Russula minor, Song & Xie & Buyck, 2021

Song, Yu, Xie, Xiu-Chao & Buyck, Bart, 2021, Two novel species of subgenus Russula crown clade (Russulales, Basidiomycota) from China, European Journal of Taxonomy 775, pp. 15-33 : 25-28

Russula minor Y.Song sp. nov.

MycoBank: MB837427

Index Fungorum: IF558489

Figs 5–6 , 7B

Diagnosis

Russula minor sp. nov. is mainly characterized by its very small basidiocarp with thin context and pink to rosy pileus less than 2.5 cm in diam., pileipellis very easy to peel off, white to cream lamellae with few lamellulae, often curved and hollow to multi-chambered stipe, spores with conical to cylindrical warts never connected, very small basidia and gelatinized pileipellis with slender terminal cells and abundant pileocystidia, and pleurocystidia weakly SV+ (slightly becoming brownish) or SV-, while pileocystidia becoming brown in SV.

Etymology

Referring to its very small basidiocarp.

Type material

Holotype CHINA • Guangdong Province, Zhaoqing City, Dinghushan Biosphere Reserve , on the ground in evergreen broad-leaf forest mainly with plants in Fagaceae ; 12 Sep. 2016; Y. Song, K18043001 ; GenBank nos.: MN275666 (ITS), MK881964 (nLSU), MK882091 (mtSSU), MT085496 (rpb1), MK880691 (rpb2), MT085599 (tef1); GDGM79686 .

Additional material examined

CHINA • Guangdong Province, Zhaoqing City, Dinghushan Biosphere Reserve, on the ground in evergreen broad-leaf forest; 8 Sep. 2018; F. Yuan and Y. Song, K18090802; GenBank no: MN275665 (ITS); GDGM79687 • same data as for preceding; F. Yuan and Y. Song, K18090827; GenBank no: MN275667 ; GDGM79688 • same data as for preceding; 10 Sep. 2018; F. Yuan and Y. Song, K18091022; GenBank no: MN275668 ; GDGM79689 .

Description

Basidiocarp very small (pileus diameter less than 3 cm). Pileus 0.8–2.5 cm in diam., hemispherical to convex when young, turning applanate with depressed center or infundibuliform at maturity; surface dry, viscid when wet, sometimes slightly villose at center, easy to peel to 2/3 radius, white (#FFFAFA) to pinkish (#FAEBD7) at margin, pink, fuchsia pink to rosy (#F97D8E, #C85868, #DF828F) at center; margin smooth and entire at first, turning striate with age, sometimes cracked. Lamellae adnate, dense at first, becoming scattered with age, interveined, white when young, turning yellowish cream (#FCF3CF, #FEF9E7) at maturity; edge concolorous, smooth; lamellulae irregularly dispersed. Stipe central, fleshy, fragile, cylindrical, often curved, solid at first, turning hollow to multi-chambered with age, 0.7–1.2 × 0.2–0.4 cm, white to yellowish cream (#FCF3CF, #F8F9C2), sometimes slightly villose. Context white, sometimes yellowing at lower part of the stipe; taste mild; odor indistinct. Spore print pale cream (#F3E2A9).

Basidiospores subglobose to ellipsoid, rarely globose, (40/2/2) (5.0–)5.3–5.8–6.1(–6.6) × (4.1–) 4.3–4.6–4.9(–5.2) μm, [Q = (1.11–)1.15–1.22–1.30], hyaline in 5% KOH; ornamentation amyloid, conical to cylindrical warts less than 1.5 μm in height, mostly isolated, rarely fused into short crest, but not reticulate; suprahilar spot amyloid. Basidia clavate, 2- or 4-spored, thin-walled, with irregular contents or dorplets, small, (17–)17.5–21–27(–29.5)×7–8.5–9.5(–10) μm; sterigmata 2.2–4.8 ×0.9–1.7 μm. Pleurocystidia subcylindrical to fusiform, with obtuse, papillate or mucronate apices, thin-walled, with irregular refractive contents, weakly SV+ or SV-, 26.5–36–48(–52.5)×4–6–7 μm. Cheilocystidia similar to pleurocystidia, but shorter, 20–31–40(–47) in length. Subhymenium pseudoparenchymatous. Lamellar trama composed of numerous sphaerocytes surrounded by connective hyphae, sphaerocytes measuring 21–28 μm in diam. Pileipellis 60–120 μm thick, gelatinized, composed of ascending to erect hyphae; hyphae cylindrical, thin-walled, hyaline, sometimes branched, 1.5–4 μm wide; terminal cells cylindrical, slender, with obtuse or tapering apices, thin-walled, hyaline, (7–)8–18–31(–44) × 2–2.5–3.5 μm. Pileocystidia one-celled, abundant, subcylindrical to subclavate, obtuse or papillate, sometimes branched, with refractive contents, becoming brown in SV, (15.5–)16–46–106(–130) × 3–4.5–6.5 μm. Stipitipellis a cutis, composed of cylindrical, septate, thin-walled, hyaline hyphae measuring 1-3 μm in diam.; terminal cells cylindrical with obtuse apices, hyaline, 9–13.5–16(–18) ×2.5–3–4 μm. Caulocystidia subcylindrical, with obtuse apices, with irregular refractive contents, becoming brown in SV, (16.5–)21–35–62(–85.5)× 3–5–6.5 μm. Clamp connections absent in all tissues.

Figures

Fig. 5. Russula minor Y.Song sp. nov. A, E–F. Holotype, GDGM79686. B. GDGM79689. C. GDGM79687. D. GDGM79688. A–E. Fruiting bodies. F. Basidiospores under scanning electron microscope. Scale bars: A–E = 1 cm; F = 1 µm.

Fig. 6. Russula minor Y.Song sp. nov., holotype (GDGM79686). A. Basidia. B. Pleurocystidia. C. Cheilocystidia. D. Caulocystidia. E. Terminal elements of pileipellis. F. Pileocystidia. Scale bars = 10 μm. Drawing by Yu Song.

Fig. 7. Line drawings of basidiospores. A. Russula coronaspora Y.Song sp. nov. (GDGM79711) B. R. minor Y.Song sp. nov., holotype (GDGM79686). Scale bars = 1 μm. Drawing by Yu Song.