Rubinosporus auriporus Vadthanarat, Raspé & Lumyong
MycoBank number: MB840263
Basidiomata medium-sized. Pileus (14–)33–92(–174) mm in diameter, hemispherical at first then convex to plano-convex or applanate in age; margin inflexed to deflexed, exact to slightly exceeding somewhere (0.5 mm); surface even to subrugulose at places, dull, greyish red to pastel red to reddish-brown (8E5–6, 9B/C/D5–7, 9E6), at first densely to moderately covered with greyish yellow, greyish orange to brownish orange to brown (4B3–5, 5B3–5, 5C3–6, 5D3–4, 6E7–8) matted, cracked tomentum becoming less in age; context 4–15 mm thick half-way to the margin, firm, off-white to yellowish-white (1A1–2), occasionally pale yellow (1A2–3) above the hymenium or under pileipellis, unchanging when cut. Stipe 37–109 × 11–45 mm, central, terete or slightly compressed sometimes, mostly cylindrical to cylindrical with slightly wider base; surface topography even, slightly shiny, yellowish-white (2A2–3, 3A2) with pinkish white (8A2) at places, scattered with yellowish-white (2A2–3, 3A2) to orange to light brown (5A/B7, 7D7–8) minute squamules, to bright yellow (2–3A7) near the top; basal mycelium little developed, yellowish-white (2A2); context solid, off-white to yellowish-white (1A1–2), even to virgate at places, unchanging when cut. Hymenophore tubulate, narrowly adnate, mostly segmen tiform to subventricose. Tubes (0.8)2–4.5(7) mm long half-way to the margin, relatively thin when young 1/4 to 1/5 times then 1/2 to 1/3 times that of the pileus context when mature, golden yellow (3A7) becoming orange-yellow (4B7), separable from the pileus context, unchanging when bruised. Pores 0.4–0.8(1) mm wide at mid-radius, topography subirregular, irregularly arranged, composite pores composed of roundish to slightly angular pores in age, golden yellow (3–4A8) at first, golden yellow to greyish yellow (4A/B/C7) with irregularly reddish brown (8E/F8) at places in age, unchanging when touched. Odor mild fungoid. Taste mild to slightly sweet. Spore print dark ruby (12F7) in mass. Macrochemical reactions: KOH, yellow to orange on cap, stipe, and hymenium; none or yellowish on pileus context and stipe context; NH4OH, yellow to orange to brown on cap, stipe and hymenophore; none or yellowish on pileus context, stipe context and hymenium. Spores [293/5/2] (6.5–)7.1–7.9–8.7(–9.3) × (4.4–)5.2–5.8–6.4(–6.9) µm Q = (1.19–)1.25–1.36–1.52(–1.68). From the type (7–)7.1–7.7–8.6(–9) × (4.4–)4.8–5.7–6.5(–6.8) µm, Q = (1.19–)1.23–1.36–1.53(–1.66), N = 60, broadly ellipsoid, thin-walled, smooth, yellowish to brownish hyaline in water, yellowish hyaline in KOH or NH4OH, yellowish to reddish in Melzer’s reagent (inamyloid to weakly dextrinoid). Basidia 4-spored, (18–)19–24–27(–28) × (9–)9–11–12(–12) µm, clavate without basal clamp connection, hyaline to yellowish hyaline in KOH or NH4OH; sterigmata up to 4 _m long. Cheilocystidia of two types, (1) clavate with rounded apex, frequent, (14–)15–25–36(–38) × (9–)10–12–16(–16) µm, thin-walled, hyaline to yellowish hyaline in KOH or NH4OH, and (2) fusiform to broadly fusiform or utriform, frequent, (21–)22–34–41(–41) × (10–)10–12–15(–16) µm, thin-walled, hyaline to yellowish hyaline in KOH or NH4OH. Pleurocystidia (29–)30–47–58(–61) × (9–)9–12–16(–18) µm, frequent and more near the pores, fusiform with narrower apex, thin-walled, hyaline to yellowish hyaline in KOH or NH4OH. Hymenophoral trama divergent, 57–106 µm wide, with 16–32 µm wide of subregular mediostratum, composed of cylindrical, 4–12 µm wide hyphae, slightly yellowish to hyaline in KOH or NH4OH. Pileipellis a tomentum to intricate trichoderm, 125–230 µm thick, composed of moderately interwoven thin-walled hyphae; terminal cells 21–68 × 3.5–9 µm, cylindrical with obtuse apex, hyaline to yellowish at places in KOH. Pileus context made of strongly interwoven, thin-walled, hyaline hyphae, 7–23 µm wide, hyaline in KOH. Stipitipellis a tomentum composed of loosely to moderately interwoven cylindrical hyphae (3–9 µm wide), anastomosing at places, scattered with groups of rising cells to clusters of basidiole-like cells ((14–)15–23–38(–39) × (5–)6–8–10(–11) µm) mixed with two types of caulocystidia, and rarely with caulobasidia, 120–170 µm thick (including the height of rising cells), hyaline to yellowish hyaline in KOH or NH4OH; terminal cells 24–81 × 5–9 µm, more or less parallel to the surface of the stipe, thin-walled, elongated cylindrical with obtuse to slightly swollen apex. Caulocystidia of two types, 1) fusiform, not frequent, (25–)26–45–72(–76) × (9–)9–14–18(–18) µm, thin-walled, hyaline to yellowish hyaline in KOH, and 2) broadly clavate, not frequent, (14–)14–23–34(–34) × (10–)10–15–21(–21) µm, thin-walled, hyaline to yellowish hyaline in KOH. Stipe context composed of parallel, 6–18(23) µm wide hyphae, hyaline to yellowish hyaline in KOH or NH4OH. Clamp connections were not seen in any tissue.
Habitat and distribution: Gregarious (up to 6 basidiomata) to fasciculate of 2–4 basidiomata, on soil in hill evergreen forest dominated by Fagaceae mixed with Dipterocarpaceae: Dipterocarpus obtusifolius, D. costatus, Shorea siamensis, Hopea sp. Currently known only from the type locality in Chiang Mai Province, northern Thailand.
Specimens examined:THAILAND, ChiangMai Province,Mae Taeng District, 19_06032.0 0 N–98_44033.0 0 E, elev. 1,070 m, 4 Jun 2015, Santhiti Vadthanarat, SV0101 (CMUB, BR); ibid.19_06033.80 0 N–98_44020.90 0 E, elev. 1110 m, 23 May 2017, Santhiti Vadthanarat, SV0394 (CMUB, BR); ibid. 19_06036.20 0 N–98_44041.10 0 E, elev. 1080 m, 23 May 2017, Santhiti Vadthanarat, SV0396 (CMUB, BR).
Notes: In the new species, the hymenophoral cystidia contained greenish yellow (1A8) pigments when fresh specimens were observed in water under a compound microscope. However, the pigment was discolored when the cystidia were observed in KOH or NH4OH, or after treatment of the specimen with heat (drying at 45–50 _C). A macro-morphologically similar species, Butyriboletus roseoflavus (Hai B. Li & Hai L.Wei) D. Arora & J.L. Frank originally described from China, has a similar color tone of basidiomata with a light pink, light purplish red to rose-red pileus; and lemon-yellow, oliveyellow or honey-yellow hymenophore. However, it can be differentiated from R. auriporus by having a yellower and reticulated stipe which is lemon-yellow or light yellow with almost entirely reticulate stipe or at least in lower part; yellower context which is lemon-yellow and also variable staining reaction in response to bruising, bruising blue slowly or unchanging; bruising blue promptly hymenophore; subfusiform basidiospores; olive brown spore deposit; and the habitat in Pinus or mixed forests dominated by Pinus. The chemical reaction of basidiospores with Melzer’s reagent which was negative to weakly dextrinoid in R. auriporus is also present in two Xerocomoideae species, Alessioporus ichnusanus (Alessio, Galli & Littini) Gelardi, Vizzini & Simonini, and Pulchroboletus roseoalbidus (Alessio & Littini) Gelardi, Vizzini & Simonini. However, the two species are different from R. auriporus by their basidiospore shapes, which are sub-cylindrical or ellipsoid or ellipsoid-fusoid, the strong discoloration (bluing or darkening) in parts of basidiomata, and olive-brown spore deposit.