Suillus subg. Fuscoboletinus (Pomerl. & A. H. Sm.) R. Zhang, X. F. Shi, G. M. Mueller & P. G. Liu, 2025

Shi, Xiaofei, Zhang, Shiru, Mueller, Gregory M., Liu, Peigui, Yu, Fuqiang & Senanayake, Indunil C., 2025, A subgeneric revision of the genus Suillus (Suillaceae, Boletales) and novel taxa from Eastern Asia based on morphology and multigene phylogenies, IMA Fungus 16, pp. e 144260-e 144260 : e144260-

Suillus subg. Fuscoboletinus (Pomerl. & A. H. Sm.) R. Zhang, X. F. Shi, G. M. Mueller & P. G. Liu comb. & stat. nov.

Basionym.

Fuscoboletinus Pomerl. & A. H. Sm. , Brittonia 14: 157 (1962)

Typification.

Fuscoboletinus sinuspaulianus Pomerl. & A. H. Sm.

Etymology.

The subgenus name is referred from its type, Fuscoboletinus sinuspaulianus .

Diagnosis.

The subgenus differs from other subgenera mainly by spore print color. Pileus is usually red, and viscid to glutinous. Veils is glutinous, or dry and fibrillose. Glandular dots are lacking. Spore print is purplish brown in mass. Clamp connections are absent and associated with Larix .

Morphology.

Basidiomata stipitate-pileate with tubular hymenophore. Pileus develops from hemispherical to convex or applanate, viscid to glutinous, usually red to brown in maturity, with or without scales or fibrils, with appendiculate veil remnants; context yellow, no color change when cut or slowly turning to pinkish and brown. Hymenophore boletinoid, separable, pores up to 2 mm, angular or irregular, and radially arranged. Stipe subcylindrical to cylindrical, solid, lacking glandular dots; veil viscid or dry and floccose; stipe surface floccose or viscid. Spore print purplish brown.

Basidiospores smooth, oblong and inequilateral, hyaline yellow in KOH, usually 7–11 μm, one species has large basidiospores 12–14 μm. Basidia 4 - spored, clavate, hyaline yellow in KOH. Cystidia abundant, typically fasciculate, large, up to 100 μm, with brown content and surrounded by brown amorphous materials in KOH. Pileipellis a layer of gelatinous hyphae, with yellowish hyaline content in KOH. Clamp connections absent.

Habitat.

Scattered to gregarious, ectomycorrizal with Larix .

Known species.

Suillus glandulosus , S. sinuspaulianus and S. spectabilis .

Notes.

The grouping of S. spectabilis , S. sinuspaulianus , and S. glandulosus was not found in older mycological references. Singer (1986) placed Suillus spectabilis and S. ochraceoroseus in section Solidipedes , and S. sinuspaulianus and S. glandulosus in section Glandulosi . Pomerleau and Smith (1962) classified all three species in the genus Fuscoboletinus along with several species from other Suillus subgenera (Table 1 ). Subgenus Fuscoboletinus is the less speciose subgenus in genus Suillus .

Further studies are required for identifying hosts of S. sinuspaulianus and S. glandulosus and for determining whether the two are better treated as synonyms ( Nguyen et al. 2016). Reported hosts of S. sinuspaulianus are Pinus sp. , Abies balsamea and Picea glauca in Canada ( Pomerleau and Smith 1962). Documented hosts of S. glandulosus are Abies balsamea in Quebec ( Canada) and Thuja occidentalis in Michigan ( USA) ( Pomerleau and Smith 1962). The hosts of this species have never been confirmed from colonized mycorrhizal root tips, but phylogeny is well-supported to place this species within the Larix associated Suillus clade. Therefore, Nguyen et al. (2016) suggests that Larix species could be the primary host. However Pérez-Pazos et al. (2021) showed that Picea and Abies can also be secondary hosts. However, none of the hosts have been adequately confirmed. Collections of Suillus spectabilis from northeastern China were supported as conspecific with North American counterparts by GCPSR and coalescence. Population genetic studies are needed to assess the genomic divergence of S. spectabilis populations across the continents.