Rostrupomyces sisongkhramensis (Khamsuntorn, Pinruan & Luangsa-ard) Vadthanarat, Raghoonundon & Raspe, 2024

Vadthanarat, Santhiti, Raghoonundon, Bhavesh, Lumyong, Saisamorn & Raspe, Olivier, 2024, Rostrupomyces, a new genus to accommodate Xerocomus sisongkhramensis, and a new Hemileccinum species (Xerocomoideae, Boletaceae) from Thailand, MycoKeys 103, pp. 129-165 : 129

Rostrupomyces sisongkhramensis (Khamsuntorn, Pinruan & Luangsa-ard) Vadthanarat, Raghoonundon & Raspe comb. nov.

Figs 3 , 4 , 5A-B

Xerocomus sisongkhramensis Khamsuntorn, Pinruan & Luangsa-ard. Basionym.

Diagnosis.

Rostrupomyces sisongkhramensis is characterised by having dark to reddish brown, becoming brown to grayish orange pileus, with rugulose to subrugulose, finely tomentose to tomentose surface; yellowish to orange white, subscabrous, longitudinally fissurate stipe surface, with moderately scattered brown to dark brown to reddish brown granulose squamules; yellow hymenophore; unchanging color in any parts; yellowish brown spore print; and broadly ellipsoid to ellipsoid smooth basidiospores.

Description.

Basidiomata medium-sized. Pileus 37-94(118) mm in diameter, convex at first then plano-convex to plane, sometimes with sub-depressed at the centre; margin inflexed at first then deflexed in age, exact or slightly exceeding (up to 1 mm); surface at first rugulose especially near the margin then subrugulose in age, dull, dry to moist, finely tomentose to tomentose covered with greenish yellow (3A3-4, 3B4) matted hyphae at places (especially when young), at first dark brown to reddish brown (6-8F4-8), becoming light brown to brown to grayish orange (6D/E5-6, 5B4-5) on light yellow to brownish orange (4A3-5, 5C4) background in age, gradually paler to the margin, unchanging when bruised; context (3)5-10(14) mm thick half-way to the margin, at first firm then soft in age, color distribution even, at first off-white, slightly brownish (7D/E4-5) near the pileipellis, then yellowish to orange white (4-5A2) or occasionally yellowish (3A3-4) above the hymenium especially in age, unchanging when cut. Stipe (33)41-97(108) × 6(7)-19(20) mm, central, terete, usually cylindrical for the most part but often with wider base, rarely club-shaped; surface subscabrous longitudinally fissurate, slightly shiny, yellowish white to pale yellow to orange white (3A3 to 4A2 to 5A2), occasionally pale yellow (3A3-4) near the cap, with moderately scattered brown to dark brown to reddish brown (7D/E/F4-7) granulose squamules, unchanging when bruised; basal mycelium little developed, white (1A1); context solid, firm, at first white (1A1) becoming off-white to yellowish white (4A2) occasionally pale yellow (3A3-4) especially in the above part near the stipe surface in age, yellowish to orange gray (4-5B2-3) virgate at places, unchanging when cut. Hymenophore tubulate, slightly depressed to depressed around the stipe, with slightly decurrent tooth, sometimes almost free, mostly segmentiform to subventricose. Tubes (3)4-13 mm long half-way to the margin, at first pale yellow (4A3) then grayish yellow (4B3) when mature, separable from the pileus context, unchanging when cut. Pores 0.2-0.8(1.3) mm wide half-way to the margin, irregularly arranged, roundish then subangular to angular in age; topography subregular, composite pores frequent; color distribution even, when young white (1A1) then yellowish white (4A2) becoming grayish yellow (4B3-5) infrequently with reddish brown spots (7-8E/F8) at places in age, unchanging when touched. Odour mild fungoid. Taste mild. Spore print yellowish brown (5F5) in mass.

Macrochemical reactions: KOH, brownish orange on pileus, yellowish to pale dull orange on pileus context and stipe surface, none or yellowish on stipe context, yellowish brown to brownish orange on hymenium; NH4OH, yellowish to brownish orange (occasionally with purple aura) on pileus, yellowish to pale orange on stipe surface, yellowish to brownish on hymenium, none or yellowish on pileus context and stipe context.

Spores [591/10/10] (6.3-)6.9-7.9-9.1(-9.8) × (4.5-)4.8-5.5-6.2(-6.5) µm Q = (1.2-)1.29-1.44-1.63(-1.79). From the type (6.5-)6.9-7.7-8.8(-9.5) × (4.7-)5-5.5-6.2(-6.5) µm, Q = (1.2-)1.25-1.41-1.54(-1.63), N = 106, broadly ellipsoid to ellipsoid, thin-walled, smooth under light microscope and SEM, yellowish hyaline in water or KOH, inamyloid. Basidia 4-spored, (22-)22-26-31(-31) × (9-)9-11-13(-13) µm, clavate without basal clamp connection, hyaline to yellowish hyaline in KOH; sterigmata up to 4 µm long. Cheilocystidia (30-)30-43-58(-59) × (9-)9-11-15(-15) µm, frequent, narrowly fusiform to fusiform with obtuse apex or narrowly utriform, thin-walled, hyaline in KOH. Pleurocystidia (33-)33-43-63(-63) × (8-)8-11-13(-13) µm, infrequent, narrowly fusiform to fusiform with obtuse apex, thin-walled, hyaline in KOH. Hymenophoral trama subregular to slightly divergent, 38-82 µm wide, with subregular mediostratum 8-24 µm wide, composed of cylindrical, 4-12 µm wide hyphae, hyaline in KOH. Pileipellis an intricate trichoderm, 70-130 mm thick, made of moderately interwoven (when young) to loosely interwoven in age, thin-walled, smooth, hyaline hyphae 4-18 mm wide, branching and anastomosing at places; terminal cells 12-65 × 4-18 mm, narrowly fusiform to fusiform to broadly fusiform with slightly acuminate or obtuse apex, hyaline to yellowish pale brown in KOH. Pileus context made of strongly interwoven, thin-walled hyphae, up to 12 µm wide, hyaline in KOH. Stipitipellis arranged parallel to the surface of the stipe, composed of moderately interwoven, cylindrical, thin-walled, 3-10 µm wide hyphae, anastomosing and branching at places, sparsely scattered with groups of rising cells to clusters (up to 87 µm high) of narrowly clavate to clavate cells (21-36 × 4-9 µm), hyaline to yellowish hyaline in KOH. Caulocystidia not seen. Stipe context parallelly arranged, composed of moderately interwoven, cylindrical, thin-walled, 3-18 µm wide hyphae, hyaline to yellowish hyaline in KOH. Clamp connections not seen in any tissue.

Habitat and distribution.

Solitary or in small groups (up to 4 basidiomata), or fasciculate by 2 to 3 basidiomata, on sandy loam to sandy clay loam soil in open dry dipterocarp forest and dipterocarp forest dominated by Dipterocarpaceae trees namely Anthoshorea roxburghii , Dipterocarpus obtusifolius , D. tuberculatus , D. intricatus , Pentacme siamensis , and Shorea obtusa with or without scattered Fagaceae trees. Currently known from the type locality (Nakhon Phanom province), Sisaket and Ubon Ratchathani provinces in northeastern Thailand, and also in Chiang Mai and Chiang Rai provinces in northern Thailand.

Specimens examined.

Thailand, Chiang Mai Province, Muang District, Doi Suthep-Pui National Park , 18°47'39.4"N, 98°55'21.5"E, elev. 915 m, 20 July 2015, Olivier Raspé, OR 1004 (CMUB, BKF, BR) ; ibid., 18°48'04.2"N, 98°55'44.3"E, elev. 775 m, 21 July 2015, Santhiti Vadthanarat, SV0155 (CMUB, BKF); Mae On District , 18°51'57.4"N, 99°17'22.9"E, elev. 660 m, 1 June 2015, Olivier Raspé, OR0915 (CMUB, BR) ; ibid., 18°51'57.0"N, 99°17'23.0"E, elev. 660 m, 1 June 2015, Olivier Raspé, OR0918 (CMUB, BR) ; ibid., 18°51'57.0"N, 99°17'23.0"E, elev. 660 m, 1 June 2015, Olivier Raspé, OR0919 (CMUB, BR) ; ibid., 18°52'13.0"N, 99°18'25.0"E, elev. 760 m, 15 August 2015, Santhiti Vadthanarat, SV0219 (CMUB, BR) ; ibid., 18°51'57.4"N, 99°17'22.0"E, elev. 700 m, 16 August 2015, Santhiti Vadthanarat, SV0225 (CMUB, BR) ; ibid., 18°51'57.7"N, 99°17'26.5"E, elev. 685 m, 1 June 2017, Santhiti Vadthanarat, SV0397 (CMUB, BR) ; ibid., 18°52'15.6"N, 99°18'11.5"E, elev. 800 m, 11 July 2017, Olivier Raspé, OR1392 (CMUB, BR) ; ibid., 18°52'15.6"N, 99°18'11.5"E, elev. 800 m, 11 July 2017, Olivier Raspé, OR1399 (CMUB, BR) ; ibid., 18°52'16.7"N, 99°18'13.0"E, elev. 800 m, 9 June 2021, Santhiti Vadthanarat, SV0512 (CMUB, BR) ; ibid. 18°52'7.9"N, 99°17'42.0"E, elev. 780 m, 10 June 2021, Santhiti Vadthanarat, SV0517 (CMUB, BR) ; ibid. 18°52'16.4"N, 99°17'40.5"E, elev. 820 m, 10 June 2021, Santhiti Vadthanarat, SV0518 (CMUB, BR) ; ibid. 18°52'12.0"N, 99°17'31.2"E, elev. 700 m, 10 June 2021, Bhavesh Raghoonundon, BR0311 ; ibid. 18°52'26.8"N, 99°18'15.5"E, elev. 845 m, 10 June 2021, Bhavesh Raghoonundon, BR0313 ; Chiang Rai Province, Phan District , 19°48'50.0"N, 99°51'57.0"E, elev. 730 m, 22 June 2021, Bhavesh Raghoonundon, BR0368 ; ibid. 19°48'50.0"N, 99°51'57.0"E, elev. 730 m, 22 June 2021, Bhavesh Raghoonundon, BR0371 ; Sisaket Province, Kanthararom District, Kok Yang Yai roadside market, 17 September 2016, Santhiti Vadthanarat, SV 0345 (CMUB) ; Ubon Ratchathani Province, Trakan Phuet Phon District, Huay Fai , 15°32'44.3"N, 105°10'17.4"E, elev. 165 m, 28 July 2015, Olivier Raspé, OR 1059 (CMUB, BR) .

ITS sequence accession number (SV0155): PP354891.

Notes.

The BLAST result based on ITS sequence obtained from one of the examined specimens (voucher SV0155, GenBank accession number PP354891) was 100% identical to the holotype of X. sisongkhramensis (voucher BBH 48255, accession number OP462477) which was reported by Tan et al. 2022. This suggested that our collections belonged to X. sisongkhramensis. Morphological characters of our collections mostly fit the original description of the species. However, some variations were observed between ours and the original description as follows: Tan et al. (2022) mentioned the absence of cheilocystidia in X. sisongkhramensis while we could observe them in our collections; they were narrowly fusiform to fusiform with obtuse apex or narrowly utriform, thin-walled. The protologue mentioned broadly clavate to subclavate (40-60 × 8-15 μm) caulocystidia. However, in our observation only groups of rising terminal cells of shape and size similar to the caulocystidia in Tan et al. (2022), were observed. What Tan et al. (2022) considered as caulocystidia were what we described as undifferentiated terminal cells of the stipitipellis. In the species protologue, the pileipellis and stipitipellis were described as composed of thick-walled hyphae (no measurement mentioned). However, only thin-walled hyphae were observed in our collections.

Rostrupomyces sisongkhramensis is morphologically similar to Hemileccinum duriusculum Mei-Xiang Li, Zhu L. Yang & G. Wu, which was recently described from China. The two species share some morphological characters including basidiome size and color, scattering of granular squamules on the stipe surface, pale yellow to grayish yellow hymenophore that is depressed around the stipe apex, and unchanging color in any parts. However, H. duriusculum differs by its strikingly venose pileus surface, finer granular squamules on the stipe surface, and subfusiform basidiospores ornamented with irregular warts under SEM ( Liu et al. 2024). Rostrupomyces sisongkhramensis is also somewhat similar to a European Leccinum species originally described from Italy, Leccinum albostipitatum den Bakker & Noordel., which has a similar shade of pileus color (light orange), whitish stipe covered with whitish squamules when young to reddish brown in age. However, L. albostipitatum can be differentiated by having an inflexed margin which exceeds the hymenophore by up to 4 mm, yellowish white to very pale brown hymenophore that becomes brownish when bruised, a clear blue discoloration of the stipe base when touched, context staining vinaceous then grayish to blackish when cut, smooth fusiform basidiospores, distribution in Europe, and association with Populus L. trees ( den Bakker and Noordeloos 2005).

Phylogenetically, R. sisongkhramensis is closely related to Rubinosporus auriporus Vadthanarat, Raspé & Lumyong, the only known species in the genus, which was described from the same region as Rostrupomyces (northern Thailand). However, it can be differentiated from R. sisongkhramensis by having grayish red to pastel red to reddish brown pileus; even stipe surface with scattered bright yellow to yellowish white to orange to light brown minute squamules; shorter tubes especially when young; golden yellow hymenophore; and the striking dark ruby spore print ( Vadthanarat et al. 2022).

Figures

Figure 3. Fresh basidiomata of Rostrupomyces sisongkhramensis A OR 0915 B OR 0919 C OR 1004 D SV 0155, white pores surface in young basidioma (white arrow) E SV 0219 F SV 0225. Scale bars: 1 cm (A-F).

Figure 4. Microscopic features of Rostrupomyces sisongkhramensis A basidiospores B basidia C cheilocystidia D pleurocystidia E pileipellis F stipitipellis showing a cluster of narrowly clavate to clavate cells which slightly scattered on the stipe surface. Scale bars: 10 µm (A-D); 25 µm (D-E); 50 µm (E-F). All line drawings were made from SV 0155.

Figure 5. Scanning electron micrographs of basidiospores A-B Rostrupomyces sisongkhramensis (SV 0155) C-D Hemileccinum inferius (SV 0282).