Xerocomus Quél.
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 chrysenteron (Bull.) Quél.
Description
Cap up to 10 cm, at first hemispherical, later convex to flattened, ochraceous, greysh ochraceous, light to dark brown, greyish brown, or olivaceous brown, dry, at first velvety, but very soon cracking and pinkish flesh is seen in the cracks. Stipe cylindrical, in the upper part yellowish or yellow, downwards gradually becoming red, covered with fine red granules, often discolouring with age, blueing when bruised. Tubes pale yellow to yellow with olivaceous tint, blueing when injured. Pores concolorous with the tubes, blueing when bruised. Flesh whitish to yellowish in the cap, yellow in the stipe, in the lower parts of the stipe often carmine to vinaceous red, blueing slightly when exposed to air. Smell not distinctive. Taste not distinctive. Spores 11–17 × 4–6.5 μm, smooth. Pileipellis palisadoderm of septate hyphae of cylindrical, incrusted cells.
Habitat. Broadleaf, mixed or coniferous forests, mycorrhizal mostly with spruce (Picea) or rarely with beech (Fagus) and showing preference to areas with cold to moderate climate.
Distribution. In Europe widespread, but the true distribution is yet to be justified as it might have been confused in the past with Xerocomus cisalpinus, X. communis and X. pruinatus.
Similarity. Xerocomus chrysenteron is similar to a number of species, namely:
Xerocomus communis and discoloured forms of X. rubellus – both easily recognized due to the presence of red dots in the flesh in the stipe base;
Xerocomus cisalpinus, which has striate spores and grows mostly in warm broadleaf woodlands;
Xerocomus pruinatus, which has not cracking cap cuticle, striate spores and slowly bluieng flesh.
Fruitbodies of Xerocomus chrysenteron. (photo B. Assyov)
Typical fruitbodies of Xerocomus chrysenteron. (photo B. Assyov)
Typical fruitbodies of Xerocomus chrysenteron. (photo I. Assyova)
Fruitbodies of Xerocomus chrysenteron with deeply cracked cap surface. (photo B. Assyov)
Xerocomus chrysenteron - cap surface. Note the pinkish tint of the flesh in the cracks. (photo B. Assyov)
Xerocomus chrysenteron - colours of the flesh. The reddish tint is often seen in the stipe base, but the lack of blueing is unusual. (photo B. Assyov)
Important literature
Engel, H., Dermek, A., Klofac, W., Ludwig, E. & Brückner, T. 1996. Schmier – und Filzröhrlinge s. l. in Europa. Die Gattungen Boletellus, Boletinus, Phylloporus, Suillus, Xerocomus. Verlag Heinz Engel, Weidhausen b. Coburg.
Hills, A.E. 2008. The genus Xerocomus. A personal view, with a key to the British species. Field Mycology 9(3): 77–96.
Knudsen, H. & Vesterholt, J. [eds.]. 2008. Funga Nordica. Nordsvamp, Kopenhagen.
Ladurner, H. & Simonini, G. 2003. Xerocomus s.l. – In: Fungi Europaei. Vol. 8. Pp. 1–527. Edizioni Candusso, Alassio.
Simonini, G. 1998. Xerocomus chrysenteron e X. rubellus: delimitazione e casi di simulazione. – Micologia e Vegetazione Mediterranea 13: 69–89.
Šutara, J., Mikšík, M. & Janda, V. 2009. Hřibovité houby. Čeled’ Boletaceae a rody Gyrodon, Gyroporus, Boletinus a Suillus. Academia, Praha.
Watling, R. & Hills, A.E. 2005. Boletes and their allies (revised and enlarged edition). – In: Henderson, D.M., Orton, P.D. & Watling, R. [eds]. British Fungus Flora. Agarics and boleti. Vol. 1. Royal Botanic Garden, Edinburgh.