Xerocomellus

Xerocomellus is a genus of fungi in the family Boletaceae. The genus, as it was described in 2008, contained 12 species.[1] 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.[2][3] 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.[4]

Xerocomellus
Xerocomellus chrysenteron
Scientific classification
Kingdom:
Fungi
Division:
Basidiomycota
Class:
Agaricomycetes
Order:
Boletales
Family:
Boletaceae
Genus:
Xerocomellus

Šutara (2008)
Type species
Xerocomellus chrysenteron
(Bull.) Šutara (2008)
Species

see text

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.[1] Previously, Manfred Binder had coined the term Paraxerocomus for the group but this was not officially published.[1]

The type species is the red-cracked bolete (Xerocomellus chrysenteron).[1]

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.[2] The same study found Xerocomellus to be more distantly to a 'badius' clade containing Boletus badius, now known as Imleria badia, and relatives.[5] 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.[4]

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.[1] 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.[1]

Morphological Features of Xerocomoid Boletes[1][6][7]

Boletus s.str.HemileccinumXerocomellusXerocomus s.str.
Spore surfaceSmoothSmoothLongitudinally striated or smooth, never bacilateBacilate
Hymenophoral tramaBoletoid type with gelatinous lateral strataBoletoid type with gelatinous lateral strataIntermediate between boletoid and phylloporoid when fully developed with distinct but weakly gelatinous lateral strataPhylloporoid type with nongelatinous lateral strata
PileipellisTrichoderm, sometimes collapsing, rarely ixotrichoderm or otherInitially trichoderm but collapses with ageInitially palisadoderm, typically encrustedInitially a trichoderm, never encrusted
Lateral stipe stratumFrequently gelatinous, 60–90 μm thick, thicker than that of XerocomellusSimilar to that of Leccinum species, ornamented with stipe scabrousities up to 400–640 μm thickFrequently not present, reduced to no more than 30–40 μm thick, not gelatinousLateral stipe stratum never gelatinous and 80–200 μm thick

Ecology

Xerocomellus species form mycorrhizal associations with coniferous and deciduous trees.[1]

Species
ImageScientific NameTaxon authorYearBasionymDistribution
X. chrysenteron (Bull.) ŠŠutara 2008 Boletus chrysenteron Bull. (1791)[8] Taiwan
X. cisalpinus (Simonini, H.Ladurner & Peintner) Klofac[9] 2011 Xerocomus cisalpinus Simonini, H. Ladurner & Peintner (2003)[10] mainland Europe and in North America.
X. dryophilus (Thiers) N. Siegel, C.F. Schwarz & J.L. Frank 2014 Boletus dryophilus Thiers North America.
X. fennicus (Harmaja) ŠŠutara 2008 Boletellus fennicus Harmaja (1999)[11] Austria, Czech Republic, Denmark, Finland and Sweden, possibly also Belgium
X. marekii (ŠŠutara & Skála) ŠŠutara 2008 Boletus marekii Šutara & Skála (2007)[12] Czech Republic and Hungary
X. porosporus (Imler ex G.Moreno & Bon) ŠŠutara 2008 Boletus porosporus Imler ex Bon & G.Moreno (1977)[13] Europe
X. pruinatus (Fr. & Hök) ŠŠutara 2008 Boletus pruinatus Fr. & Hök (1835)[14] Europe
X. ripariellus (Redeuilh) ŠŠutara 2008 Xerocomus ripariellus Redeuilh (1997)[15] Europe
X. salicicola C.F. Schwarz, N. Siegel & J.L. Frank 2020 Xerocomus salicicola C.F. Schwarz, N. Siegel & J.L. Frank (2020)[16] Western North America
X. truncatus (Singer, Snell & E.A.Dick) Klofac[9] 2011 Xerocomus truncatus Singer, Snell & E.A.Dick (1959)[17] Eastern North America
X. zelleri (Murrill) Klofac 2011[9] 2011 Ceriomyces zelleri Murrill (1912)[18] Northwestern North America

References
  1. Šutara J. (2008). "Xerocomus s. l. in the light of the present state of knowledge" (PDF). Czech Mycology. 60 (1): 29–62.
  2. Vizzini A. (26 June 2015). "Nomenclatural novelties" (PDF). Index Fungorum: 1. ISSN 2049-2375.
  3. Biketova, Alona Yu. (2 September 2015). "Nomenclatural novelties" (PDF). Index Fungorum (257): 1. ISSN 2049-2375.
  4. Nuhn ME, Binder M, Taylor AF, Halling RE, Hibbett DS (2013). "Phylogenetic overview of the Boletineae". Fungal Biology. 117 (7–8): 479–511. doi:10.1016/j.funbio.2013.04.008. PMID 23931115.
  5. Vizzini A. (12 June 2014). "Nomenclatural novelties" (PDF). Index Fungorum (147): 1. ISSN 2049-2375.
  6. Šutara, J. (1989). "The delimitation of the genus Leccinum". Ceská Mykologie. 43: 1–12.
  7. Šutara J. (1991). "Pseudoboletus, a new genus of Boletales". Ceská Mykologie. 45 (1–2): 1–9.
  8. Bulliard JBF. (1791). Herbier de la France (in French). 11. plate 490.3.
  9. Klofac W. "Rotfußröhrlinge (Gattung Xerocomellus) in aktueller Sicht". Österreichische Zeitschrift für Pilzkunde (in German). 20: 35–43.
  10. Peintner U, Ladurner H, Simonini G (2003). "Xerocomus cisalpinus sp. nov., and the delimitation of species in the X. chrysenteron complex based on morphology and rDNA-LSU sequences". Mycological Research. 107 (6): 659–79. doi:10.1017/S0953756203007901. PMID 12951793.
  11. Harmaja H. (1999). "Boletellus fennicus, a new species from Finland". Karstenia. 39: 37–8.
  12. Šutara J, Skála E (2007). "Boletus marekii, a new species with truncate spores from the Boletus chrysenteron group" (PDF). Czech Mycology. 59 (1): 11–24.
  13. Moreno G. (1977). "Nouveaux taxons de la famille Boletaceae Chev. trouvés en Espagne". Documents Mycologiques (in French). 7: 27–8.
  14. Fries EM, Hök CT. Boleti, fungorum generis, illustratio (in Latin). Uppsala. p. 9.
  15. Redeuilh G. (1997). "Xerocomus ripariellus Redeuilh". Documents Mycologiques. 26 (104): 30–1.
  16. "Xerocomellus (Boletaceae) in western North America: Ingenta Connect". Home. Retrieved 2021-01-29.
  17. Snell WH, Singer R, Dick EA (1959). "Notes on boletes. XI". Mycologia. 51 (4): 564–77. doi:10.2307/3756143.
  18. Murrill WA. (1912). "Polyporaceae and Boletaceae of the Pacific Coast". Mycologia. 4 (2): 91–100. doi:10.2307/3753546.
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