Boletales » Boletaceae » Retiboletus

Retiboletus brevibasidiatus

Retiboletus brevibasidiatus Raspé & Chuankid

MycoBank no.: MB 835032, Faces of Fungi FoF 07863.

Basidiomata medium-sized. Pileus 43–88 mm diam, convex when young, subhemispherical to convex when aged, densely subtomentose; surface dry, dark blonde to clay (5D4–5) or hair brown to bronze (5E4–5) with brownish grey (6F8) patches; margin inflexed when young, then straight to slightly reflexed, abruptly paler than the rest of the pileus, at least in immature basidiomes; context 9–11 mm thick at center, 3–6 mm thick half-way between center and margin, pale yellow to light yellow (3A3–5), staining deeper chrome yellow (3A7) when bruised. Hymenophore poroid, sinuate-decurrent to decurrent; tubes 2–9 mm long, pale yellow to light yellow (3A3–5), deeper chrome yellow when bruised; pores 0.3–1.5 mm in diam, angular, irregular surface, pale yellow to light yellow (3A3–5), staining pale orange (between 4A6 and 5A6) with time when bruised. Stipe 47–75 mm long, 9–19 mm wide, central, solid, equal or slightly enlarged at base, usually curved, densely reticulate over the upper 2/3; surface dry, background color yellow (1A5) on upper part, lower part golden blonde (4B4), staining vivid yellow (2A8) at first and changed to light brown (6D8) later when injured; reticulum light yellow to yellow (3A4–6) entirely, or only above, and then brownish-grey below (between 4B3 and 5C3); context white to yellow, staining deeper chrome yellow when cut, at least when young. Spore print not obtained. Basal mycelium pale yellow to chrome yellow, with some fine rhizoids. Odor fungoid, weak. Taste bitter.

Macrochemical reactions: Pileipellis reddish with violet tinge around the spot in KOH solution, pale orange in NH4OH solution; pileus context pinkish white with KOH, yellow by reversal of the oxidation with an additional greenish tinge with NH4OH solution.

Micromorphology: [55/1/1] (8–)9–11(–11.5) × (3.6–)3.7–4.3(–4.4) µm, 10.3 × 4.0 µm on average, Q = (1.9–)2.4–2.9(–3), 2.59 on average, subfusiform to ellipsoid, greenish grey to greyish green (1C2–3) in water and KOH, smooth. Basidia (17–)18–25(–26) × 6–10 µm, 21.1 × 8.3 µm on average, clavate, four-spored, hyaline in KOH; sterigmata 2–4 μm long. Hymenophoral trama bilateral of the boletus-type, composed of hyphae 3–5 μm wide, hyaline in KOH. Cheilocystidia 34–46 × 7–13 µm, 40.7 × 9.9 µm on average, abundant, ventricose or subfusiform, usually with yellowish-brown (5E8) pigmented contents in water, but without cell wall encrustations. Pleurocystidia 24–40 × 7–11 µm, 32.1 × 9 µm on average, clavate or subfusiform, with yellowish-brown (5E8) pigmented contents in water, without cell wall encrustations. Pileipellis a trichoderm about 70–100 μm thick, composed of slightly interwoven hyphae 5–10 μm wide, brown (6E6) to blackish-brown in water and KOH; terminal cells 20–50 × 7–10 μm, narrowly clavate or subcylindrical. Pileal trama made of hyphae 6–10 μm, hyaline in KOH. Stipitipellis a disrupted hymeniderm about 60–90 μm thick, composed of emergent hyphae, hyaline in potassium, with 20–40 × 7–9 μm clavate or subfusiform terminal cells. Stipe trama composed of parallel hyphae, 5–8 μm wide, cylindrical, hyaline in KOH. Clamp connections not seen in any tissue.

Habitat: Solitary or in small groups on the leaves litter in forests dominated by Fagaceae (Quercus, Lithocarpus, Castanopsis) and/or Dipterocarpaceae (Shorea, Dipterocarpus).

Distribution: Currently only known from northern Thailand.

Materials examined: THAILAND. Lampang Province, Mueang Pan District, along Road 1252, 18°55’50’’N, 99°23’30’’E, elev. 1,420 m, Olivier Raspé & Komsit Wisitrassameewong, OR0570; Chiang Mai Province, Mae On District, Behind Tharnthong Lodges, 18°52’06’’N, 99°18’06’’E, elev. 760 m, 8 Aug 2013, O. Raspé & Benjarong Thongbai, OR0708 (MFLU13-0610).

Fig. 1 Maximum likelihood phylogenetic tree inferred from the three-gene dataset (atp6, rpb2, tef1), including Retiboletus brevibasidiatus, R. fuscus, R. nigrogriseus and selected Retiboletus species. Four species were used as outgroup taxa: Borofutus dhakanus, Ionosporus longipes, Rhodactina rostratispora, Spongiforma thailandica. Bootstrap frequencies ≥ 70% and posterior probabilities ≥ 0.95 are shown above supported branches. The prefix “GB” before voucher numbers indicates that sequences were retrieved from GenBank.

Fig. 2 Basidiomata of Retiboletus brevibasidiatus in the field. A: OR0570. B: OR0110 (holotype). Bars: 2 cm.