Recent molecular studies have shown that Xerocomus in its current circumscription is likely an artificial grouping and it is possible that it will be split at some point into smaller genera. Molecular studies also have changed our understanding about the species of xerocomoid boletes showing that morphological features are quite variable in this group. Not only microscopic study is essential for determination, but scanning electron microscope will be often needed in this “genus” as the spore ornamentation is not always seen under ordinary light microscope. Do bear in mind that macroscopic characters, such as colours, cracking cuticle, etc., tend to intergrade between the different species. Note that Boletus impolitus and Boletus depilatus that were shown to be close to Xerocomus subtomentosus and its allies, are here retained in Boletus for practical reasons. The same applies also for Phylloporus pelletieri, placed here in a genus of its own, but being also close to Xerocomus subtomentosus group.
Although large reference list will be found under most of the species, one should always consult Ladurner & Simonini (2003) having in mind that there are some new species (X. chrysonemus, X. marekii, X. silwoodensis) described after this otherwise superior book was printed. Useful keys, covering most of the European xerocomoid boletes (except some southern taxa) are provided by Knudsen & Vesterholt (2008), Hills (2008) and Kibby (2011), the later also featuring an excellent comparison chart.
Fruitbody medium to small sized, boletoid, without veil and ring. Stipe solid, often tapering towards the base. Flesh variously coloured, changing or not when exposed to air. Tubes not separable from each other, instead tearing apart. Pores usually angular.
Xerocomus badius (Fr.: Fr.) E.-J. Gilbert
Cap up to 15 cm, at first hemispherical, later convex to flattened, dark reddish brown, chestnut brown to dark brick coloured, smooth when dry, but distinctly viscid in wet weather. Stipe cylindrical, spindle-shaped or almost club-shaped, often tapered towards the base, concolorous with the cap or slightly paler. Tubes cream to pale yellow, blueing or not blueing when injured. Pores concolorous with the tubes, blueing when bruised. Flesh whitish or yellowish, blueing in the cap when exposed to air. Smell not distinctive. Taste not distinctive. Spores 11–15 × 4–6 μm, smooth. Pileipellis trichoderm of septate hyphae of cylindrical, smooth or incrusted cells.
Habitat. Mainly in coniferous or mixed forests, mycorrhizal mostly with spruce (Picea) or pines (Pinus), but also rarely with beech (Fagus) or oaks (Quercus).
Distribution. In Europe widespread and common.
Similarity. Usually easily distinguished, Xerocomus badius may sometimes slightly resemble Xerocomus moravicus, but the later has white flesh that is not blueing, unchanging yellow pores and grows in different habitat.
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