Lactarius gibbosus X. H. Wang, Ran Wang & S. Q. Cao 2024, sp. nov.

Lactarius gibbosus X.H. Wang, Ran Wang & S.Q. Cao, sp. nov., Fig. 3 MycoBank number: MB 854361 Etymology:—referring to the swollen hyphae in the pileipellis. Holotype:— CHINA: Yunnan Prov., Menglian Co., Gongxin Town, Gongxin village, N22º16′46.13′′ E99º16′27.98′′, in broad-leaved forest with trees of Castanopsis and Lithocarpus, 05 Sept. 2021, coll. R. Wang, no. rml-887 (KUN-HKAS 135134! GenBank: ITS PP88746; gpd PP898319; nuc-LSU PQ273275; rpb1 PQ274843; rpb2 PQ274831; tef1 PQ274837). Diagnosis:—Different from all other species of L. sect. Deliciosi by the dry and waxy pileus and pileipellis with swollen thick-walled cells and lacking slimy layer. In addition, the azonate pileus and macrocystidia with thick golden brown contents can help to separate it from L. hatsudake. Basidiocarps medium-sized to big, stout. Pileus 69–100 mm in diam., center umbonate, margin applanate to slightly wavy, striate, shallowly infundibuliform when mature; surface dry, waxy, grayish pink often mixed with pale lilac tinge at the center, grayish purple towards the margin, azonate; context 3 mm thick, grayish purple, dull purple when bruised, with dark vinaceous red dots. Lamellae 4–5 mm broad, subdistant, short decurrent, grayish purple, dark purple when bruised, unchaning to green or bluish. Stipe 36–43 × 10–17 mm, central, equal or slightly tapering downwards, hollow; surface smooth, dry, paler than the lamellae. Latex scanty, dark vinaceous red, unchanging. Spore print unknown. Basidiospores (40/2/1) (5.5) 6.0– 6.5 –7.5 (8.0) × 5.0– 5.5 –6.0 (6.5) μm, broadly ellipsoid to ellipsoid [Q = (1.14) 1.16–1.24 (1.25), Q = 1.21 ± 0.06], ornamentation up to 1.0 μm high, composed of long ridges partially connected, not forming a reticulum, closed meshes and isolated warts rare; plage not amyloid. Basidia 40–52 × 8–10 μm, clavate, 4-spored. Pleuromacrocystidia abundant, 42–90 × 6–14 μm, base originating from subhymenium, fusiform, clavate, with a blunt apex, filled with thick golden-brown contents, contents thicker at the middle upper part. Hymenial pseudocystidia abundant, 2–4 μm broad, with golden-brown contents. Lamella edge sterile; cheilomacrocystidia common, 27–60 × 5–10 μm, clavate with a blunt apex, filled with golden-brown contents, rarely with sparse contents; marginal cells 22–32 × 6–8 μm, cylindrical, clavate. Pileipellis 50–130 μm thick, of irregularly swollen cells mixed with hyphoid cells, some terminal cells thick-walled with wall to 1 µm thick, swollen cells 10–15 μm broad, hyphoid cells 5–8 µm broad, strongly gelatinized, nearly colorless to pale yellowish brown. Lactiferous hyphae abundant, 3–8 μm broad, golden brown. Stipitipellis an (ixo)cutis, up to 50 μm thick; hyphae 2–6 μm broad, strongly gelatinized. Trama of pileus and stipe with abundant rosettes. Clamp connections absent. Note: This is a unique species in L. sect. Deliciosi. The dry and waxy pileus surface has never been found in the section. Under microscope, the pileipellis with swollen and even thick-walled cells is unexpected, even reminiscent of species of Lactifluus (Pers.) Roussel (1806: 66). This is totally different from the diagnostic ixocutis pileipellis of the section. The macrocystidia are filled with golden brown contents, very similar to pseudocystidia. These characters are sufficient to recognize it as a new species. The closest relative of this new species is L. subindigo, a blue-colored species also growing with fagaceous trees and found in southern China. This is the first time that red-colored species is found from fagaceous forest.