Suillus Gray sect. Suillus

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 Gray sect. Suillus

Etymology.

autonym.

Typification.

Suillus luteus (L.) Roussel

Morphology.

Basidiomata stipitate-pileate with tubular hymenophore. Pileus develops from hemispherical to convex or plane, viscid to glutinous, glabrous, with small color streaks that resemble fine fibrils in some species. Cap is usually covered with a layer of greyish or brown glue when young that dries out or remains viscid. Background color white or yellowish white when young, becoming yellow or dark yellow with age. Cap color varies from whitish yellow to dark brown at maturity. Hymenophore adnate to subdecurrent, pores 1–2 per mm, round to angular, radially arranged, younger ones are usually beaded with white, yellowish or pinkish droplets. Context whitish yellow to yellow in pileus and stipe. Stipe context sometimes changing color to blue, greenish blue, reddish or brownish. Stipe equal to clavate, solid, glandular dots always present, whitish, yellow or reddish when young, becoming cinnamon brown or brown with age. Veils absent except in the clade of Suillus luteus and S. aestivoluteus . When present, veil superior, white, cottony or sheer texture. Mycelia always white or pinkish. Spore print dull cinnamon, brown, or cinnamon brown.

Basidiospores smooth, oblong and inequilateral, hyaline yellow to ochraceous brown in KOH, usually 7–11 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 material in KOH. Pileipellis a layer of gelatinous hyphae, with yellowish hyaline content in KOH. Clamp connections absent.

Habitat.

Scattered to gregarious, ectomycorrizal with Pinus subg. Pinus and Strobus .

Known species.

Suillus aenoplacidus , S. albivelatus , S. anomalus , S. bellinii , S. borealis , S. brevipes , S. brunnescens , S. collinitus , S. flavopunctipes , S. fluryi , S. glandulosipes , S. granulatus , S. indicus , S. kaibabensis , S. longiflavopunctipes , S. luteus , S. aestivoluteus , S. marginielevatus , S. mediterraneensis , S. neoalbidipes , S. occidentalis , S. placidus , S. pseudoalbivelatus , S. psuedobrevipes , S. pungens , S. quiescens , S. subalpinus , S. triacicularis , S. volcanalis , S. wasatchicus , S. weaverae and S. zangii .

Notes.

For this section, pileus is always glabrous, some species have small greyish or brown color streaks resembling fine fibrils. Most species have a glutinous layer over the cap, and the glue appears greyish or brown in younger sporophores. Stipe background color is often white to yellowish white. Glandular dots always present, and usually develop from light color to cinnamon brown or brown with age. Partial veils are absent except in the clade of Suillus luteus and S. aestivoluteus . These two species have both appendiculate veil remnants on the cap margin and an annulus on stipe. Spore print always dull cinnamon, brown, or cinnamon brown. Cheilocystidia, pleurocystidia and caulocystidia are always abundant. In general, morphological characters alone are not sufficient for delimiting section Suillus from section Diversipedes . Both Pinus subg. Pinus and Strobus are hosts for the section.

The current delimitation of the two sections is supported by phylogenies of RPB 2 and concatenated datasets (Table 3 . Morphological features are not effective in separating the two sections. In general, section Suillus is morphologically more consistent with the presence of a glutinous pileus and glandular dots. In micromorphology, section Suillus always has a layer of gelatinous hyphae on pileus and a stipe with caulocystidia in fascicles. Host association does not help delimit the two sections because both are associated with Pinus subgenera Pinus and Strobus . Geographic ranges of the two sections overlap.

Estadès and Lannoy (2001) included the type of the genus Suillus , S. luteus in the Suillus sect. Granulati . However, according to the Article 22.2 of the International Code of Nomenclature for algae, fungi, and plants (“ A name of a subdivision of a genus that includes the type of the legitimate name of the genus is not validly published unless its epithet repeats the generic name unaltered ”), the name of the section is invalid as this section contains the type of the genus Suillus . Many synonymous species are found in the Suillus pseudobrevipes complex ( Nguyen et al. 2016; Suppl. material 1: fig. S 2). The ITS phylogeny only supports one species in the Suillus pseudobrevipes complex and morphological variations across different developmental stages are found to be common in this complex. This may suggest S. pseudobrevipes complex is an actively evolving species complex. Genetic isolation by physical barriers (ex: high mountains, islands) leads to separation and speciation. Therefore, these synonyms may represent multiple species instead of morphotypes in different developmental stages.