Aureoboletus microcarpus N.K. Zeng, Xu Zhang & S. Jiang, 2022

Zhang, Xu, Tian, Run, Tang, Li-Ping, Liang, Zhi-Qun, Zhang, Wen-Hao, Jiang, Shuai, Wang, Cheng-Kai & Zeng, Nian-Kai, 2022, Morphological and phylogenetic evidence reveal three new species of Aureoboletus (Boletaceae, Boletales) from China, Phytotaxa 567 (2), pp. 127-148 : 140-141

Aureoboletus microcarpus N.K. Zeng, Xu Zhang & S. Jiang , sp. nov. ( Figs. 3C – D , 5 )

MycoBank: MB841621

Etymology:—Latin “ microcarpus ” refers to the small basidiomata of the new species.

Diagnosis:—Differs from other species of Aureoboletus by a very small and glutinous basidioma, a dull reddishbrown, violet brown pileal surface, a pileal margin usually with white to subhyaline veil remnants when young, cylindrical basidiospores, and an ixotrichoderm-type pileipellis.

Holotype:— CHINA. Hainan Province: Yinggeling of Hainan Tropical Rainforest National Park, elev. 550 m, 7 July 2020, N. K. Zeng 4468 ( FHMU4688 ). GenBank accession number: 28 S = OK327017 , ITS = OM 200341 , RPB2 = OM 280449 .

Description:— Basidiomata very small-sized. Pileus 0.4–1.9 cm in diam., subhemispherical when young, then broadly convex to plane; margin usually with white (1A1) to subhyaline veil remnants when young; surface viscid, distinctly wrinkled, brown (6D3) to blackish brown (6E3); context 0.1–0.2 cm thick in the center of the pileus, white (1A1), unchanging in color when cut. Hymenophore poroid, adnate or slightly decurrent; pores approximately 0.5 mm in diam., subround, yellowish (1A3), unchanging in color when cut; tubes 0.1–0.3 cm long, pale yellow (1A6), unchanging in color when cut. Stipe 1.5–2.2 × 0.1–0.3 cm, central, subcylindrical, solid; surface yellowish-white (1A3), usually covered with a mucilaginous layer; context white (1A1), unchanging in color when cut. Basal mycelium white (1A1). Odor indistinct.

Basidia 22–30 × 7–10.5 μm, clavate, thin-walled, 4-spored, hyaline or yellowish in KOH; sterigmata 3–4 μm long. Basidiospores [150/3/3] 8.5–12.5(–13) × 4–5.5 μm, Q = (1.87–)2–2.77(–3), Qm = 2.4 ± 0.26, cylindrical, smooth, moderately thick-walled (up to 1 μm), yellowish brown (3B8) in KOH. Cheilocystidia 24–36 × 8–13 μm, fusoidventricose, moderately thick-walled (up to 1 μm), yellowish-white (1A3) or hyaline in KOH. Pleurocystidia 25–44 × 10–14 μm, subfusiform or fusiform, thin-walled, yellowish-brown (3B8) in KOH. Hymenophoral trama bilateral, composed of hyphae 3–8 μm wide, moderately thick-walled (up to 1 μm), yellowish (1A2) in KOH. Pileipellis an ixotrichoderm 200–300 μm thick, embedded in a gelatinized matrix, made up of hyphae 4–8 μm wide, moderately thick-walled (up to 1 μm), yellowish-white (1A3) or hyaline in KOH; terminal cells 26–39 × 4.5–8 μm, narrowly clavate or subcylindrical, with obtuse apex. Pileal trama composed of hyphae 3–8 μm wide, moderately thick-walled (up to 1 μm), hyaline in KOH. Stipitipellis a hymeniderm 300–500 μm thick, embedded in a gelatinized matrix, made up of hyphae 4–5 μm wide, moderately thick-walled (up to 1 μm), yellowish-white (1A3) or hyaline in KOH; terminal cells 25–43 × 4–5 μm, subclavate, subcylindrical, or subfusiform, with obtuse apex. Stipe trama made up of parallel hyphae 4–10 μm wide, thin- to slightly thick-walled (up to 0.5 μm), hyaline in KOH. Clamp connections not observed in any tissue.

Habitat:—Solitary on the ground in forests dominated by fagaceous trees ( Lithocarpus spp. ).

Known distribution:—Southern China (Hainan Province).

Additional specimen examined:— CHINA. Hainan Province: Yinggeling of Hainan Tropical Rainforest National Park, elev. 550 m, 3 July 2020, N.K. Zeng4465 (FHMU4722); same location and date, N.K. Zeng4467 (FHMU4695).

Notes: Phylogenetically and morphologically, A. microcarpus is closely related to A. glutinosus Ming Zhang & T.H. Li (2019: 121) , A. marroninus T.H. Li & Ming Zhang , and A. tenuis T.H. Li & Ming Zhang (2015: 182) ( Fig. 2 ). However, A. glutinosus , originally described from Hunan Province, central China, has a reddish-brown to ruby pileal surface usually with irregular reticulations and darker folds, and longer basidiospores [(9.5–)10–13.5 × (4–)4.5–5 μm] ( Zhang et al. 2019); A. marroninus , firstly described from Guangdong Province, southern China, has a darker (violet brown or maroon) pileal surface, a context often slightly changing to blue, especially in the lower portion of the stipe when exposed, and smaller basidiospores [(8–)8.5–10 × 4–4.5(–5) μm] (Zhang et al. 2015); A. tenui s, originally described from Guangxi Province, southern China, has a larger pileus (2–3.5 cm in diam.), a wrinkled to shallowly reticulate pileal surface, an absence of appendiculate veil remnants, and a greyish-red to brownish-orange stipe ( Zhang et al. 2014). Moreover, the phylogenetic distance is 0.167 between our new species A. microcarpus and its sister taxon A. glutinosus ( Fig. 2 ), which falls within the range of values of 0.012 to 0.42 for the inter-specific variation of Aureoboletus species.

Figures

FIGURE 2. Phylogram inferred from a three-locus (28S, TEF1 and RPB2) dataset using RAxML. BS ≥ 70% and PP ≥ 0.95 are indicated above or below the branches as RAxML BS/PP. SW, southwest; SE, southeast; NE, northeast.

FIGURE 3. Basidiomata of Aureoboletus species. A–B A. guangdongensis (FHMU3797, holotype); C–D A. microcarpus (C from FHMU4722; D from FHMU4695); E–I A. rugosus (E from FHMU6509, holotype; F from FHMU2766; G–I from FHMU6510). Bars = 1 cm. A–D photos by N.K. Zeng; E photo by W.H. Zhang; F photo by G.L. Zhang; G–I photos by L.P. Tang.

FIGURE 5. Microscopic features of Aureoboletus microcarpus (FHMU4688, holotype). A. Basidiospores. B. Basidia. C. Cheilocystidia. D. Pleurocystidia. E. Pileipellis. Bars = 10 μm. Drawings by X. Zhang.