Sutorius pachypus Vadthanarat, Raspé and Lumyong sp.
Pileus 4.5–9 cm in diameter; at first hemispherical then convex to planoconvex with deflexed, slightly exceeding margin (1–2 mm); surface subrugulose, dull, minutely tomentose, at first dark reddish brown to dark brown (9F5–6) becoming pale reddish brown (8–9D/E4–7), gradually paler to the margin. Pileus context 1.5–1.7 cm halfway to the margin, pale grayish orange (6A2) to purplish gray (17C3, 17D4) at place, with scattered small group of dark reddish brown (9F5–6) encrustations, unchanging or slightly reddening when cut. Stipe central, wide, cylindrical (5.5) 6–6.5 _ 2.5–4 cm; surface even to finely scabrous, dry, reddish to grayish gray (10B–D2) darker at the base (10D/E3), with pale violet gray (10D2) to violet brown (10F3–4) granulose squamules; basal tomentum little developed, white. Stipe context solid, orange white (5A2), yellowish orange to purplish gray (6D5, 12D/E3) virgate, slightly reddening when cut (especially near the base). Hymenophore tubulose, adnexed, slightly depressed around stipe; tubes easily separable, pale orange (5A2), 10–12mmlong halfway to the margin; pores at first dark violet brown (11F4) becoming brown (8F5–6). Spore print not recorded. Macrochemical reactions: KOH: yellowish brown on pileus and stipe; NH4OH: yellowish brown with greenish to pinkish aura on pileus; orange with blue green aura on stipe. Basidiospores from the type (immature) (5.8–) 6.6–7.5-8.4(–8.8) _ (2.9–) 3.2–3.7–4.2 (–4.4) mm, Q = (1.6–) 1.7–2.04–2.41 (–2.47), N = 55, oblong to ellipsoid with suprahilar depression, thin-walled, smooth, yellowish to brownish hyaline in water, yellowish hyaline in KOH or NH4OH, inamyloid. From voucher TWO1171 (9–) 9.5–11–13.6 (–14) _ (3.9–) 3.9–4.4–4.9 (–5.2) mm, N = 50 Q = (2.06–) 2.18–2.51–2.98 (–3.11), narrowly ellipsoid to subcylindrical with suprahilar depression, thin-walled, smooth, yellowish to brownish hyaline in water, yellowish hyaline in KOH or NH4OH, inamyloid. Basidia 4-spored, rarely 2-spored (24–) 25–28–34 (–36) _ (8–) 8–9–11(–13) mm, with sterigmata up to 4.5 mm long, narrowly clavate to clavate, hyaline, inamyloid. Cheilocystidia (20–) 22–30–39 (–43) _ (4–) 4–7–11 (–11) mm, frequent, narrowly fusiform to fusiform, thin-walled, hyaline. Pleurocystidia (29–) 29–34–40 (–40) _ (5–) 5–6–7 (–7) mm, infrequent to rare, same shape as the cheilocystidia, thin-walled, hyaline. H. trama divergent 45–78 mm wide, with subregular mediostratum 18–26 mm wide. Pileipellis a palisadoderm when young becoming trichoderm, 97–128 mm thick, composed of thin-walled hyphae, with terminal cells 16–47 _ 3–7.5 mm, cylindrical to subcylindrical with rounded to subacute apex somewhere, slightly yellowish to reddish pale brown in water, mostly hyaline to yellowish pale brown somewhere in KOH or NH4OH. Pileus context made of strongly interwoven hyaline hyphae, 6–16.5 mm wide, with scattered loose crystals. Stipitipellis a disrupted hymeniderm, 80–110 mm thick, composed of parallel hyphae, with terminal cell 13–43 _ 5–9.5 mm of thin-walled, hyaline hyphae, giving rise to clusters of caulocystidia, basidiole-like cells and scarce basidia, with scattered encrustations. Caulocystidia (24–) 25–35–51 (–55) _ (7–) 8–10–14 (–14) mm, frequent in groups, fusiform, thin-walled, hyaline. Stipe context composed of parallel 4- to 13.5-mm-wide hyphae, with scattered encrustations. Clamp connections not seen in any tissue.
Habitat: Solitary to gregarious, on soil, in hill evergreen forest dominated by Castanopsis spp., Lithocarpus spp. mixed with Sh.obtusa, Sh. siamensis, D. obtusifolius and D. costatus.
Distribution: Chiang Mai Province, Northern Thailand.
Specimen examined: THAILAND: Chiang Mai Province: Mae Taeng District, Behind Wat Pah Deng, 19_0603100N–98_4402800E, elev. 1,070 m, July 7, 2015, Santhiti Vadthanarat, SV0098 (CMUB, BR). –ibid., Baan Mae Sae, Highway 1095 at km 55, 19_14032.600N–98_38029.400E, elev. 990 m, June 10, 2006, Osmundson, TWO1171 (MFLU, NY).
Notes: S. pachypus is characterized by the following combination of characteristics: medium-sized basidiomata; wide cylindrical stipe with granulose squamules on the stipe surface that mostly are pale violet gray to violet brown at places; pileipellis is a palisadoderm to trichoderm, subcylindrical terminal cells with rounded to subacute apex; presence of cheilocystidia and pleurocystidia. The holotype (OR0411) has oblong to ellipsoid basidiospores because it is immature. However, a mature specimen (TWO1171) has the typical shape of basidiospores, which are narrowly ellipsoid to subcylindrical with suprahilar depression. The specimen (TWO1171) was originally morphologically identified as S. eximius, but our more detailed examination and phylogenetic analyses indicate a new species, S. pachypus. Phylogenetically, S. pachypus formed a clade (clade 10) closely related to S. rubinus (clade 9), S. australiensis (clade 11), and S. mucosus (clade 12). However, all of those differ from S. pachypus mainly in having a narrower stipe with darker granulose squamules. The other differences are as follows: S. rubinus has redder basidiomata, lacks pleurocystidia, and has a trichoderm pileipellis with fusiform to broadly fusiform terminal cells with acuminate apex. S. australiensis has darker violet–brown pores (when young), and it has been found so far only in Australia. S. mucosus lacks both cheilocystidia and pleurocystidia and has a waxy to subviscid pileus, an ixotrichoderm pileipellis with fusiform to utriform terminal cells with rounded to tapering apex.
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)