Slippery jack Suillus luteus, copyright Lukas Large.

Belongs within: Boletales.

The origins of a closed bolete
Published 22 June 2019

Boletes are a distinctive group of mushrooms in which the underside of the fruiting body is covered by tubular pores instead of gills. Though boletes are classified in the fungal order Boletales, not all members of this order produce bolete-type fruiting bodies (as exemplified in an earlier post). Consider, for example, the case of Gastrosuillus.

‘Gastrosuillus’ sp., copyright Danny Miller.

Gastrosuillus was recognised in 1989 for a small group of species found in North America that closely resembled members of the more typical bolete genus Suillus (the slippery jacks) except for their production of secotioid fruiting bodies, in which the pores are distorted and do not form a flattened plane, and may remain covered by an external membrane (secotioid fruiting bodies may be considered an intermediate form between typical mushrooms and the gastroid fruiting bodies of fungi such as puffballs). All Gastrosuillus species were extremely rare, known only from single locations or even single collections. Gastrosuillus suilloides and G. amaranthii were found in California, G. imbellus in Oregon, and G. laricinus in New York State. All four were found on the ground in conifer forest; fruiting bodies of G. suilloides could be buried (Bessette et al. 2000).

From its inception, a close relationship with and possibly even derivation from members of the genus Suillus seems to have been on the cards for Gastrosuillus. It should be noted that Suillus was not the only bolete genus with a secotioid satellite: as Gastrosuillus was to Suillus, so Gastroboletus was to Boletus, and Gastroleccinum was to Leccinum. So it should have come as little surprise when a molecular analysis of Gastrosuillus species by Kretzer & Bruns (1997) found them to be nested within Suillus, nor forming a single clade within that genus. Instead, the western species were well separated from the New York G. laricinus. As a result, Kretzer & Bruns advocated the synonymisation of the two genera.

Typical form of larch bolete Suillus grevillei, copyright Luridiformis.

But the demotions didn’t stop there. Not only was Gastrosuillus laricinus nested molecularly within Suillus, it appeared to be nested within a particular species, S. grevillei (conversely, the California species form a distinct lineage that is, so far as we know, entirely secotioid; the Oregon G. imbellus has not been examined molecularly owing to difficulties in extracting DNA from the single known specimen). The sole known location for G. laricinus lies within the range of S. grevillei, with the two species having been found in close proximity, and the indications were that G. laricinus was a very recent derivative of S. grevillei or possibly even a mere growth variant. Again, this is not entirely without precedent. Secotioid variants have been recorded of other mushroom species, and secotioid-like forms of the agaricoid mushroom Lentinus tigrinus have even been shown to be the result of a recessive allele of a single gene. Kretzer & Bruns (1997) therefore suggested that G. laricinus be synonymised entirely with S. grevillei. This action does not appear to have gained universal acceptance (for instance, the two are provisionally treated as distinct by Bessette et al., 2000) but is certainly worthy of consideration.

Systematics of Suillineae
| |--Brauniellula Sm. & Singer 1959KC01
| |--Fevansia Trappe & Castellano 2000KC01
| `--Rhizopogon Fr. & Nordholm 1817BB02, KC01 (see below for synonymy)
| | i. s.: R. succosus [incl. R. superiorensis]NU03
| |--+--R. evadensKB03
| | `--+--R. fuscorubensKB03
| | `--+--R. occidentalisKB03
| | `--R. ochraceorubensKB03
| `--+--R. olivaceotinctusKB03
| `--+--+--R. vulgarisKB03
| | `--+--R. burlinghamiiKB03
| | `--R. roseolusKB03
| `--+--+--R. arctostaphyliKB03
| | `--R. salebrosusKB03
| `--+--R. ellenaeKB03
| `--R. subcaerulescensKB03
| |--Cystogomphus Singer 1942KC01
| |--Gomphogaster Mill. 1973KC01
| |--Chroogomphus (Singer) Mill. 1964KC01
| | `--C. vinicolorRG97
| `--Gomphidius Fr. 1836BB02, KC01 (see below for synonymy)
| |--G. glutinosusBB02
| `--G. roseusW01
|--Psiloboletinus Singer 1945KC01
|--Truncocolumella Zeller 1939 [incl. Dodgea Malençon 1939]KC01
| `--T. citrinaKB97
`--Suillus Gray 1821BB02, KC01 (see below for synonymy)
| i. s.: S. imbellus (Trappe) Kretzer & Bruns 1997 (see below for synonymy)KB97
| S. pictusJK06
|--+--S. asiaticusKB97
| `--+--S. cavipesKB97 [=Boletinus cavipesBB02]
| `--+--S. ochraceoroseusKB97
| `--S. palusterKB97
`--+--+--+--S. grevillei (see below for synonymy)KB97
| | `--S. tridentinusKB97
| `--+--S. grisellusKB97
| `--S. laricinusKB97
`--+--+--+--S. caerulescensKB97
| | `--S. lakeiKB97
| `--+--S. sinuspaulianusKB97
| `--S. spectabilisKB97
`--+--+--+--+--S. decipiensKB97
| | | `--S. spragueiKB97
| | `--+--S. granulatusKB97
| | `--S. placidusKB97
| `--+--+--S. (sect. Hirtellini) subaureusW01, KB97
| | `--+--S. (sect. Suillus) cothurnatusW01, KB97
| | `--S. subluteusKB97
| `--+--+--S. intermediusKB97
| | `--S. subalutaceusKB97
| `--+--S. umbonatusKB97
| `--+--S. americanusKB97
| `--S. sibiricusKB97
`--+--+--S. (sect. Fungosi) bovinusW01, KB97
| `--+--S. punctipesKB97
| `--+--S. tomentosusKB97
| `--+--S. variegatusKB97
| `--+--S. amaranthii (Thiers) Kretzer & Bruns 1997 (see below for synonymy)KB97
| `--S. suilloides (Thiers) Kretzer & Bruns 1997 (see below for synonymy)KB97
`--+--S. collinitusKB97
|--S. granulatusKB97
|--S. pungensKB97
`--+--+--S. glandulosipesKB97
| `--S. neoalbidipesKB97
`--+--+--S. brevipesKB97
| `--S. weaveraeKB97
`--+--S. luteusKB97
`--S. pseudobrevipesKB97

Nomen nudum: Gastrosuillus umbrinusKB97

Gomphidius Fr. 1836BB02, KC01 [=Gomphus (Fr.) Weinm. 1826 non (Pers.) Pers. 1797KC01, Leucogomphidius Kotl. & Pouzar 1972KC01]

Rhizopogon Fr. & Nordholm 1817BB02, KC01 [incl. Anthracophlous Mattir. ex Lloyd 1913KC01, Hysteromyces Vittad. 1844KC01, Splanchnomyces Corda 1831KC01]

Suillus Gray 1821BB02, KC01 [=Ixocomus Quél. 1888KC01, Peplopus (Quél.) Quél. ex Moug. & Ferry 1887KC01, Viscipellis (Fr.) Quél. 1886KC01; incl. Boletinus Kalchbr. 1867KC01, Boletopsis Henn. 1898 non Fayod 1889KC01, Cricunopus Karst. 1881KC01, Eryporus Quél. 1886KC01, Euryporus Quél. 1886KC01, Fuscoboletinus Pomerl. & Sm. 1962KC01, Gastrosuillus Thiers 1989KC01, Gymnopus (Quél.) Quél. ex Moug. & Ferry 1887 non (Pers.) Roussel 1806KC01, Mariaella Šutara 1987KC01, Pinuzza Gray 1821KC01, Rostkovites Karst. 1881KC01, Solenia Hill ex Kuntze 1898 non Pers. 1794KC01]

Suillus amaranthii (Thiers) Kretzer & Bruns 1997 [=Gastrosuillus amaranthii Their 1989]KB97

Suillus grevillei [=Boletus grevillei Klotzsch: Fries 1832; incl. Gastroboletus laricinus Singer & Both 1977, Gastrosuillus laricinus (Singer & Both) Thiers 1989]KB97

Suillus imbellus (Trappe) Kretzer & Bruns 1997 [=Gastroboletus imbellus Trappe 1969, Gastrosuillus imbellus (Trappe) Thiers 1989]KB97

Suillus suilloides (Thiers) Kretzer & Bruns 1997 [=Gastroboletus suilloides Thiers 1969, Gastrosuillus suilloides (Thiers) Thiers 1989]KB97

*Type species of generic name indicated


Bessette, A. E., W. C. Roody & A. R. Bessette. 2000. North American Boletes: A color guide to the fleshy pored mushrooms. Syracuse University Press.

[BB02] Binder, M., & A. Bresinsky. 2002. Derivation of a polymorphic lineage of Gasteromycetes from boletoid ancestors. Mycologia 94 (1): 85–98.

[JK06] James, T. Y., F. Kauff, C. L. Schoch, P. B. Matheny, V. Hofstetter, C. J. Cox, G. Celio, C. Gueidan, E. Fraker, J. Miadlikowska, H. T. Lumbsch, A. Rauhut, V. Reeb, A. E. Arnold, A. Amtoft, J. E. Stajich, K. Hosaka, G.-H. Sung, D. Johnson, B. O’Rourke, M. Crockett, M. Binder, J. M. Curtis, J. C. Slot, Z. Wang, A. W. Wilson, A. Schüßler, J. E. Longcore, K. O’Donnell, S. Mozley-Standridge, D. Porter, P. M. Letcher, M. J. Powell, J. W. Taylor, M. M. White, G. W. Griffith, D. R. Davies, R. A. Humber, J. B. Morton, J. Sugiyama, A. Y. Rossman, J. D. Rogers, D. H. Pfister, D. Hewitt, K. Hansen, S. Hambleton, R. A. Shoemaker, J. Kohlmeyer, B. Volkmann-Kohlmeyer, R. A. Spotts, M. Serdani, P. W. Crous, K. W. Hughes, K. Matsuura, E. Langer, G. Langer, W. A. Untereiner, R. Lücking, B. Büdel, D. M. Geiser, A. Aptroot, P. Diederich, I. Schmitt, M. Schultz, R. Yahr, D. S. Hibbett, F. Lutzoni, D. J. McLaughlin, J. W. Spatafora & R. Vilgalys. 2006. Reconstructing the early evolution of Fungi using a six-gene phylogeny. Nature 443: 818–822.

[KC01] Kirk, P. M., P. F. Cannon, J. C. David & J. A. Stalpers. 2001. Ainsworth & Bisby’s Dictionary of the Fungi 9th ed. CAB International: Wallingford (UK).

[KB03] Kjøller, R., & T. D. Bruns. 2003. Rhizopogon spore bank communities within and among California pine forests. Mycologia 95 (4): 603–613.

[KB97] Kretzer, A., & T. D. Bruns. 1997. Molecular revisitation of the genus Gastrosuillus. Mycologia 89 (4): 586–589.

[NU03] Nagao, H., S. Udagawa, N. L. Bougher, A. Suzuki & I. C. Tommerup. 2003. The genus Thecotheus (Pezizales) in Australia: T. urinamans sp. nov. from urea-treated jarrah (Eucalyptus marginatus) forest. Mycologia 95 (4): 688–693.

[RG97] Rodríguez Gallart, C. A. 1997. Estudios en los micromicetos de la Republica Dominicana, III. Moscosoa 9: 145–153.

[W01] Watling, R. 2001. The relationships and possible distributional patterns of boletes in south-east Asia. Mycological Research 105 (12): 1440–1448.

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