Xerocomellus is a genus of fungi in the family Boletaceae. The genus, as it was described in 2008, contained 12 species. However X. rubellus and X. engelii were transferred to the new genus Hortiboletus and X. armeniacus was transferred to the new genus Rheubarbariboletus in 2015. Molecular analysis supports the distinction of Xerocomellus species from Boletus and Xerocomus, within which these species were formerly contained. Xerocomellus in fact is only distantly related to Xerocomus and is most closely related to Tylopilus, Boletus sensu stricto, Porphyrellus, Strobilomyces, and Xanthoconium.
Taxonomy Members of the genus had been classified either in the genus Boletus or Xerocomus until Czech mycologist Josef Šutara examined a number of species and concluded that there was a defined group containing X. chrysenteron, X. armeniacus and relatives that are distinct morphologically from the group containing Xerocomus subtomentosus and related species. He deferred fully delimiting the genus until genetic work confirmed their distinctness. Previously, Manfred Binder had coined the term Paraxerocomus for the group but this was not officially published.
The type species is the red-cracked bolete (Xerocomellus chrysenteron).
Genetic analysis published in 2013 showed that X. chrysenteron and X. zelleri form a Xerocomellus clade within a larger group informally called "anaxoboletus" in the Boletineae. It appears to have affinities with what was then known informally as the "rubellus clade", which contained the species X. rubellus and X. armeniacus, now known as Hortiboletus rubellus and Rheubarbariboletus armeniacus respectively. The same study found Xerocomellus to be more distantly to a 'badius' clade containing Boletus badius, now known as Imleria badia, and relatives. Other clades in the group include the porcini (true Boletus species) and Strobilomyces clades, species currently designated Xerocomus (the species are not true Xerocomus species), and smaller genera whose relationships are unclear.
Description Members of the genus have small to medium-size fruit bodies with more slender stipes compared with other boletes. They are often brightly coloured. The caps are dry and do not become sticky when wet. Their cuticle tissue is a palisadoderm, comprising parallel or roughly parallel hypha arranged in an anticlinal fashion. The palisoderm, which is generally between 120 and 350 μm thick (although extremes of 80 μm and 500 μm are known), maintains its characteristic arrangement for longer periods than other boletes. The tubes are generally yellow and adnate or slightly decurrent. The pores are also yellow and quite large, up to 2.5 mm in diameter each and angular in shape. The spores are generally spindle-shaped to oval and have a smooth or striate surface. The spore print is brown or slightly olive-tinged when fresh.
Morphological Features of Xerocomoid Boletes
Boletus s.str. Hemileccinum Xerocomellus Xerocomus s.str. Spore surface Smooth Smooth Longitudinally striated or smooth, never bacilate Bacilate Hymenophoral trama Boletoid type with gelatinous lateral strata Boletoid type with gelatinous lateral strata Intermediate between boletoid and phylloporoid when fully developed with distinct but weakly gelatinous lateral strata Phylloporoid type with nongelatinous lateral strata Pileipellis Trichoderm, sometimes collapsing, rarely ixotrichoderm or other Initially trichoderm but collapses with age Initially palisadoderm, typically encrusted Initially a trichoderm, never encrusted Lateral stipe stratum Frequently gelatinous, 60–90 μm thick, thicker than that of Xerocomellus Similar to that of Leccinum species, ornamented with stipe scabrousities up to 400–640 μm thick Frequently not present, reduced to no more than 30–40 μm thick, not gelatinous Lateral stipe stratum never gelatinous and 80–200 μm thick
Ecology Xerocomellus species form mycorrhizal associations with coniferous and deciduous trees.
Species
Image Scientific name Taxon author Year Basionym DistributionX. amylosporus (A.H. Sm.) J.L. Frank & N. Siegel,2020 Porphyrellus amylosporus A.H. Sm., (1965).Vancouver Island, British Columbia, Canada, south into CaliforniaX. atropurpureus J.L. Frank, N. Siegel & C.F. Schwarz,2020British Columbia south at least to Monterey County, California along the coast, inland to the Sierra Nevada and Cascade RangeX. behrii (Harkn.) Castellano, M.E. Sm. & J.L. Frank2018 Splanchnomyces behrii Harkn., (1884).California and OregonX. bolinii J.A. Bolin, A.E. Bessette, A.R. Bessette, L.V. Kudzma, J.L. Frank & A. Farid2021FloridaX. carmeniae Garza-Ocañas, J. García & de la Fuente2022 Mexico (Nuevo León)X. chrysenteron (Bull.) Šutara2008 Boletus chrysenteron Bull. (1791)cosmopolitanX. cisalpinus (Simonini, H.Ladurner & Peintner) Klofac2011 Xerocomus cisalpinus Simonini, H. Ladurner & Peintner (2003)mainland Europe and in North America.X. communisXue T. Zhu & Zhu L. Yang2016China (Yunnan)X. corneriXue T. Zhu & Zhu L. Yang2016ChinaX. diffractusN. Siegel, C.F. Schwarz, & J.L. Frank2020central California, through the Pacific Northwest into British Columbia, Canada, east to the Rocky Mountains of Wyoming, and south into ArizonaX. dryophilus (Thiers) N. Siegel, C.F. Schwarz & J.L. Frank2014 Boletus dryophilus ThiersNorth AmericaX. fennicus (Harmaja) Šutara2008 Boletellus fennicus Harmaja (1999)Austria, Czech Republic, Denmark, Finland and Sweden, possibly also BelgiumX. fulvus Sarwar, I. Ahmad & Khalid2016 PakistanX. himalayanus D. Chakr and A. Ghosh2023 India (Himachal Pradesh)X. intermedius (A.H. Sm. & Thiers) Svetash., Simonini & Vizzini2016 Boletellus intermedius A.H.Sm. & Thiers (1971)Northeastern United StatesX. macmurphyi (Zeller & C.W. Dodge) Castellano, Saylor, M.E. Sm., & J.L. Frank2018Hymenogaster macmurphyi Zeller & C.W. Dodge, 1934.California and OregonX. marekii (Šutara & Skála) Šutara2008 Boletus marekii Šutara & Skála (2007)Czech Republic and HungaryX. mendocinensis (Thiers) N. Siegel, C.F. Schwarz & J.L. Frank2020 Boletus truncatus (Singer, Snell, & Dick) PouzarWestern United States X. perezmorenoiAyala-Vasquez & M. Martinez-Reyes2023MexicoX. poederi G. Moreno, Heykoop, Esteve-Rav., P. Alvarado & Traba 2016EuropeX. porosporus (Imler ex G.Moreno & Bon) Šutara2008 Boletus porosporus Imler ex Bon & G.Moreno (1977)EuropeX. pruinatus (Fr. & Hök) Šutara2008 Boletus pruinatus Fr. & Hök (1835)EuropeX. rainisiae(Bessette & O.K. Mill.) N. Siegel, C.F. Schwarz & J.L. Frank2014Boletus rainisiae Bessette & O.K. Mill. [as “rainisii”], in Bessette et al., 2000. Vancouver Island, British Columbia, Canada, south into Oregon.X. redeuilhii A.F.S. Taylor, U. Eberh., Simonini, Gelardi & Vizzini2016 Boletus dryophilus Simonini, (1994) Xerocomus dryophilus Ladurner & Simonini (2003) EuropeX. ripariellus (Redeuilh) Šutara2008 Xerocomus ripariellus Redeuilh (1997) EuropeX. salicicola C.F. Schwarz, N. Siegel & J.L. Frank2020 Xerocomus salicicola C.F. Schwarz, N. Siegel & J.L. Frank (2020) Western North AmericaX. sarnarii Simonini, Vizzini & Eberhardt2015 Italy, FranceX. truncatus (Singer, Snell & E.A.Dick) Klofac2011 Xerocomus truncatus Singer, Snell & E.A.Dick (1959)Eastern North AmericaX. zelleri (Murrill) Klofac 20112011 Ceriomyces zelleri Murrill (1912)Northwestern North America
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