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Page number:667 
Remarks (public):H. quercina has a variable morphology and has therefore very often been incorrectly interpreted. This is true especially in young specimens, in which the aculei are still small (less than 1 mm). Such specimens are very similar to H. crustosa. Under the microscope it is better distinguished, because of its larger basidia and spores and because of the lack or very low frequency of subulate cystidiols. It seems to belong to the H. crustosa-group, even if we have not been able to settle the presence of internal, linear repetition. This problem will best be solved when living material is studied. In the herbarium material the mature aculei are tough and therefore difficult to prepare.
Authentical Friesian material has not been seen. Specimens of H. fallax Fr. and H. paradoxum Fr. in Fries's herbarium (U) seem to (belong here.
 
Description type:Non-original description 
Description:Hyphodontia quercina (Fr.) John Erikss., Symb. bot. Ups. 16:1 p. 105, 1958. - Hydnum quercinum Fr., Syst. mycol. I p. 423, 1821.
Fruitbody resupinate, usually orbicular at first, then confluent and effuse, adnate, ceraceous when wet and alive, fibrous and rather tough when dried, whitish at first, then cream-coloured and at last ochraceous; hymenophore odontioid or almost raduloid, aculei variable, conical to subcylindrical, ab. 2-3 mm long in mature specimens but often smaller, apically more or less fimbriate under the lens; subiculum in dried specimens often more or less cracked; margin variable, indeterminate and pruinose in young specimens, more determinate in mature ones, sometimes with a narrow, fibrillose sterile zone.
Hyphal system monomitic; hyphae ab. 2-3 µm in diam., distinct, fibulate, thickened in the subiculum, parallelly arranged in the centre of the aculei, irregularly intertwined in the subiculum, in the subhymenium densely and the predominant hyphal direction perpendicular to the hymenial surface; sterile hyphal ends in the hymenium mostly capitate with apical encrustation, in the aculeal apices obtuse or tapering to almost subulate; globose swellings on the hyphae of the aculeal trama often present; younger hyphae cyanophilous.
Cystidia none; capitate sterile hyphal ends in the hymenium, varying in number, from rather frequent to very few; in some specimens also a few subulate cystidiols are observed.
Basidia subclavate at first, then subcylindrical with suburniform constriction, basally tapering, mostly 25-35 x 4,5-5,5 µm, in young hymenia sometimes longer, thinwalled or basally with slightly thickened walls, normally 4 sterigmata, several oildrops in the protoplasm, basal clamp.
Spores cylindrical, adaxial side somewhat concave, smooth, thinwalled, 1- or pluriguttulate, 6-7,5 x 2,5-3 µm.
Habitat. On decayed corticate or decorticate wood of deciduous trees, mostly on fallen branches or on dead but still attached ones. It is usually found only in richer biotopes, such as deciduous forest on mould soil. It is not restricted to Quercus but is collected on all sorts of deciduous trees, such as Fagus, Betula, Corylus, Alnus, Populus, Malus and Ulmus.
Distribution. Fairly common in S. Scandinavia, throughout Denmark, in Sweden north to Uppland, in Norway scattered in SE parts and the inner parts of Rogaland and Hordaland, probably not rare in SW. Finland. Unexpectedly A Strid found it in C. Lapland and another northern collection was made in NW. HÀ£lsingland by M. Ostman. B. & J. Eriksson collected it several times on Alnus rubra in Br. Colombia, Canada.
 
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