Russula reticulofolia 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 : 45-49

Russula reticulofolia Y.Song sp. nov.

MycoBank: MB837416

Figs 7–8

Diagnosis

Russula reticulofolia sp. nov. is mainly characterized by its grey to black brown pileus with a surface that becomes minutely cracked toward the margin, abundantly and irregularly forked lamellae that sometimes even form a partial reticulate pattern, the remarkably small and reticulate spores, brown pigmented hyphae in pileipellis and stipitipellis, and pileocystidia with typical two-knobbed apices.

Etymology

Named after its frequently forked and reticulum-like lamellae.

Type material

Holotype

CHINA • Guangdong Province, Zhaoqing City, Dinghushan Biosphere Reserve , on the ground in coniferous and broad-leaf mixed forest; 13 Sep. 2016; Y. Song H16091306; GenBank nos: MN275541 (ITS), MK881932 (nLSU), MK882060 (mtSSU), MT085503 (rpb1), MK880659 (rpb2), MT085573 (tef1); GDGM79559 .

Additional material examined

CHINA • Guangdong Province, Zhaoqing City, Dinghushan Biosphere Reserve , on the ground in coniferous and broad-leaf mixed forest; 12 Sep. 2016; Y. Song H16091234; GenBank no: MN275542 (ITS); GDGM79560 .

Description

Basidiomata medium sized to large. Pileus 5–11 cm in diam., hemispherical to convex when young, turning applanate with depressed center to infundibuliform; surface dry, with villose squama, not easy to peel, off-white to grey (#F5F5DC, #DCDCDC) with dark brown (#6D614C, #988970) center, turning black brown (#403524, #5B5539) with age; margin entire, involute. Lamellae adnate to subdecurrent, narrow, unequal from irregularly dispersed lamellulae that often fuse with lamellae near the pileus margin, crowded, frequently and irregularly forked, especially near stipe but also near pileus margin, often partially reticulate, off-white to cream (#FFF5EE, #FFFAF0), sometimes tinged reddish brown (#D2B48C, #F5DEB3); edge entire, concolorous. Stipe central, cylindrical, solid at first, turning spongy with age, 5–8 cm long, off-white (#FFFFFF, #F8F8FF), with brown (#F5DEB3, #FAE5B4) powdery or villose pubescence on the surface. Context white. Odor pungent. Spore print white to cream (#FCF3CF).

Basidiospores subglobose to ellipsoid, rarely globose, small, (80/4/2) (5.4–)5.8–6.5–8.3(–8.7) × (5.1–) 5.4–5.9–7.5(–7.9) µm,[Q= (1.03–)1.04–1.15–1.27(–1.40)],hyaline in 5% KOH; ornamentation amyloid, composed of low ridges forming a complete or nearly complete reticulum; suprahilar spot inamyloid. Basidia 24.5–28–31(–33) × 5–7–8 µm, subcylindrical to clavate, thin-walled, 2-, 3- or 4-spored; sterigmata 1.8–4 × 1.1–1.6 µm. Pleurocystidia (35.5–)46–56.5–67(–69) × 3.5–5–6(–8) µm, projecting up to 25 µm, cylindrical, with mucronate to lanceolate or moniliform apices, non-septate, thin-walled, with few granular refractive contents, unchanging in SV. Cheilocystidia similar to pleurocystidia, 46– 53–57.5 × 3.5–5–6 µm. Subhymenium pseudoparenchymatous. Lamellar trama composed of numerous sphaerocytes surrounded by connective hyphae. Pileipellis 130–180 µm thick, orthochromatic in cresyl blue, divided into two layers: suprapeillis composed of ascending to erect hyphae, while subpellis a cutis, 120–150 µm thick; hyphae cylindrical, thin-walled, septate, often with brown pigment, 2–5 µm wide; terminal cells 13–32–43(–47) × 2.5–4–7.5 µm, subcylindrical to ampuliform, often tapering upwards, frequently with brown pigment. Pileocystidia (19.5–)21–26.5–37(–39) × 3.5–5.5–7 µm, not frequent, subcylindrical to fusoid, apices mucronate, frequently with two lateral knobs (referred to as the ‘Mickey Mouse’ type in Buyck et al. 2018), thin-walled, with refractive contents, unchanging in SV. Stipitipellis a cutis, composed of hyphae measuring 1–4 µm wide, cylindrical, septate, often with brown pigment; terminal cells (10–)12–20–27 × 2–3.5–6 µm cylindrical to lageniform, with obtuse apices, mostly slender, thin-walled. Caulocystidia 4.5–10.5 µm wide, not frequent, fusoid, mucronate to papillate, thin-walled, with few refractive contents. Clamp connections absent in all tissues.

Comments

Russula reticulofolia sp. nov. is similar to R. densifolia Secr. ex Gillet in its blackish brown pileus, very dense lamellae, reticulate spore ornamentations, but it differs from the latter species in its frequently and irregularly forked lamellae, sometimes even forming a partial reticulate pattern, and in the more slender hyphal extremities in the pileipellis. In addition, spores (7–11.2 × 6–8.6 µm) and basidia (39–67 × 7.2–12 µm) of R. densifolia ( Shaffer 1962) are obviously larger than in R. reticulofolia sp. nov., so are those of other species in this same complex. The similarities in ITS sequences between R. reticulofolia sp. nov. and its phylogenetically closest match ( R. densifolia subgroup A-4 from Japan) are about 97.5%, and these two species showed obvious genetic distance in the five-locus phylogenetic analysis. The combination of the unique morphological features and genetic distance support R. reticulofolia sp. nov. as a novel species.

Russula fuliginosa Sarnari also has blackish pileus, but it has fusiform hymenial cystidia, much bigger spores (7.2–8.8 × 5.6–7 µm) and basidia (39–52 × 8–11 µm) than R. reticulofolia sp. nov. ( Sarnari 1993).

Order Russulales Kreisel ex P.M.Kirk, P.F.Cannon & J.C.David Family Russulaceae Lotsy Genus Russula Pers. Subgenus Brevipedum Buyck & V.Hofst.

Figures

Fig. 7. Russula reticulofolia Y.Song sp. nov., holotype (GDGM79559) (A–B, E–F), GDGM79560 (C– D). A–D. Fruiting bodies. E–F. Basidiospores under scanning electron microscope. Scale bars: A–D = 1 cm; E–F = 2 µm.

Fig. 8. Russula reticulofolia Y.Song sp. nov., holotype (GDGM79559). A. Basidia. B. Pleurocystidia. C. Cheilocystidia. D. Caulocystidia. E. Pileocystidia. F. Terminal elements in pileipellis. Scale bars = 10 µm.