Retiboletus ater Yan C. Li & T. Bau, 2020

Liu, Hai-Ying, Li, Yan-Chun & Bau, Tolgor, 2020, New species of Retiboletus (Boletales, Boletaceae) from China based on morphological and molecular data, MycoKeys 67, pp. 33-44 : 33

Retiboletus ater Yan C. Li & T. Bau sp. nov. Figures 2a-c , 3

Etymology.

ater referring to the color of the basidiomata.

Type.

China. Yunnan Province: Jingdong County, Ailaoshan National Nature Reserve, alt. 2500 m, 14 July 2008, Y.C. Li 1215 (holotype: KUN-HKAS 56069!).

Description.

Basidiomata small to medium-sized. Pileus 3-5 cm in diameter, hemispherical to applanate, surface dry, densely subtomentose, black (4F3) to blackish (4E2) in the center and gray (3D1) or yellowish-gray (3C2-3) towards margin, context 2.5 cm thick in the center of the pileus, pallid gray (2D1) to cream (2C3-4), unchanging when bruised. Hymenophore adnate or slightly depressed around apex of stipe; pores angular, tubes up to 11 mm long, 0.3-1 mm wide, white (2B1) when young and yellowish (2A2) in age, becoming brownish-yellow (5C7-8) when injured. Stipe 4-6 × 0.8-1.2 cm, clavate to flexuous, solid; surface dry, blackish to gray, prominently and coarsely reticulate over the upper 1/3; context white (2A1) in the upper part and yellowish to cream yellow downwards, unchanging when injured; basal mycelium white (2A1). Taste and odor indistinct.

Basidia 26-38 × 6-10 μm, clavate, thin-walled, 4-spored, hyaline to yellowish in KOH. Basidiospores [60/3/2] (7)8-10.5(11) × 3-4.5(5) μm [Q = (1.89) 2-3.33 (3.67), Qm = 2.52 ± 0.42], subfusiform and inequilateral in side view with shallow suprahilar depression, elongate fusoid or narrowly oblong in ventral view, slightly thick-walled (up to 0.5 μm), brownish to yellowish-brown in KOH, olive-brown to brown in Melzer’s reagent, smooth. Hymenophoral trama boletoid; hyphae cylindrical, 3.5-9 μm wide, hyaline to yellowish in KOH, yellowish to brownish-yellow in Melzer’s reagent. Cheilo- and pleurocystidia 26-55 × 6-10 μm, abundant, subfusiform to fusiform, thin-walled, with yellowish-brown contents, surface without encrustations. Caulocystidia forming the reticulum over the stipe surface, similar to cheilo- and pleurocystidia. Pileipellis a trichoderm about 280 μm thick, composed of more or less vertically arranged, slightly interwoven, brown to dark brown hyphae, 5-15 μm wide; terminal cells 45-111 × 9-15 μm, narrowly clavate to subcylindrical or subfusiform, sometimes narrowly mucronate, rostrate, slightly thick-walled (up to 0.5 μm), hyaline to yellowish in KOH, yellowish to brownish-yellow in Melzer’s reagent. Pileal trama composed of thin- to slightly thick-walled (up to 0.5 μm) hyphae, 5-11 μm wide, hyaline to yellowish in KOH, yellowish to brownish-yellow in Melzer’s reagent. Clamp connections absent in all tissues.

Habitat, ecology and distribution.

Solitary on the ground in forests dominated by plants in the family Fagaceae ; currently known from southwestern China.

Additional specimens examined.

China. Yunnan Province: Jingdong County, Ailaoshan National Nature Reserve, alt. 2500 m, 14 July 2008, Y.C. Li 1224 (KUN-HKAS 56078).

Discussion.

Retiboletus ater is characterized by the black to blackish or gray to yellowish-gray pileus, the white to yellowish hymenophore, the gray to brownish-gray stipe, the prominent and coarse reticulum over the upper 1/3 of the stipe and the trichoderm pileipellis with hyphae 9-15 μm wide. It generally shares the same colored pileus and hymenophore with R. fuscus (Hongo) N.K. Zeng & Zhu L. Yang, R. griseus (Frost) Manfr. Binder & Bresinsky, R. nigrogriseus N.K. Zeng, S. Jiang & Zhi Q. Liang, and R. pseudogriseus N.K. Zeng & Zhu L. Yang. However, R. fuscus is characterized by an overall reticulate stipe, slight longer basidiospores (9-12 × 3.5-4.5 μm) and narrower pileipellis hyphae (4-8 μm wide) ( Zeng et al. 2016). Retiboletus griseus has a reticulum over the upper 2/3 of the stipe, a cream or grayish-brown stipe often with orange-yellow stains when hurt, and a distribution in North/Central America ( Smith and Thiers 1971; Ortiz-Santana et al. 2007). Retiboletus nigrogriseus is characterized by the white to olivaceous contex in the stipe, the entirely reticulate stipe and the cutis pileipellis with hyphae 4-10 μm wide. Retiboletus pseudogriseus has a grayish white pileus which is covered with brown to blackish brown squamules, white context becoming brown when injured, and a slender and completely reticulate stipe.

In the phylogenetic analysis (Fig. 1 ), R. ater forms an independent lineage within Retiboletus , future studies would require more molecular sequence data to help fully resolve its evolutionary relationships to the other species.

Figures

Figure 1. Maximum likelihood phylogenetic tree of Retiboletus inferred from the combined nuclear dataset (nrLSU + TEF 1 - α). Bootstrap frequencies (> 50 %) are shown above supported branches. Newly sequenced collections are boldfaced in black. Species vouchers are provided after the species name.

Figure 2. Habitat of the new Retiboletus species. a-c R. ater (from KUN-HKAS 56069) d-f R. sinogriseus (d from KUN-HKAS 91288 e-f from KUN-HKAS 91286).

Figure 3. Microscopic features of R. ater (KUN-HKAS 56069). a Basidiospores b basidia and pleurocystidium c cheilo- and pleurocystidia d pileipellis. Scale bars: 10 μm.