Sutorius mucosus Vadthanarat, Raspé and Lumyong sp. nov.
Basidiomata medium-sized. Pileus 9 cm in diameter, planoconvex with straight margin, margin slightly exceeding (1 mm); surface subrugulose, dull, waxy to subviscid, almost smooth to minutely tomentose under the lens, reddish brown (8E/F8). Pileus context 8–10 mm halfway to the margin, soft, dull yellowish white (4A2), with scattered small groups of reddish brown (9F5–7) encrustations, slightly reddening (5A2–3) when cut. Stipe central, terete, cylindrical, × 1.2 cm; surface subscabrous, with granulose squamules, purplish brown to dark brown (10–11F4–7), uplifted by pale brown (5B/C3– 5) hyphae; stipe context solid, slightly turgid, beige (4B/C3). Hymenophore tubulose, ventricose; tubes easily separable, pale orange (5A2–3), 7–9 mm long halfway to the margin; pores 0.2–0.3(0.5) mm wide at midradius, roundish to angular near the stipe, pore topography irregular, brown to brownish gray (7B4–5 to 8D/E4). Odor and taste not observed. Spore print reddish brown (8E/F8). Macrochemical reactions: KOH: yellowish on pileus context. Basidiospores (10.4–) 10.8–13.8–15 (–15.4) × (4.3–) 4.6–5– 5.5 (–5.6) µm, Q = (2.24–) 2.47–2.76–3.04 (–3.06), N = 55, narrowly ellipsoid to subcylindrical with slight suprahilar depression, thin-walled, smooth, brownish to yellowish hyaline in water, yellowish hyaline in KOH or NH4OH, inamyloid. Basidia 4-spored (23–) 23–26–30 (–30) × (10–) 10–11–13 (–13) µm, with sterigmata up to 4 µm long, clavate, hyaline, inamyloid. Cheilocystidia and Pleurocystidia not seen. H. trama slightly divergent to boletoid 17–42 µm wide, with subregular mediostratum 7–12 µm wide. Pileipellis an ixotrichoderm, 75– 125 µm thick, made of moderately interwoven, gelatinized, hyaline hyphae, with terminal cells 11–37 × 7–11 µm, fusiform to utriform with rounded to tapping apex, pale yellowish to brownish hyaline in water, mostly hyaline to yellowish hyaline in KOH or NH4OH, with scattered loose crystals. Pileus context composed of strongly gelatinized hyaline hyphae 8–16 µm wide, at places with scattered loose crystals. Stipitipellis a disrupted hymeniderm 200–450 (600) µm thick composed of parallel hyphae, with terminal cell 15–29 × 6– 9 µm of thin-walled, hyaline hyphae, giving rise to clusters of basidiole-like cells and caulocystidia, with scattered loose crystals. Caulocystidia (19–) 19–27–36 (–36) × (8–) 8–11–15 (–15) µm, not frequent, fusiform to broadly fusiform, thinwalled, hyaline. Stipe context composed of parallel, 8- to 12- µm-wide gelatinized hyphae, somewhere covered with some encrustations on the wall, with scattered loose crystals. Clamp connections not seen. (Fig. 2 d–g; Fig. 3)
Habitat: Solitary on soil in evergreen hill forest dominated by Castanopsis spp., Lithocarpus spp. mixed with D. obtusifolius, Dipterocarpus costatus, Sh. obtusa, and Sh. siamensis.
Distribution: Chiang Mai Province, Northern Thailand.
Notes: S. mucosus description is based on a single collection (OR0851); however, the strongly gelatinized pileipellis is a strikingly unique character, which, together with the phylogenetic evidence, which resolved this specimen as an isolated branch, within the Sutorius lineage, supports our interpretation of OR0851 as a new, distinct species. Other important characters that allow differentiating S. mucosus are the fusiform to utriform pileipellis terminal cells with rounded to subacute apex and the lack of cheilocystidia and pleurocystidia.
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)