Sutorius obscuripellis Vadthanarat, Raspé and Lumyong.
Pileus (3.5) 4.5–6 cm in diameter convex to planoconvex, with straight margin; surface even, minutely and densely matted tomentose, dull, violet–brown to dark brown (10F5–6 to 9E4), with patchy color variation, sometimes gradually paler to margin. Pileus context 6–9 mm thick halfway to the margin, yellowish white (4A2), more brownish near the pellis, slowly turning pale red–brown when cut, with scattered small groups of reddish brown to dark brown (9E4–5, 9F5–6) encrustations. Stipe clavate to cylindrical (3.5) 3.8–5.5 × 0.8–1.7 cm; surface dull, even to finely scabrous, violet-gray (18D2, 16E2) with violet–brown (10E43–5) granulose squamules; basal tomentum off-white to yellowish white. Stipe context solid, fleshy fibrous, light purplish brown (12B2), more purplish at the base, with scattered small groups of reddish brown to dark brown (9E4– 5, 9F5–6) encrustations. Hymenophore tubulose, adnexed to adnate, depressed around stipe, ventricose; tubes orange–gray (6B2), 6–13 mm long, easily separable, turning red–brown on bruising; pores 0.2–0.5 mm wide at midradius, roundish, regularly arranged, with subregular pore surface, pale violetgray (9–10B3), becoming paler with age, slightly reddish brown on bruising, with scattered small groups of reddish brown to dark brown encrustations, composite pores uncommon. Odor not recorded. Taste slightly bitter at first, then mild. Spore print not recorded. print not recorded. Macrochemical reactions: KOH: dull yellow on pileus; yellow or pale yellow on pileus context, stipe, stipe context, and hymenophore. NH4OH: yellowish with only slight violet aura on pileus; yellowish on stipe and pileus context; negative on hymenophore and stipe context. Basidiospores (9.6–)9.8–10.8–12.2 (–13.5) × (3.6–) 3.8–4.2– 4.6 (–5.1) µm, Q = (2.19–) 2.34–2.55–2.83 (–2.97), N = 72, narrowly ellipsoid to subcylindrical with slightly suprahilar trichoderm, 100–170 µm thick, made of loosely interwoven terminal cells 17–65 × 3–6 µm, with subacute to rounded apex, brown to dark in water especially the terminal cells, less brown in KOH or NH4OH. Pileus context composed of moderately interwoven, 6- to 12 (15)-µm-wide hyphae, brownish to yellowish hyaline, with some scattered parietal encrustations and loose crystals. Stipitipellis a disrupted hymeniderm 100– 125 µm thick, composed of parallel hyphae, anastomosing at places, with terminal cell 10–24 × 6–12 µm of thin-walled hyaline hyphae, giving rise to clusters of caulocystidia and basidiole-like cells, with scattered loose crystals. Caulocystidia (19–) 20–26–38 (–38) × (6–) 6–11–20 (–22) µm, broadly fusiform, thin-walled, hyaline. Stipe context composed of parallel 5- to 8 (12)-µm-wide hyphae, with scattered loose crystals. Clamp connections not seen in any tissue. (Fig. 2 d–g; Fig. 3)
Habitat: On soil, gregarious to fasciculate in hill forest dominated by Castanopsis spp. Lithocarpus spp. mixed with some Dipterocarpus spp. and regularly subject to fire.
Distribution: Chiang Mai Province, Northern Thailand.
Notes: Based on a single collection (OR0949), S. obscuripellis is characterized by the following combination of characteristics: basidiomata small- to medium-sized; pale violet–gray pores color; lack of pleurocystidia; Pileipellis an intricate trichoderm composed of brown to dark hyphae with cylindrical terminal cells with subacute to rounded apex, showing scattered small parietal brownish yellow to reddish pale to dark brown encrustations. Phylogenetically, S. obscuripellis formed a clade (clade 8) sister to Sutorius ubonensis (clade 7) and S. subrufus (clade 6). However, the latter two species are morphologically different from S. obscuripellis as follows: S. ubonensis has larger basidiomata, darker pores, and basidiomata especially when young, pleurocystidia, and a slightly gelatinized tomentose pileipellis, and has so far only been found in dry dipterocarp forest in Ubon Ratchathani Province, in northeastern Thailand. S. subrufus has larger basidiomata, a stipe surface and context turning more reddish when injured, presence of pleurocystidia, and a trichoderm pileipellis composed of cylindrical hyphae and clavate or subclavate terminal cells with obtuse apex, colorless to yellowish in KOH (Chai et al., 2019), whereas S. obscuripellis has the pileipellis composed of brown to dark brown hyphae, colorless to brownish yellow to pale brown in KOH.
Fig. 1 Phylogenetic tree inferred from the three-gene dataset (atp6, rpb2 and tef1), of Sutorius species and selected Boletaceae in Pulveroboletus group, using Maximum Likelihood and Bayesian Inference methods (ML bipartition tree is presented). The three Butyriboletus species were used as outgroup. All generic clades, excluding Sutorius, that were highly supported were collapsed. Seventeen species-level clades within Sutorius are indicated with label. Bootstrap support values (BS 70%) and posterior probabilities (PP 0.90) are shown above the supported branches. The star (*) indicates additional collections with exactly identical sequences or sequences differing only by heteromorphisms in tef1 (with the number of heteromorphisms mentioned in square brackets. (Phylogenetic tree from Vadthanarat et al 2021)