Suillus Gray subg. Suillus, Gray

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 subg. Suillus

Typification.

Suillus luteus (L.) Roussel

Diagnosis.

This subgenus contains numerous species with a wide spectrum of morphological variations. All are associated with Pinus except two species. The clamp connections are lacking.

Morphology.

Basidiomata stipitate-pileate with tubular hymenophore. Pileus develops from hemispherical or convex to subconvex, plane or umbonate, sometimes with wavy margin, viscid to glutinous or dry, glabrous or covered with fibrils or scales. Background color of the cap varies from ivory to yellow. Some species are covered with yellowish, pinkish, red or brown fibrils or scales. Cap color highly variable, colors include ivory, yellowish white, yellow, brown, dark brown, olive brown, olive, pinkish, and red. Hymenophore adnate, subdecurrent or decurrent, pores 1–2 per mm occasionally up to 5 mm diameter, round to angular, radially arranged or almost lamellate. Some younger ones beaded with white or yellowish droplets. Pores and tubes in some species changing color to brownish or light blue when bruised or cut. Pileus and Stipe Context white, whitish yellow, yellow or light orange. Stipe context sometimes changes color to blue, greenish blue, reddish or brownish. Stipe equal to clavate, solid, with or without glandular dots, glandular dots whitish, yellow, reddish, brown, or cinnamon brown when young, becoming cinnamon brown or brown with age. With or without annulus, annulus often superior, white, pinkish or brownish, persistent or evanescent, fibrillose, cottony, gelatinous, glutinous or membranous. Mycelia often white or pinkish, sometimes changing color to pinkish or red when bruised. Spore print olive, brown, cinnamon brown or olive 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 in fascicules, large, up to 100 μm, with brown content and surrounded by brown amorphous material in KOH, some species lack caulocystidia. Pileipellis a layer of gelatinous hyphae, with yellowish hyaline content in KOH; some species with a layer of scales that are smooth and light ochraceous in KOH. Clamp connections absent.

Habitat.

Scattered to gregarious, ectomycorrizal with Pinus as primary the host and Larix as the secondary host.

Known species.

Listed in section Suillus and Diversipedes .

Notes.

Lofgren et al. (2021) and Zhang et al. (2022) resolved the subgenera within genus Suillus using multigene phylogenies. This subgenus is strongly supported as monophyletic by phylogenies of the supermatrices, TEFα- 1 and RPB 2 genes. This subgenus is the most species rich in genus Suillus , containing more species than all other subgenera combined.

Morphological features alone are not very informative for distinguishing species in this subgenus from others. Glandular dots, or caulocystidia visible under the microscope, are exclusive for this subgenus. But not all species in the subgenus have glandular dots. Partial veils may or may not be present. Pilei vary from glabrous to scaly, dry to glutinous and white to a large variety of colors. Micromorphological features are even less effective in delimiting the Suillus subgenera. Host association with Pinus stands out as the key to differentiate species in this subgenus from those in the other subgenera.