Russula lacteocarpa Y.Song, 2023

Xie, Xiu-Chao, Buyck, Bart & Song, Yu, 2023, Species of Russula subgenera Archaeae, Compactae and Brevipedum (Russulaceae, Basidiomycota) from Dinghushan Biosphere Reserve, European Journal of Taxonomy 864, pp. 28-63 : 42-45

Russula lacteocarpa Y.Song sp. nov.

MycoBank: MB837415

Figs 5–6

Diagnosis

Russula lacteocarpa sp. nov. is mainly characterized by its milky to ivory white, dull pileus with striate margin, milky to ivory white gills, white stipe often irregularly fissured, very small spores with predominantly isolated, obtuse warts, slender cylindrical basidia and hymenial cystidia, and the onelayer pileipellis composed of gelatinized, incrusted hyphal terminations intermixed with often mucronate to rostrate pileocystidia.

Etymology

Named after its ivory-white pileus.

Type material

Holotype CHINA • Guangdong Province, Zhaoqing City, Dinghushan Biosphere Reserve , on the ground in evergreen broad-leaf forest mainly with Fagaceae trees; 24 Sep. 2017; Y. Song K17092401 ; GenBank

nos: MN 275537 (ITS), MK 881963 (nLSU), MK 882090 (mtSSU), MT 085528 (rpb1), MK 880690 (rpb2), MT 085598 (tef1); GDGM 79555.

Additional material examined

CHINA • Guangdong Province, Zhaoqing City, Dinghushan Biosphere Reserve , on the ground in evergreen broad-leaf forest mainly with Fagaceae trees; 16 Sep. 2016; Y. Song K16091606 ; GenBank no: MN275538 (ITS); GDGM79556 .

Description

Basidiomata small to medium sized. Pileus 4–8 cm in diam., hemispherical to convex when young, applanate with maturity; surface glabrous, dry, milky to ivory white (#FDFEFE, #FFFFF0), often slightly stained with reddish brown (#F4C270, #F3BD5D); margin entire when young, turning undulate with age, often cracked, not striate. Lamellae adnate, widely spaced, unequal with mostly one lamellula per lamella, usually very short but of unequal length, slightly narrowed and not anastomosing near stipe, strongly attenuated toward pileus margin, milky white to cream (#FDFEFE, #FFFFF0); edge entire, concolorous. Stipe central, 3–5 cm long, cylindrical, white (#FFFFFF, #FFFFF0), often stained with rust brown (#A0522D, #8B4513) at base, irregularly fissured, solid at first, turning spongy to hollow with age. Context white, becoming pink to light brown (#FFDEAD, #FFEBCD) when reacting with 5% FeSO 4. Taste mild. Odor indistinct. Spore print white (#FBFCFC).

Basidiospores subglobose to ellipsoid, rarely globose, small, (40/2/2) (4.1–)4.8–5.2–5.6(–5.9) × (4.1–) 4.6–5.0–5.4(–5.7) µm, [Q = (1.08–)1.12–1.26–1.38(–1.52)], hyaline in 5% KOH; ornamentation amyloid, composed of obtuse, isolated warts, up to 1 µm high, rarely fused into short crest; suprahilar spot inamyloid. Basidia (33.5–)36–44–50 × (5.0–)6.5–7.0–8.5 µm, subcylindrical to cylindrical, slender, thinwalled, 2- or 4-spored; sterigmata 4.3–5.3 × 1.2–2.1 µm. Pleurocystidia (43–)46–56–69(–72) × 3.5–5– 6 µm, cylindrical, with obtuse apices, thin-walled, one-celled, with irregular refractive contents, weakly positive in SV to negative in SV. Cheilocystidia 45–50–57.5 × 3.5–4.5–6 µm, similar to pleurocystidia, but smaller, negative in SV. Marginal cells not differentiated. Subhymenium pseudoparenchymatous. Lamellar trama composed of numerous sphaerocytes surrounded by connective hyphae. Pileipellis an ixo-cutis, 150–240 µm thick, composed of cylindrical, septate and hyaline hyphal terminations 1.5– 5.0 µm wide; terminal cells (7–)11–23–35 × 1.5–2–3.0 µm, slender, cylindrical, with obtuse apices, often incrusted. Pileocystidia (16.5–)20–42.5–60(–96) × 2–3–5 µm, cylindrical, mucronate to rostrate or constricted at upper part, thin-walled, with few refractive contents, unchanging in SV. Stipitipellis 50–80 µm, composed of uprising to erect hyphae measuring 1–3 µm wide, septate, thin-walled, hyaline; terminal cells cylindrical, with obtuse hyaline apices. Caulocystidia (15.5–)20–37–52(–60) × 1.5–3– 5.5 µm, cylindrical, apices obtuse or tapering, with refractive contents. Clamp connections absent in all tissues.

Comments

Russula lacteocarpa sp. nov. has a unique morphology in subgenus Archaeae. Its uniqueness is also reflected in its systematic position as both our ITS phylogeny ( Fig. 1 ) and the combined 5-locus analysis ( Fig. 2 ) place it in a basal position and sister to the rest of the subgenus with high support (BS = 85% and 100%, respectively). In the field, it is more reminiscent of species in subg. Brevipedum sect. Pallidosporinae or even some white capped Lactifluus . It is easily distinguished from these in the typically very small spores and the hymenophore that is not polydymous, but having a more or less equivalent number of lamellae and lamellulae. Together with R. cylindrica sp. nov. described above, it is also unique in the subgenus because of the very pale, creamy-whitish pileus.

Order Russulales Kreisel ex P.M.Kirk, P.F.Cannon & J.C.David Family Russulaceae Lotsy Genus Russula Pers. Subgenus Compactae (Fr.) Bon emend. Buyck & V.Hofst.

Figures

Fig. 5. Russula lacteocarpa Y.Song sp. nov., holotype (GDGM79555). A–B. Fruiting bodies. C. Basidia and pleurocystidia in hymenium. D–E. Basidiospores under scanning electron microscope. Scale bars: A–B = 1 cm; C = 10 µm; D–E = 1 µm.

Fig. 6. Russula lacteocarpa Y.Song sp. nov., holotype (GDGM79555). A. Basidia. B. Pleurocystidia. C. Cheilocystidia. D. Terminal cells and incrustations. E. Caulocystidia. F. Pileocystidia. Scale bars = 10 µm.

Fig. 1. Maximum Likelihood tree of Russula Pers. based on ITS sequences, bootstrap values higher than 50% were shown around the nodes. Sequences generated in this study are shown in bold blue.

Fig. 2. Maximum Likelihood tree of Russula Pers. based on concatenated 5-locus (LSU, mtSSU, rpb1, rpb2 and tef1) sequences. Bootstrap values higher than 50% were shown around the nodes. Sequences generated in this study are shown in bold blue.