Suillus minusculus 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 minusculus R. Zhang, X. F. Shi, G. M. Mueller & P. G. Liu sp. nov.

Figs 18 , 19

Etymology.

The epithet refers to the small size of the species.

Diagnosis.

The diameter of the pileus is 3–4.5 cm and it is among the smallest of known Suillus species.

Typification.

China: • Guangdong Province, Ruyuan, Shaoguan, Nanling National Forest Park (24°53'50.10"N, 113°01'37.22"E, alt. 1200 m), 18 September 2015, Bo Li, Libo 113 (holotype, HKAS 89874 ) .

GenBank.

ITS = KU 721492 ; LSU = KY 489974 ; TEFα- 1 = KU 721706 ; RPB 1 = KU 852193 ; RPB 2 = KU 852352 .

Morphology.

Pileus develops from convex to plane, eventually depressed, 3–4.5 (- 5) cm diameter, surface viscid when moist, background color yellowish brown (4 A 4, 4 B 4), covered with closely appressed dark brown (5 E 7,5E 8). Hymenophore decurrent, yellow (4 A 7, 4 B 7), pores comparatively large, 1 per mm, angular, compound, radially arranged, smaller towards the margin. Tubes 3–5 mm long, concolorous with the pores. Stipe 3.0–4.0 × 0.3–0.5 cm, cylindrical, solid, veil white and membranous, turning blackish when bruised, lost in age. Reticulate above the annulus. Glandular dots abundant, distribute mainly below the annulus, vinaceous brown (6 D 7). Context yellow in pileus and stipe, does not change color. Pileus context thin, no more than 4 mm thick. Spore print reddish brown (6 E 5). Odor and taste indistinctive.

Basidiospores [80 / 1 / 2] (8.5) 9.0–11.0 × 3.5–4.5 μm, Q = 2.13–2.50 (2.57), Q sd = 2.36 ± 0.13, smooth, oblong in face view, narrowly inequilateral with a hilar appendage in profile view, brown or ochraceous in KOH, tawny yellow in Melzer’s. Basidia 4 - spored, clavate, bulbous, 21.0–28.0 × 6.0–8.5 μm, hyaline yellow or brown in KOH, tawny yellow in Melzer’s. Hymenophoral trama divergent, wrinkled, thin-walled, hyaline and mostly 5–8 (- 12) μm. Pleuro- and Cheilocystidia in fascicles, abundant, clavate, contents brown or hyaline, surrounded by brown amorphous material in KOH, up to 80 μm long. Pileipellis outer most a layer of hyphae light ochraceous or hyaline in KOH, smooth, most 3–7 μm; underneath a gelatinous layer with hyphae densely encrusted with ochraceous granules, most 3–7 (- 11) μm wide. Stipitipellis mostly composed of interwoven hyphae, covered by brown amorphogous pigments, about 3–10 μm wide. Caulocystidia abundant along stipe, morphologically similar with pleuro- and cheilocystidia, encrusted with brown pigments in KOH, up to 100 μm long. Context trama hyaline, smooth, thin-walled, interwoven, similar in pileus and stipe, mostly 3–30 μm, up to 40 μm wide at stipe base. Clamp connections absent.

Habitat.

Scattered, in association with Pinus kwangtungensis .

Known distribution.

Currently only known from the Nanling National Forest Park in Guangdong.

Specimens examined.

China: • Guangdong Province, Ruyuan, Shaoguan, Nanling National Forest Park (24°53'47.02"N, 113°01'36.05"E, alt. 1209 m), 18 September 2015, Rui Zhang, Rui 363 ( HKAS 90665 ) ; ibid 17 September 2011, Xiaofei Shi, Shi 979 ( HKAS 71980 ) .

Notes.

Pinus kwangtungensis is a rare pine species and forms a large forest only in the Nanling National Forest Park; it seems that S. minusculus is also rare and should be under conservation.

Figures

Figure 18. Basidiomata of Suillus minusculus (paratype, HKAS 71980). Scale bar: 5 cm.

Figure 19. Suillus minusculus (paratype, HKAS 71980). a Basidiospores; b Cheilocystidia; c Hymenium with basidia; d Pileipellis (mature specimens). Scale bars: 5 μm (a); 20 μm (b – d).