Corneroboletus indecorus

Corneroboletus indecorus (Massee) N.K. Zeng & Zhu L. Yang, in Zeng et al., Mycologia 104(6): 1423 (2012)

Basidiomata small to medium (Figure. 3A–D). Pileus 3–6 cm diam, hemispherical when young, then convex or plane, finally slightly depressed in the center; surface dark red to reddish brown (yellowish brown to dark brown when dried) but paler toward the pileal margin, mucilaginous, rugose, densely covered with whitish to dirty white, small conical to subconical to irregularly shaped squamules (universal veil remnants); margin incurved, usually appendiculate with whitish veil remnants; context 0.3–0.6 cm thick in the center of the pileus, cream to yellowish, unchanging in color when injured. Hymenophore poroid, depressed around apex of stipe; pores angular, 0.3–0.5 mm diam, yellowish when young, then yellow to olivaceous yellow, turning brownish to reddish brown slowly when injured; tubes 0.7–1 cm long, yellowish. Stipe central, 4–8 × 0.5–0.7 cm, subcylindrical, slightly attenuate downward, solid, flexuous; stipe surface concolor with pileal surface, densely covered with white, small conical to subconical to irregularly shaped squamules (universal veil remnants), but apical part bright yellow, nearly smooth but surrounded by a slightly thickened smeary zone just below about 1 cm of the stipe-apex; context russet but bright yellow at the apical part, unchanging in color when injured. Basal mycelium whitish. Odor distinct. Flavor slightly sweet.

Basidia 21–41 × 8–14 μm, clavate, thin-walled, four-spored, colorless to yellowish in KOH; sterigmata 4–6 μm long (FIGS. 5A, 6A, 7A, 8A). Basidiospores [360/18/5](8.5)9–13(14) × (4.5)5–6(6.5) μm, Q = (1.55)1.80–2.33(2.60), Qm = 2.01 ± 0.17, subfusiform to ellipsoid, slightly thick-walled (< 1 μm thick), yellowish to yellowish brown in KOH, smooth under the light microscope but irregularly warty to irregularly bacillate under SEM (Figures. 4, 5B, 6B, 7B, 8B). Tubetrama bilateral, comprising hyphae 3–12 μm wide, hardly to only slightly gelatinized, thin- to slightly thick-walled (up to 1 μm), colorless to yellowish in KOH. Cheilocystidia 30–46 × 5–8 μm, fusiform or subfusiform, thin-walled, colorless in KOH (Figures. 5C, 6C, 7C, 8C). Pleurocystidia 50–70 × 6–11 μm, similar to cheilocystidia in shape but larger in size (Figures. 5C, 6C, 7C, 8C). Pileipellis an ixohyphoepithelium 60–100 μm thick, dominantly composed of 2–4 layers of thin- to slightly thick-walled (up to 1 μm) ellipsoid to subglobose inflated cells, 10–52 × 8–24(32) μm, in H2O with reddish brown and in KOH yellowish to yellowish brown vacuolar pigment; terminal cells 10–47 × 6–18 μm, thin- to slightly thick-walled (up to 1 μm thick), subcylindrical, ellipsoid, subglobose to globose (FiguresS. 5D, 6D, 7D, 8D). Squamules on pileus a conical to subconical structure 150–250 μm thick, composed of ± vertically arranged, sometimes slightly interwoven, 3–8 μm wide, thin-walled, yellowish to brownish in KOH, filamentous hyphae connected with inflated cells or uninflated hyphal segments in the pileipellis (Figures. 5D, 6D, 7D, 8d). Pileal trama comprising hyphae 3–14 μm wide, thin- to slightly thick-walled (up to 1 μm), colorless to yellowish in KOH. Stipitipellis at the apex of the stipe a trichoderm-like structure of 50–70(130) μm thick, composed of thin-walled hyphae with subcylindrical, clavate or subfusiform terminal cells, 19–40 (74) × 5–11 μm, and commonly mixed with clavate, four-spored basidia (27–44 × 9–12 μm) (Figure. 5e); at the middle part of the stipe a trichoderm 40–80 μm thick, composed of thin-walled hyphae with subcylindrical, clavate or subfusiform terminal cells (15–55 × 6–13 μm), sometimes mixed with clavate, four-spored basidia (25–50 × 7–12 μm) (Figures. 5F, 6E, 7E, 8E). Squamules on stipe surface a conical to subconical structure, 240–500 μm thick, composed of 3–8 μm wide, thin-walled, yellowish to brownish in KOH, filamentous hyphae connected with slightly inflated cells or uninflated hyphal segments in the stipitipellis (Figures. 5F, 6E, 7E, 8E). Stipe trama composed of 3–17 μm wide, cylindrical, thin- to slightly thick-walled (up to 1 μm), colorless to yellowish in KOH, parallel hyphae. Clamp connections absent in all tissues.

Habit and habitat: Usually caespitose (Figure. 3C) on the ground in broadleaf forests dominated by Fagaceae.

Known distribution: Singapore (Massee 1909, 1914; Patouillard and Baker 1918, Corner 1972, Horak 2011), Malaysia (Watling 2001) and tropical China.

Index Fungorum number: IF561840

Figure 1. Phylogenetic placement of Corneroboletus indecorus within the Boletaceae inferred from a nrLSU dataset using RAxML. Bootstrap values ≥ 50% are shown.

Figure 2. Phylogenetic relationships of Corneroboletus indecorus within the Boletaceae inferred from a combined nrLSU + 5.8S rRNA + rpb2 dataset. Bootstrap values ≥ 50% are shown.

Figure. 3. Basidiomata of Corneroboletus indecorus (A, C, D from HKAS 63126; B from HKAS 63127). Scale bars = 2 cm.