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.
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.
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
Ascal apical ring is flattened, usually
(bluing in Melzer's reagent), diagnostic when absent or inamyloid.
Paraphyses are always present among asci but their characters are not
Shape: varying in European taxa from rarely
ellipsoid in side view
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
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
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!