Retiboletus Manfr. Binder & Bresinsky, Feddes Repert

Li, Jin, Wang, Zhen, Liu, En-De, Yang, Zhu L. & Li, Yan-Chun, 2022, Morphological and molecular data reveal Retiboletus cyanescens sp. nov. and the new subgenus Nigroretiboletorum (Boletaceae), Phytotaxa 572 (3), pp. 232-242 : 236

Retiboletus Manfr. Binder & Bresinsky, Feddes Repert 113(1–2): 36 (2002).

Type: Retiboletus ornatipes (Peck) Binder & Bresinsky, Feddes Repert 113(1–2): 37 (2002).

Description: Basidiomata small to medium-sized. Pileus subhemispherical to broadly convex, sometimes applanate; surface dry, velutinous, tomentose to matted tomentose, brown, yellow-brown, yellowish brown, grayish brown, gray, blackish gray, or black, sometimes with an olive, grayish green or blackish green tinge; margin always incurved; context yellow, pale yellow to light yellow, or white to grayish white or pallid gray to cream, unchanging or staining yellow, yellowish brown, pale brown, brown, blackish brown, or ferrugineous when injured. Hymenophore poroid, adnate or slightly depressed around apex of stipe; pores angular, grayish white, pale yellow, yellow to light yellow, unchanging or usually staining yellowish brown, brown to dark brown or pale orange when injured; tubes grayish white or yellowish to light yellow, unchanging or usually staining yellowish brown, pale brown, brown to dark brown when injured. Stipe central, subcylindric, solid, usually flexuous; surface dry, yellowish, yellow to brownish yellow or grayish white, gray, blackish yellow to blackish, always with yellow tinge downwards; surface always covered with concolorous or much darker reticulum; context yellow to bright yellow, or white to cream or grayish on the upper part, but with distinct yellow tinge downwards, unchanging or staining vivid yellow to yellowish brown or pale brown, brown to blackish brown or indistinct blue when injured; annulus absent. Basal mycelium white or yellow. Odor indistinct. Basidiospores smooth, subfusiform to ellipsoid. Cheilo- and pleurocystidia abundant, fusiform or subfusiform to fusoid-ventricose. Pileipellis subrepent to trichodermium composed of vertically arranged or interwoven thin-walled hyphae. Clamp connections absent in all tissues.

Ecology and distribution: Known from northern Central America and East Asia, associated with species of the families Fagaceae and Pinaceae .

Notes: The genus Retiboletus can be easily distinguish from other genera in Boletaceae by the grayish black or yellow tinged pileus, the concolorous stipes covered with reticulum or sometimes granular-like squamules, the yellow to bright yellow or white to grayish or cream hymenophore, and white or yellow basal mycelium. Species of the genus Boletus share the reticulate stipe with Retiboletus , but the surface of the immature poroid hymenophore of Boletus is covered with a layer of tangled white hyphae ( Cui et al. 2016). The genus Retiboletus receives high bootstrap support values as a monophyly in present and former studies. Species of this genus cluster into two major clades corresponding to two subgenera, i.e., R. subg. Nigroretiboletorum and R. subg. Retiboletus