Refers to the dark, chocolate brown hymenophore and overall colour of basidiomata.

Similar to the genus Sutorius in having brown basidiomata with brown encrustations in the flesh but differs from Sutorius in having the following combination of characters: brown to chocolate brown or greyish-brown to dark brown or blackish-brown basidiomata, without violet tinge, chocolate brown to dark brown hymenophore, tubes not separable from the pileus context, white to off-white basal mycelium which turns reddish-white to pale red when bruised, amygdaliform to ovoid with subacute apex in side view to ovoid basidiospores and dark brown spore deposit.

Basidiomata stipitate-pileate with poroid hymenophore, small to medium-sized, dull, brown to greyish-brown to dark brown or blackish-brown. Pileus convex when young becoming plano-convex to slightly depressed with age, with deflexed to inflexed margin; surface even to subrugulose, minutely tomentose or slightly cracked at the centre; context soft, yellowish to greyish off-white then slightly greyish-orange to dull orange to greyish-brown when exposed to the air, patchy or marmorated with greyish-brown to dark brown, sometimes with scattered small dark brown to brownish-black encrustations, not or inconsistently reddening when cut. Hymenophore tubulate, adnate, subventricose to ventricose, slightly depressed around the stipe; tubes brown to greyish-brown to dark brown, not separable from the pileus context; pores regularly arranged, mostly roundish at first becoming slightly angular with age, sometimes irregular, elongated around the stipe, dark brown to greyish-brown at first, becoming brown to chocolate brown with age. Stipe central, terete to sometimes slightly compressed, cylindrical to sometimes slightly wider at the base; surface even, minutely tomentose, dull, dark brown to greyish-brown, basal mycelium white to off-white becoming reddish-white to pale red when touched; context solid, yellowish to orange white to yellowish-grey to pale orange to dull orange to reddish-grey, marmorated or virgated with brownish-grey to greyish-brown to dark brown, sometimes scattered with small reddish-brown to brownish-black fine encrustations, unchanged or inconsistently reddening when cut. Spore print dark brown.

Basidiospores amygdaliform to ovoid or ovoid with subacute apex in side view, thin-walled, smooth, slightly reddish to brownish hyaline in water, slightly yellowish to greenish hyaline in KOH or NH₄OH, inamyloid. Basidia 4-spored, clavate to narrowly clavate without basal clamp connection. Cheilocystidia fusiform or cylindrical with obtuse apex, sometimes bent or sinuate, thin-walled, often scattered with small brownish-yellow to yellowish-brown crystals on the walls in KOH or NH₄OH. Pleurocystidia narrowly fusiform with obtuse apex or cylindrical to narrowly subclavate, sometimes bent or sinuate, thin-walled, densely covered with small reddish-brown to brownish dark encrustations on the walls when observed in H₂O, which are discoloured then dissolved in KOH or NH₄OH. Pileipellis a trichoderm becoming tangled trichoderm to tomentum, composed of thin-walled hyphae; terminal cells mostly slightly sinuate cylindrical to irregular with rounded apex or clavate to elongated clavate. Stipitipellis a trichoderm to tangled trichoderm or disrupted hymeniderm, composed of loosely to moderately interwoven cylindrical hyphae anastomosing at places. Clamp connections not seen in any tissue.

Cacaoporus tenebrosus

Currently known from Thailand.

Sutorius most closely resembles the new genus. In the field, Cacaoporus is easily distinguished from the Sutorius by the following combination of characters: chocolate brown to dark brown to blackish-brown basidiomata, which are darker than in Sutorius and never purplish-brown like in Sutorius species; chocolate brown to dark brown hymenophore, which is much darker than in Sutorius and never reddish- to purplish-brown like in Sutorius; tubes that are not separable from the pileus context but can be separated in Sutorius; off-white basal mycelium that more or less turns red when bruised, which is never the case in Sutorius.

Refers to the context, which is paler than in the other species, especially at the stipe base and in the pileus.

THAILAND, Chiang Mai Province, Mae On District, 18°52'37"N, 99°18'23"E, elev. 860 m, 15 August 2015, Santhiti Vadthanarat, SV0221 (CMUB!, isotype BR!).

Cacaoporus pallidicarneus is characterised by having a paler context than the other species and basidiospores that are amygdaliform or elongated amygdaliform to ovoid in side view, sometimes with subacute apex, shorter basidia and fusiform to narrowly bent fusiform to narrowly fusiform hymenophoral cystidia.

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 off-white 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; NH₄OH, 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 NH₄OH, 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 NH₄OH; 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 NH₄OH. 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 NH₄OH. 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 NH₄OH. 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 NH₄OH. 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 NH₄OH 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 NH₄OH. Stipe context composed of parallel, 3–7 µm wide hyphae, brownish hyaline to yellowish pale brown in KOH or NH₄OH. Clamp connections not seen in any tissue.

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.

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.

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 are 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.

Figure 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).

Refers to the overall darkness of basidiomata, including the context.

THAILAND, Chiang Mai Province, Mae On District, 18°52'37"N, 99°18'32"E, elev. 940 m, 15 August 2015, Santhiti Vadthanarat, SV0223 (holotype CMUB!, isotype BR!).

Cacaoporus tenebrosus is characterised by having a darker context than the other species, longer basidia and cylindrical to narrowly subclavate hymenophoral cystidia.

Basidiomata medium-sized. Pileus (2.3)3.1–5(9) cm in diameter, convex when young becoming plano-convex to slightly depressed with age; margin inflexed to deflexed, slightly exceeding (1–2 mm); surface even to subrugulose, minutely tomentose, slightly cracked at the centre, dull, greyish-brown (10F3) to dark brown to blackish-brown (8F4–5) to the margin; context 5–10 mm thick half-way to the margin, soft, marmorated, greyish-brown to dark brown (10F3–5) with greyish-brown (9B/D3), scattered with reddish-brown to brownish-black, fine encrustations at places, slightly reddening in paler spots when cut. Stipe central, terete, cylindrical to sometimes with slightly wider base, 4.3–7.0 × 0.7–1.4 cm, surface even, minutely tomentose, dull, dark brown to greyish-brown (9F4 to 10F3), basal mycelium white to off-white becoming reddish-white to pale red (7A3–4) when bruised; context solid, greyish-brown to dark brown (9–10F3–5) marmorated with reddish-grey (7/10B2), usually scattered with small reddish-brown to brownish-black fine encrustations, slightly reddening when cut. Hymenophore tubulate, adnate, subventricose to ventricose, slightly depressed around the stipe. Tubes (4)7–13 mm long half-way to the margin, brown to dark brown (8F3 to 9F4), not separable from the pileus context. Pores 0.8–2 mm wide at mid-radius, regularly arranged, mostly roundish at first, becoming slightly angular with age, sometime irregular, elongated around the stipe; colour distribution even, greyish-brown to dark brown (9F4) at first, becoming chocolate brown to brown (10F3 to 7–8F4–5) with age. Odour mild fungoid. Taste slightly bitter at first, then mild. Spore print dark brown (8/9F4) in mass.

Macrochemical reactions. KOH, yellowish then brown to black on cap, stipe, pileus context, stipe context and hymenium; NH₄OH, yellowish then orange to brown on cap, stipe, pileus context, stipe context and hymenium.

Basidiospores [290/8/6] (7.4–)7.7–8.4–9.2(–10) × (4.5–)5–5.3–5.7(–6.1) µm Q = (1.25–)1.44–1.57–1.77(–2). From the type (2 basidiomata, N = 134) (7.5–)7.7–8.2–9(–9.9) × (4.9–)5–5.4–5.7(–5.9) µm, Q = (1.41–)1.43–1.54–1.71(–1.9), ovoid, thin-walled, smooth, slightly reddish to brownish hyaline in water, slightly yellowish to greenish hyaline in KOH or NH₄OH, inamyloid. Basidia 4-spored, (33.6–)34.3–38.8–45.8(–47) × (7.7–)7.8–9.5–10.8(–10.9) µm, clavate to narrowly clavate without basal clamp connection, yellowish to brownish hyaline to slightly dark in KOH or NH₄OH; sterigmata up to 5 µm long. Cheilocystidia (22–)22.1–28.7–37(–37) × (3–)3.1–4.4–5(–5) µm, frequent, cylindrical with obtuse apex, sometimes bent or sinuate, thin-walled, yellowish-brown to dark brown in KOH or NH₄OH, often scattered with small brownish-yellow to yellowish-brown crystals on the walls in KOH or NH₄OH. Pleurocystidia (62–)62.5–81.5–99(–99) × (7–)7–8–9(–9) µm, frequent, cylindrical to narrowly subclavate, sometimes bent or sinuate, thin-walled, with yellowish-brown to slightly dark content in KOH or NH₄OH, densely covered with small reddish-brown to brownish dark encrustations on the walls when observed in H₂O, with some scattered small brownish-yellow to yellowish-brown crystals on the walls in KOH or NH₄OH. Hymenophoral trama subdivergent to divergent, 80–170 µm wide, with 60–80 µm wide of subregular mediostratum, composed of cylindrical, 4–8(11) µm wide hyphae, slightly yellowish to brownish hyaline in KOH or NH₄OH. Pileipellis a tangled trichoderm to tomentum at places, 70–110 µm thick, composed of moderately interwoven thin-walled hyphae; terminal cells 12–48 × 4–7 µm mostly slightly sinuate, cylindrical to irregular with rounded apex, at places clavate to elongated clavate terminal cells 18–33 × 7–9 µm, slightly dark to reddish to brownish dark in water, yellowish-brown to slightly dark in KOH or NH₄OH, scattered with small brownish-yellow to yellowish-brown crystals on the walls in KOH or NH₄OH. Pileus context made of moderately interwoven, thin-walled, hyaline hyphae, 7–12 µm wide. Stipitipellis a trichoderm to tangled trichoderm, 70–120 µm thick, composed of loosely to moderately interwoven cylindrical hyphae anastomosing at places, brownish dark to dark in KOH or NH₄OH. Caulocystidia (17–)17.6–29.4–46.3(–47) × (4–)4.1–5.5–6.9(–7) µm, clavate to cylindrical with obtuse apex, thin-walled, yellowish to brownish dark in KOH or NH₄OH. Stipe context composed of parallel, 4–6(12) µm wide hyphae, brownish hyaline to yellowish pale brown in KOH or NH₄OH. Clamp connections not seen in any tissue.

Gregarious (up to 9 basidiomata) to fasciculate or solitary, 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., Shorea spp. with a few Lithocarpus sp., Castanopsis sp. and Quercus sp. Currently known only from Chiang Mai Province, Northern Thailand.

THAILAND, Chiang Mai Province, Mae Taeng District, 19°07'15"N, 98°43'55"E, elev. 910 m, 29 July 2013, Olivier Raspé & Benjarong Thongbai, OR0654; ibid. 19°7'29"N, 98°40'59"E, elev. 1010 m, 24 May 2018, Santhiti Vadthanarat, SV0422; Mae On District, 18°52'37"N, 99°18'19"E, elev. 850 m, 15 August 2015, Santhiti Vadthanarat, SV0224; ibid., 18°52'35"N, 99°18'16"E, elev. 860 m, 15 July 2017, Olivier Raspé , OR1435; ibid., 6 June 2018, Santhiti Vadthanarat, SV0452.

There were many small yellowish to reddish to dark brownish particles or crystals on the walls of pileipellis, stipitipellis and hymenium cells, especially on the cystidia and basidia when observed in water. The small particles or crystals are somewhat dissolved and discoloured in KOH.

Microscopically, Cacaoporus tenebrosus differs from C. pallidicarneus by having a darker context, longer basidia (33.6–47 µm vs. 25.3–33.8 µm, respectively), longer and larger hymenophoral cystidia, which also differ in shape (cylindrical to narrowly subclavate in C. tenebrosus but fusiform to narrowly fusiform in C. pallidicarneus). Phylogenetically, all Cacaoporus collections with a dark context formed a clade sister to C. pallidicarneus (BS = 85% and PP = 0.88), but some (SV0224 and SV0422) were genetically somewhat distant from the other collections. However, we could not find any difference in morphology. Consequently, we consider them as the same species (C. tenebrosus). Study of more collections is needed to confirm or infirm that they belong to the same species.

Figure 3. 

Close-ups of hymenium/pileus context transition zone in Cacaoporus species, illustrating the non-separability of both tissues a C. pallidicarneus (OR0681) b C. tenebrosus (OR0654) c C. tenebrosus (SV0452). The transition between both tissues is particularly unmarked in C. pallidicarneus (a) Scale bars: 3 mm (a); 5 mm (b–c).

Figure 4. 

Scanning electron micrographs of Cacaoporus basidiospores a C. pallidicarneus (SV0221) b C. tenebrosus (SV0223). Scale bars: 1 µm (a–b).

Figure 5. 

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).

Figure 6. 

Microscopic features of Cacaoporus tenebrosus 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 (SV0223).