Hypoxylon morphological characters


Description and illustration of characters
For a detailed analysis of characters used for identifying taxa of Hypoxylon, the reader is referred to Ju & Rogers (1996). Nevertheless, we give an illustrated list of the main characters used in this work, with some comments, and a model of diagnosis sheet following Ju & Rogers (1996) that should be completed before using the keys.


Shape: effused, effused-pulvinate, pulvinate, peltate, discoid, hemispherical.

Stromatal shape is usually diagnostic when peltate, discoid or hemispherical, but when varying from effused to pulvinate the shape is often in relation with the substrate: a same species is usually effused on decorticated wood and pulvinate when growing on bark. A vertical section of a pulvinate stroma shows it is erumpent through lenticels or cracks in cortical periderm.


Shape: spherical, obovoid, tubular.

When the perithecia are immersed, the perithecial mounds are inconspicuous and the stromatal surface is even. When the perithecial mounds are conspicuous, the stromatal surface is bumpy.


Opening lower than (umbilicate), higher than (papillate), at the same level as the stromatal surface, with a disc, surrounded with a ring of white substance.

This ring, composed of white granules, appears around the ostiole in most of mature Hypoxylon taxa and therefore is usually not diagnostic, except in H. perforatum where it is conspicuous and constantly observed.


Asci are 8-spored, their shape is usually cylindrical to fusiform, in relation with the arrangement of ascospores within the ascus, their dimensions vary in relation with the size of ascospores, the length of the stipe is variable and usually not diagnostic, except in H. perforatum and perhaps in a form of H. rubiginosum.

Ascal apical ring is flattened, usually amyloid (bluing in Melzer's reagent), diagnostic when absent or inamyloid.

Paraphyses are always present among asci but their characters are not diagnostic.


Shape: varying in European taxa from rarely ellipsoid in side view to frequently ellipsoid-inequilateral.

Germ slit is visible in front view, generally on the more convex side, it may be conspicuous or not, spore-length to shorter than spore-length, straight, oblique or sigmoid, rarely at the centre of a dark band.

Perispore may be dehiscent or indehiscent in 10% KOH. When dehiscent, the perispore is easily removed from the ascospore, thus the perithecial contents must be placed very carefully in a drop of KOH, avoiding stirring the mount when placing the cover slip.


Anamorphic data given in this work rely on observation of natural anamorph found growing either on or around young stromata or on old stromata, where ascospores remaining in old perithecia can germinate and produce tufts of anamorphic tissue through the ostioles.

This method is convenient for the amateur, but needs a confirmation of the relationship between the presumed anamorph and the teleomorph by incubation of the specimen with its substrate in suitable conditions over several months until stromata become mature. Young stomata associated with the natural anamorph are often found along with mature or overmature stromata but one must be aware that different species of Hypoxylon may coexist on a same log!