Sutorius rubinus Vadthanarat, Raspé and Lumyong.
Pileus 4.5–7.5 cm in diameter, convex to planoconvex, with slightly deflexed, becoming straight margin, which is slightly exceeding (1–2 mm) especially when young; surface at first subrugulose to rugose becoming scabrous to subrugulose at center, tomentose, reddish dark brown (9F4–6) becoming reddish dark brown (8F5–8) to reddish brown (8D/E6–8) with age, gradually paler to the margin. Pileus context 5–10 mm thick halfway to the margin, orange white (5A2), with scattered small groups of reddish brown (8–9D4–5) encrustations. Stipe central, terete to slightly compressed, cylindrical to subclavate or tapering downwards, sometimes with subbulbous base, 5–6.5 _ 0.8–2.2 cm; surface finely scabrous, reddish gray to grayish brown (8 D/E 2–3) densely covered with reddish brown to dark brown (8F4–5) granulose squamules; basal tomentum white to off-white. Stipe context solid, orange white to pinkish white (5A2 to 7A2), reddish to grayish brown to dark brown (8D–F3–5) virgate, with scattered small groups of reddish brown (8–9D4–5) encrustations, unchanged or slightly reddening when cut. Hymenophore tubulose, adnexed to narrowly adnexed, ventricose, slightly depressed around the stipe; tubes dull yellowish white (3A3–4) when young becoming orange-brown (7E7) with age, easily separable, 6–11 mm long halfway to the margin; pores 0.3–0.5 mm wide at midradius, mostly roundish, at first grayish orange (5D3–4) becoming orange to pale orange (5A3–4 to 6B6–7) with age, with scattered small groups of reddish dark brown (8F3–4) encrustations. Odor and taste not observed. Spore print not observed. Macrochemical reactions: KOH: dark brown to black on the stipe, reddish on the hymenophore, negative on the pileus, pileus context, and stipe context. Basidiospores [168/3/3] (8.7–) 9.6–10.8–12.1 (–13.1) _ (3.5–)3.9–4.3–4.8 (–5.1) mm, Q = (2.03–) 2.2–2.5–2.82 (–2.96). Form the type (8.7–) 9.3 10.5–12.1 (–12.3) _ (3.5–) 3.9–4.4–4.9 (–5.1) mm, Q = (2.03–) 2.06–2.4–2.73 (–2.81), N = 57, narrowly ellipsoid to subcylindrical with slightly suprahilar depression, thin-walled, smooth, yellowish hyaline in KOH or NH4OH, inamyloid Basidia 4-spored (23–) 23–27–31 (–31) _ (10–) 10– 11–13 (–13) mm, with sterigmata up to 4 mm long, clavate, hyaline, inamyloid. Cheilocystidia (20–) 20–26–32 (–32) _ (5–)5–7–8 (–8) mm, frequent, narrowly fusiform to fusiform with subacute apex, thin-walled, hyaline. Pleurocystidia not seen. H. trama divergent, 42–80 mm wide, with regular to subregular mediostratum 8–27 mm wide. Pileipellis an intricate trichoderm to slightly gelatinized intricate trichoderm, 60–110 mm thick, made of densely interwoven, thin-walled, smooth, hyaline hyphae 4–12 mm wide, with terminal cells 11–40 _ 5–12 mm, fusiform to broadly fusiform with acuminate apex, slightly yellowish to reddish pale brown in water, mostly hyaline to yellowish pale brown in KOH or NH4OH. Pileus context made of strongly interwoven hyphae, 6–18 mm wide, thinwalled, with scattered loose crystals. Stipitipellis a disrupted hymeniderm, 90–120 mm thick, composed of parallel hyphae, thin-walled, with terminal cells 19–30 _ 11–14 mm, giving rise to clusters of caulocystidia and basidiole-like cells, with scattered encrustations. Caulocystidia (23–) 23–31–40 (–40) _ (8–) 8–12–18 (–18) mm, frequent, fusiform with subacute apex, thin-walled, hyaline. Stipe context composed of parallel, 8- to 12-mm-wide hyphae, with scattered encrustations. Clamp connections not seen in any tissue. (Fig. 1A–F, 2)
Habitat: Solitary to gregarious, on soil, in evergreen hill forest dominated by Castanopsis spp., Lithocarpus spp. mixed with D. tuberculatus, D. obtusifolius, Sh. obtusa, and Sh. siamensis.
Distribution: Chiang Mai Province, Northern Thailand
Specimens examined: THAILAND: Chiang Mai Province: Mae On District, Ban Huay Keaw community forest, 18_510550 0N–99_170230 0E, elev. 710 m, June 4, 2012, Jie Chen and Olivier Raspé, OR0379 (MFLU12-0231);Mae Taeng District, Pha Deng village, 19_060380 0N–98_440320 0E, elev. 1,055 m, June 7, 2012, Olivier Raspé and Komsit Wisitrassameewong, OR0409 (MFLU12-0261); ibid., June 24, 2016, Olivier Raspé, OR1255 (CMUB, BR).
Notes: S. rubinus is characterized by the following combination of characteristics: medium-sized basidiomata, dark reddish brown to reddish brown; lack of pleurocystidia; pileipellis a trichoderm with fusiform to broadly fusiform terminal cells with acuminate apex. Phylogenetically, all S. rubinus specimens formed a clade (clade 9) close to three Sutorius species including S. pachypus (clade 10), S. australiensis (clade 11), and S. mucosus (clade12). Nevertheless, they are morphologically different from S. rubinus as follows: S. pachypus has on average wider (2.5–4 cm wide) stipe and has pleurocystidia, and the pileipellis is a palisadoderm composed of subcylindrical with rounded to subacute apex. S. australiensis has dark violet brown pores when young, a trichoderm pileipellis composed of elongated to cylindrical elements with obtuse apex and is found only in Australia. S. mucosus has a waxy to subviscid pileus with an ixotrichoderm forming the pileipellis composed of gelatinized hyphae, with fusiform to utriform terminal cells with rounded to subacute 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.