Mycrobank number: MB829657
Basidiomata small to medium-sized. Pileus (1.6)2.4–5.5 cm in diameter, convex when young becoming plano-convex with age; margin deflexed to inflexed, slightly exceeding (1–2 mm), surface even to subrugulose, minutely tomentose, dull, at first brown to greyish-brown to blackish-brown (8F3–4) sometimes paler (8C2) at places, becoming paler to greyish-brown (8E3–5) with age; context 4–9 mm thick half-way to the margin, soft, yellowish to greyish off-white then slightly pale orange to greyish-orange (6A3 to 6B3) when exposed to the air, with patchy or marmorated with greyish-brown (8E3) especially when young, scattered with reddish-brown to brownish-black of fine encrustations at places, slightly reddening when cut. Stipe central, terete or sometimes slightly compressed, cylindrical with slightly wider base, (2.0)2.8–3.7 × 0.4–0.7 cm, surface even, minutely tomentose, dull, greyish-brown to dark brown (8 E/F 3–4 to 8F2), basal mycelium white to offwhite becoming pale red (7A3) when bruised; context solid, yellowish to greyish off- white then orange white to pale orange (5A2–3) when exposed to the air, virgate to marmorate with brownish-grey (8F2), less so at the stipe base, at places scattered with brownish-black fine encrustations, unchanged to slowly slightly reddening when cut. Hymenophore tubulate, adnate, subventricose, slightly depressed around the stipe. Tubes (2)4–6 mm long half-way to the margin, brown to greyish-brown (8F3), not separable from the pileus context. Pores 0.4–1.5 mm wide at mid-radius, regularly arranged, mostly roundish to elliptical at first, becoming slightly angular with age, slightly elongated around the stipe, colour distribution even, dark brown to chocolate brown (9F4 to 10F3) at first, becoming chocolate brown to brown (10F4 to 7–8F4–5) with age. Odour rubbery. Taste slightly bitter at first, then mild. Spore print dark brown (8F4/5) in mass.
Macrochemical reactions. KOH, orange brown on cap, yellowish-black on stipe, yellowish-black on the pileus context and stipe context, brownish-black on hymenium; NH4 OH, yellowish-brown on cap, yellowish-orange on stipe, orangey yellow to yellowish-orange on the pileus context, stipe context and hymenium.
Basidiospores [437/7/5] (6.5–)6.7–7.7–8.6(–11.5) × (3.8–)4–4.6–5.1(–5.5) µm Q = (1.4–)1.48–1.68–1.9(–2.44). From the type (3 basidiomata, N = 177) (6.8– )7–7.8–8.5(–9.1) × (4–)4.2–4.6–5(–5) µm, Q = (1.49–)1.5–1.69–1.9(–2.21), amygdaliform or elongated amygdaliform sometimes to ovoid with subacute apex in side view, ovoid in front view, thin-walled, smooth, slightly reddish to brownish hyaline in water, slightly yellowish to greenish hyaline in KOH or NH4 OH, inamyloid. Basidia 4-spored, (25.3–)25.4–29.7–33.8(–33.8) × (7.3–)7.3–8.4–9.8(–10) µm, clavate without basal clamp connection, slightly yellowish to brownish hyaline in KOH or NH4 OH; sterigmata up to 5 µm long. Cheilocystidia (16–)16.3–23.4–32.8(–34) × (5.5–)5.8–7.3–9(–9) µm, frequent, fusiform, thin-walled, yellowish to brownish hyaline to brown in KOH or NH4 OH. Pleurocystidia (44–)44.2–54.7–67.6(–68) × (5–)5–6–7(–7) µm, frequent, usually narrowly bent fusiform to narrowly fusiform with obtuse apex, thin-walled, yellowish to brownish hyaline in KOH or NH4 OH. Hymenophoral trama subdivergent to divergent, 62–175 µm wide, with 25–100 µm wide, regular to subregular mediostratum, composed of cylindrical, 4–7(11) µm wide hyphae, yellowish to brownish hyaline in KOH or NH4 OH. Pileipellis a trichoderm to tangled trichoderm at first, becoming a tomentum to tangled trichoderm with age, 65–110 µm thick, composed of firmly to moderately interwoven thin-walled hyphae; terminal cells 12–55 × 4–6 µm, slightly bent cylindrical with rounded apex, at places clavate to sub-clavate to elongated clavate, 16–34 × 8–10 µm, slightly dark to reddish to brownish dark in water, yellowish to brownish hyaline to yellowish-brown to slightly dark at places in KOH or NH4 OH. Pileus context made of moderately interwoven, thin-walled, hyaline hyphae, 6–12 µm wide. Stipitipellis a disrupted hymeniderm, 55–95 µm thick, composed clavate cells, 11–37 × 5–8 µm, yellowish-brown to slightly dark in KOH or NH4 OH mixed with caulocystidia. Caulocystidia (17–)17–23.6– 31(–31) × (5–)5–6.3–7(–7) µm, frequent, thin-walled, mostly yellowish-brown to slightly dark at places in KOH or NH4 OH. Stipe context composed of parallel, 3–7 µm wide hyphae, brownish hyaline to yellowish pale brown in KOH or NH4 OH. Clamp connections not seen in any tissue.
Habitat and Distribution: solitary to gregarious up to 4 basidiomata, on soil in hill evergreen forest dominated by Fagaceae trees, with a few Dipterocarpus spp. and Shorea spp. or in Dipterocarp forest dominated by Dipterocarpus spp. and Shorea spp. with a few Lithocarpus sp., Castanopsis sp. and Quercus sp. Currently known only from Chiang Mai Province, Northern Thailand.
Specimens examined: THAILAND, Chiang Mai Province, Mae Taeng District, 23 km marker (Ban Tapa), 19°08'50"N, 98°46'50"E, elev. 930 m, 2 August 2013, Olivier Raspé & Anan Thawthong, OR0681; Ban Mae Sae, 19°14'70"N, 98°38'70"E, elev. 960 m, 3 August 2013, Olivier Raspé & Anan Thawthong, OR0683; Muang District, Doi Suthep-Pui National Park, 18°48'37"N, 98°53'33"E, elev. 1460 m, 14 July 2016, Olivier Raspé, OR1306; Mae On District, 18°52'35"N, 99°18'16"E, elev. 860 m, 6 June 2018, Santhiti Vadthanarat, SV0451.
Notes: We observed some small yellowish to reddish to brownish dark particles or crystals covering the cell walls in pileipellis, stipitipellis and on the hymenium, especially the cystidia and basidia when observed in water. The small particles or crystals were mostly dissolved in KOH. Cacaoporus pallidicarneus differs from C. tenebrosus by its basidiomata context colour which is paler, especially at the stipe base. A combination of the following characters is also distinctive: spore shape which is amygdaliform or elongated amygdaliform or sometimes ovoid with subacute apex in side view and ovoid in front view, while C. tenebrosus has ovoid spores, shorter basidia and differently shaped hymenophoral cystidia (see note under C. tenebrosus). Cacaoporus pallidicarneus has a stipitipellis which is a disrupted hymeniderm composed of caulocystidia and clavate cells, while the other species has a loose trichoderm or tangled trichoderm. Interestingly, one collection (SV0402) had a slightly paler context than C. tenebrosus but not as pale as C. pallidicarneus. The phylogenetic analyses indicated that this collection might be a species different from C. pallidicarneus and C. tenebrosus. However, the specimen was immature and, therefore, more collections are needed before the species can be formally recognised.
Fig. 1 Phylogenetic tree inferred from the four-gene dataset (atp6, cox3, rpb2 and tef1), including Cacaoporus species and selected Boletaceae using Maximum Likelihood and Bayesian Inference meth-ods (ML tree is presented). The two Buchwaldoboletus and nine Chalciporus species in subfamily Chal-ciporoideae were used as outgroup. Most of the taxa not belonging to the Pulveroboletus group were collapsed into subfamilies. All genera clades in Pulveroboletus group that were highly supported were also collapsed. Bootstrap support values (BS ≥ 70%) and posterior probabilities (PP ≥ 0.90) are shown above the supported branches.
Fig. 2 Habit of Cacaoporus species. a C. pallidicarneus (SV0221) b–d C. tenebrosus (b - SV0223, c - SV0224, d - SV0422). Scale bars: 1 cm (a–d).
Fig. 3 Microscopic features of Cacaoporus pallidicarneus a basidiospores b basidia c cheilocystidia d pleurocystidia e caulocystidia f pileipellis g stipitipellis. Scale bars: 10 µm (a–b); 25 µm (c–e); 50 µm (f–g). All drawings were made from the type (SV0221).
Vadthanarat, S., Lumyong, S. and Raspé, O., 2019. Cacaoporus, a new Boletaceae genus, with two new species from Thailand. MycoKeys, 54, p.1.