Sutorius ubonensis Vadthanarat, Raspé and Lumyong.
Pileus (5.5) 8.0–10.5(12) cm in diameter, at first hemispherical to convex with straight to slightly inflexed margin, becoming convex to planoconvex to depressed with straight to slightly reflexed margin, margin slightly exceeding (1–2 mm), elastic; surface evento subrugulose, dull, subviscid when wet, minutely tomentose, at first violet to violet brown (10E4) to dark brown (9F5–6), later become reddish gray (10B2) to dull red or brownish gray (10C/D3) at the center, getting paler to brownish gray to (8C2) near the margin, sometimes patchy of reddish gray (8–9C/E3–4) purplish brown (10F4–5) or brown (6E6). Pileus context 10–18 mm thick halfway to the margin, yellowish white to orange white (4A2 to 5A2), with scattered small groups of reddish brown (9D4–6) encrustations, unchanged. Stipe central, terete to subcompressed, cylindrical to subclavate or tapering downwards (4.8) 5.2–8.5 _ 1.8–3.2 cm; surface even to finely scabrous, slightly venose to rimose near the cap, dull to slightly shiny, dry, purplish gray to brownish gray (9–10C/E2), scattered of reddish brown to dark brown (9F4–5) granulose squamulose; basal tomentum off-white to yellowish white. Stipe context solid, slightly fibrous, yellowish white (4A2 to 5A2) to slightly purplish gray (15B/C2) near the stipitipellis, grayish brown to purplish brown (8–9E/F3–5) virgate, with scattered brownish gray (8–10E2) or reddish brown (9D4 to 9F4–5) encrustations, unchanged. Hymenophore tubulose, adnate, subventricose to ventricose; tubes easily separable, at first purplish to yellowish gray (8C2 to 6B3 to 5B3 4) becoming yellowish orange to brownish orange (5B3–4 to 6B3–4) with age, 8–13 mm long halfway to the margin; pores 0.3–0.8 mm wide at midradius, mostly roundish, slightly elongated near the stipe, subregular especially when young, dark brown to purplish dark brown (9F4–6 to 10F3–5) at first, become brown (7F5–6) to orange brown (6E4–5, 7E5–6) with age. Odor fungoid to slightly acidulate. Taste mild to slightly acid. Spore print brownish orange (7C3) to dark brown (7F6–7) in mass. Macrochemical reactions: KOH: rapidly slightly greenish and then yellow on pileus and stipe; yellowish on pileus context, stipe context, and hymenium. NH4OH: yellowish with greenish to purplish aura on the cap and stipe; yellowish on pileus context, stipe context, and hymenium. Basidiospores [172/3/2] (8.7–) 9.8–12–14.7 (–16.8) _ (3.1–)3.4–4 4.4 (–4.7) mm Q = (2.61–) 2.42–3.01–3.63 (–3.93). From the type (10.1–) 11.1–13.4–16.6 (–16.8) _ (3.6–) 3.7–4.1–4.6 (–4.7) mm, Q = (2.68–) 2.74–3.27–3.81 (–3.93), N = 57, narrowly ellipsoid to subcylindrical with slightly suprahilar depression, thin-walled, smooth, brownish to yellowish hyaline in water,
yellowish hyaline in KOH or NH4OH, inamyloid. Basidia 4-spored (19–) 19–22–25 (–25) _ (9–) 9–10–11 (11) mm, with sterigmata up to 4 mm long clavate, hyaline, inamyloid. Cheilocystidia (19–) 19–23–28 (–28) _ (6–) 6–8–10 (–10) mm, frequent, fusiform, thin-walled, hyaline. Pleurocystidia (34–) 35–40–47 (–47) _(5)5–6–7 (–7) mm, frequent, narrowly fusiform, thin-walled, hyaline. H. trama divergent to boletoid, 57–78 mm wide, with 18–42 mm wide of regular mediostratum. Pileipellis a tomentum to slightly gelatinized tomentum, 89–118 mm thick, composed of moderately interwoven, hyaline, thin-walled hyphae, with terminal cells 19–57 _ 5–8.5 mm, cylindrical with rounded apex, some hyphae were covered with mucus on the wall, at places with scattered of loose crystals. Pileus context made of strongly interwoven hyphae, 8.5–13 mm wide, at places with scattered of loose crystals. Stipitipellis hyphae vertically oriented (80–95 mm thick), pointing out of terminal cell 10–35 _ 4–12.5 mm of thin-walled with rounded apex, hyaline hyphae, giving rise to clusters of caulocystidia, which (23–) 23–27–35(–35) _ (7–) 7–10–13 (–13) mm, frequent in group, fusiform, thin-walled, hyaline, with somewhere scattered of loose crystals especially near the surface. Stipe context composed of parallel, 4.5- to 8-mm-wide hyphae, with scattered small loose crystals. Clamp connections not seen in any tissue. (Fig. 1G–K, 2)
Habitat: Solitary to gregarious, sometimes fasciculate, onsoil in dipterocarp forest dominated by D. obtusifolius, D. tuberculatus, Dipterocarpus intricatus, Sh. obtusa, and Sh. siamensis.
Distribution: Ubon Ratchathani Province, NortheasternThailand.
Specimens examined: THAILAND: Ubon Ratchathani Province: Trakan Phuet Phon District, Ban Huay Fai community forest, 15_32043.5800N–105_1001600E, elev. 160m, July 11, 2014, Santhiti Vadthanarat, SV0029 (CMUB, BR); –ibid., 15_32042”N–105_1001600E, elev. 175 m, July 24, 2016, Santhiti Vadthanarat, SV0313 (CMUB, BR); –ibid., 15_32042”N–105_1001600E, elev. 160 m, July 15, 2017, Santhiti Vadthanarat, SV0405 (CMUB, BR); –ibid., 15_32043”N–105_1001700E, elev. 160 m, July 15, 2017, Santhiti Vadthanarat, SV0407 (CMUB, BR); –ibid., 15_32043”N–105_1001500E, elev. 175 m, July 15, 2017, Santhiti Vadthanarat, SV0410 (CMUB, BR); Sri Suk Village, Khok Tam Lae community forest, 15_3504600N–105_0603500E, elev. 150 m, August 6, 2015, Santhiti Vadthanarat, SV0203 (CMUB, BR); Trakan Phuet Phon market, September 22, 2016, Santhiti Vadthanarat, SV0353 (CMUB, BR).
Notes: S. ubonensis is characterized by the combination of following characteristics: medium sized basidiomata, purplish gray when young becoming purplish to reddish brown with age; unchanged context; pileipellis a tomentum to slightly gelatinized tomentum, with cylindrical terminal elements with rounded apex; found in dipterocarp forest in Northeastern Thailand. Morphologically, S. ubonensis is superficially similar to S. eximius in macro-characters especially when young. Both species are also similar in some microscopic characters including the presence and shape of cheilocystidia, pleurocystidia, and caulocystidia, as well as the shape of elements on pileipellis. However, they are different in pileipellis structure, with S. eximius having a trichoderm, whereas S. ubonensis has a tomentum to slightly gelatinized tomentum. The two species also occur on different continents, with S. ubonensis being found in Ubon Ratchathani Province, Northeastern Thailand, Southeast Asia, whereas S. eximius is found in North America (Singer, 1947; Smith and Thiers, 1971; Halling et al., 2012). Phylogenetically, S. ubonensis (clade 7) was clusters in a poorly supported, long-branch, sister to S. obscuripellis (clade 8) from Chiang Mai Province, Thailand, and S. subrufus (clade 6) from China. However, these two species differ from S. ubonensis as follows: S. obscuripellis has smaller basidiomata and is also paler, especially when young; lacks pleurocystidia; and has a trichoderm pileipellis composed of slightly dark to dark hyphae, with cylindrical terminal cells with subacute to rounded apex. So far, S. obscuripellis has been found only in Chiang Mai Province. S. subrufus also has paler basidiomata; paler pores, especially when young, which are pale brown to brown to pale reddish brown; stipe surface and context turn reddish when injured; a trichoderm pileipellis, composed of rather vertically arranged, with clavate or subclavate terminal cells, with obtuse apex; found in the forests dominated by Fagaceae trees, including Lithocarpus spp. (Chai et al., 2019). So far, S. ubonensis is the only Sutorius species found in Ubon Ratchathani Province, Northeastern Thailand. It occurs in dry dipterocarp forest at the lowest elevation (about 150–175 m) compared to the other Sutorius species.
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)