Retiboletus sinogriseus 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 sinogriseus Yan C. Li & T. Bau sp. nov. Figures 2d-f , 4

Etymology.

sino (Latin) = China, reflecting that the basidiomata were collected in China + griseus for similarity of the basidiomata of this species to Retiboletus griseus .

Type.

China. Liaoning Province: Anshan City, Qianshan, alt. 400 m, 25 Aug 2015, J. Li 260 (holotype: KUN-HKAS 91288!).

Description.

Basidiomata medium-sized. Pileus 6-7.2 cm in diameter, subhemispherical to applanate, sometimes convex; surface tomentose, grayish-brown (5D2-3) to brown (5E4), rimose when dry, always cracked into small squamules on grayish (4B1) to whitish (2A1) background; context 1-2 cm thick in the center of pileus, white (1A1), unchanging when injured. Hymenophore adnate, sometimes slightly depressed around apex of stipe; pores angular, 0.3-1 mm wide, tubes up to 14 mm long, yellow (4C3-4) to grayish-yellow (4B2-3), unchanging when injured. Stipe 6-8 × 1.1-1.5 cm, subcylindrical, solid; surface dry, pale yellow at apex, blackish-yellow towards the base, entirely covered with moderately developed reticulum; context white to cream in the upper part and yellowish to yellow downwards, unchanging when injured; basal mycelium yellow. Taste and odor indistinct.

Basidia 21-27 × 9-11 μm, clavate, thin-walled, four-spored; sterigmata 4-5 μm long. Basidiospores [40/2/2] (9) 10.0-13.5 (-14.0) × (3) 4.0-5.0 (-5.5) μm, Q = (2.25-) 2.5-3.25 (-3.42), Qm = 2.88 ± 0.32, subfusiform to ellipsoid, slightly thick-walled (up to 0.5 μm), hyaline to yellowish in KOH, olive-brown to yellowish-brown in Melzer’s reagent, smooth. Hymenophoral trama boletoid. Cheilo- and pleurocystidia 35-56 × 7-12 μm, abundant, subfusiform to fusiform, thin-walled, with yellowish-brown to brown contents, without encrustations. Pileipellis a subcutis, 100-120 μm thick, composed of thin-walled filamentous hyphae 4-7 μm wide, with subcylindrical to clavate terminal cells 33-72 × 4-6 μm, sometimes with subacute apex, colorless to pale yellowish-brown in KOH, yellow-brown to brownish in Melzer’s reagent. Pileal trama composed of thin-walled hyphae 4-9 μm wide, colorless to pale yellowish-brown in KOH, yellow-brown to brownish in Melzer’s reagent. Clamp connections absent in all tissues.

Habitat, ecology and distribution.

Solitary on the ground in mixed forests dominated by plants in the families Fagaceae and Pinaceae ; currently known from northeastern China.

Additional specimens examined.

China. Liaoning Province: Anshan City, Qianshan, alt. 400 m, 25 Aug 2015, J. Li 258 (KUN-HKAS 91286).

Discussion.

Retiboletus sinogriseus has a grayish-brown to brown pileus, a pale yellow to blackish-yellow stipe. Such traits are very similar to those of R. griseus . Interestingly, R. sinogriseus clusters with R. griseus with strong statistical support (Fig. 1 ). However, R. griseus , originally described from North America but not found in China yet, has a distinctly pallid hymenohore and broad pileipellis hyphae which are up to 17 μm wide ( Singer 1947; Smith and Thiers 1971; Ortiz-Santana et al. 2007). Additionally, the R. sinogriseus / R. griseus clade is clustered with R. zhangfeii N.K. Zeng & Zhu L. Yang, R. nigrogriseus and R. nigerrimus ( R. Heim) Manfr. Binder & Bresinsky (however without bootstrap support). In this assemblage, R. zhangfeii differs significantly from R. sinogriseus by its differently colored pileus, hymenophore, stipe and context ( Zeng et al. 2016). Retiboletus nigrogriseus has a black to gray pileus, white to grayish white hymenophore, white to olivaceous contex in the stipe and much smaller basidiospores 8-10.5 × 3.5-4.5 μm. Retiboletus nigerrimus , originally described from Papua New Guinea, has a pileus with a distinctive blue tinge, a context lemon yellow in pileus and orange in the base of stipe and longer and narrower basidiospores 11.5-14.5 × 3.6-4.6 μm ( Heim 1963).

Nine species of Retiboletus were recorded from China, including two new species described herein. For the convenience of identification, a key to the species in China is given below.

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 4. Microscopic features of R. sinogriseus (KUN-HKAS 912889). a Basidiospores b basidia and pleurocystidium c pleurocystidia d cheilocystidia e pileipellis. Scale bars: 10 μm.