Genus Hypoxylon
Key to Taxa of Hypoxylon
Accepted Taxa
List of Names

Yu-Ming Ju
Michael J. Adams

Ostioles have weighed heavily in the taxonomy at subgeneric levels. Miller (1961) classified taxa with "umbilicate" ostioles in section Hypoxylon, taxa with "papillate" ostioles in section Papillata, and taxa with discs surrounding ostioles in section Annulata. However, it should be emphasized that every taxon that we have studied essentially has papillate ostioles. In section Hypoxylon, the umbilicate feature in most taxa is actually caused by loss of stromatal tissue directly above the papillate ostioles which come to be lower than the stromatal surface (Figs. 1A, 1B, & 1C). Therefore, we prefer to describe ostioles as being higher or lower than the stromatal surface instead of being "umbilicate" or "papillate". Levels of ostioles relative to stromatal surfaces are useful in determining whether a fungus belongs to section Hypoxylon or section Annulata. Only a few taxa in section Hypoxylon have ostioles higher than the stromatal surface, but virtually every member of section Annulata has ostioles higher than the stromatal surface. The ostiolar disc is one of the hallmarks of section Annulata (Figs. 1F-1I and also see truncatum-type and bovei-type ostiolar disc formations); it is found exclusively in this section.

Figure 1. A-I. Vertical sections of stromata in various Hypoxylon showing the distributions of different stromatal tissues. A. H. rubiginosum. B. H. fragiforme. C. H. placentiforme. D. H. monticulosum. E. H. multiforme. F. H. annulatum. G. H. stygium. H. H. nitens. I. H. bovei. a: outermost stromatal layer; b: waxy stromatal tissue; c: woody stromatal tissue; d: carbonaceous stromatal tissue; p: perithecial wall.

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