters are easy to demonstrate and measure. Nevertheless the genus has, for a long time, been in a confused state, mainly because of difficulties in the evaluations of the few available characters. In many herbaria most collections have therefore been filed under the name A. epiphylla or previously as "Corticum centrifugum".
Most species in Athelia have been separated on the basis of the number of sterigmata and of the size and shape of the spores. Another character of particular interest is the occurrence of clamps at the septa. The most commonly held opinion has been that the occurrence of clamps in Athelia is
a variable character and consequently of restricted value. However, experience from other genera in the Corticiaceae indicates that clamps at the base of the basidia generally is a very important and constant character while the frequency of clamps at the basal hyphae is more variable. E.g. in Phanerochaete and Coniophora clamps are always missing at the base of the basidia, while rare clamps occur on the basal hyphae. Jülich has demonstrated that absence or presence of basidial clamps in constant and reliable. He has further emphasized the shape of the sub-basidial cells and the spores. Concerning the latter he adopts a more restricted species concept than earlier mycologists. After careful consideration of his text and microscopic examination of the Swedish material, partly used for his revision, we find it difficult in practical work in all cases to accept this species ooncept. Consequently, we find it convenient to give A. epiphylla a wider interpretation than Jülich, and place A. alnicola, A. macrospora, A. nivea, A. ovata and A. tenuispora in A. epiphylla as subordinate taxa. A few more collections of A. arachnoidea var. sibirica have on the other hand indicated that this taxon should be raised to specific level. Further A. subsphaerospora Jül. fined. is considered to be a species of its own, and so is a collection previously placed in A. pyriforme.
Cytological remarks. Nuclei can as a rule be made visible in herbarium specimens of Athelia in the following way. A small piece of hymenium is placed in a drop of acetocarmine and covered with a cover slip. After short heating over a flame, a new drop is added at the margin of the slip. The preparation is then crushed by light tapping on the slip and is then studied in phase contrast microscope. The visibility of the nuclei varies from species to species but also from collection to collection. The state
of the specimen and the circumstances under which it is dried seem to play a role. It is interesting to observe that in the species A. pyriformis, which seems to differ from the other species of the genus, the nuclei cannot be made visible with this method. All other species treated here appear to have dikaryotic hyphae and basidiols and after meiosis 4 nuclei in the basidia. This is the case also in species lacking clamps at the base of the basidia. Some species have normally only two sterigmata. In such cases 2 nuclei enter each spore and the spores are thus binucleate. In the new species A. binucleospora there are two nuclei also when there are 4 sterigmata. The direction of the meiotic divisions in the basidium seems to vary and the basidia of Athelia are not decidedly stichic nor chiastic, but often something between. A character, which may be of interest for the circumscription of the genus, is the granular protoplasm of the young basidia, easily visible both in ordinary light microscope and in phase contrast. The granularity is best seen in KOH and Melzer.
Description type:Non-original description 
Description:Athelia Pers. emend Donk - Mycol. Europ. 1: 83, 1822, Fungus 27: 1957. Monograph: Jülich, Willd. Beih. 7, 1972.
Fruitbody thin, pellicular, white to whitish (when living often bluish white), easily separable from the substrate because of badly developed subiculum of cobwebby consistency, hymenial surface smooth when dry, often slightly wrinkled (Merulius-like) when fresh. Hyphae with or without clamps, the basal hyphae often somewhat wider and with more thickened walls than the basidia-bearing hyphae, in both cases often encrusted, rhizomorphs absent. Basidia relatively short, more or less clublike with 2-4 sterigmata. Spores smooth, non-amyloid, rounded, ellipsoid or cylindrical.
Genotypus: Athelia epiphylla Pers.
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