Russula pseudovirescens N. Roy, A.K. Dutta & Tanti, in Cao et al., Fungal Diversity 132: 615 (2025)
Index Fungorum number: IF 851248; MycoBank number: MB 851248; Facesoffungi number: FoF 15275; Figs. 1, 2, 3
Etymology – “pseudovirescens” refers to the morphological similarity to R. virescens.
Holotype – GUBH 20322.
Pileus small to medium-sized, 42–65 mm diam., convex with a slight central depression when young, becoming applanate to plano-convex with a depression towards the center to broadly convex with age; surface velvety, cracking to greenish patches, greenish green (27B5) to dull green (28D4) at the margin and viridine green (29A5) at the center when young to pastel green (27A4) at the margin to viridine green (29A5) towards the center when matured, unchanging on bruising and no reaction with KOH, very slowly turning red with guaiacol and unchanging with sulfovanillin, FeSO4 and phenol; margin incurved, acute, translucent striate, not cracking on maturity; context ca.7 mm thick at the center, up to 3 mm thick at margin, white (1A1), unchanging with KOH, light red with guaiacol, unchanging with phenol, sul fovanillin and FeSO4. Lamellae 3–5 mm broad, free, fragile, regular, distant with occasionally one series of lamellulae, white (6A1) to greenish white (28A2), discolors, pinkish red with sulfovanillin, orangish red with guaiacol, unchanging with KOH, phenol and FeSO4. Stipe 35 42 × 18–25 mm, central, cylindrical with slightly tapered at base, straight to sometimes slightly curved, surface smooth, white (1A1), no changing on bruising and unchanging with KOH, slowly turning orange-red to brick red with guaiacol, unchanging with sulfovanillin, phenol and FeSO4; context stuffed, white, turning pale yellowish with KOH, light orangish red with guaiacol, unchanging with sulfovanillin, phenol and FeSO4. Spore-print white. Odor sweet. Taste mild.
Spores (4.5–)5.0–6.4–6.5(–8.0) × (4.0–)4.5–6.0–6.5(–7.6) µm, globose to subglobose, hyaline, apiculus prominent, measuring 1.3 µm long, Q = 1.0–1.0–1.15; ornamentation small to medium sized, dense [(8–)10–12(–18) in a 3 µm diam. circle], composed of small amyloid conical warts, measuring 0.28–0.48 µm high, apex blunt, sometimes isolated, mostly fused (2–4 fusions in a circle), line connections (0–2 in a circle); suprahilar spot inamyloid. Basidia 36–48 × 7.5–10 µm, clavate, with oil droplets when viewed in KOH, thin-walled, 4-spored; sterigmata 1–1.5 µm long. Basidioles 28–38.5 × 6–10.0 µm, clavate, hyaline, thin-walled. Subhymenium pseudoparenchymatous. Lamellar trama mainly composed of spherocytes, measuring 36–43 × 9–15 µm. Hymenial cystidia dispersed, ca. 39.5–60 × 8.5–10 µm on gill sides, clavate to subclavate, thin-walled, apex obtuse or round to occasionally mucronate, mostly with heteromorphous contents towards the apex, not reacting with sulfovanillin, near gill edge ca. 33–52.5 × 5.5–9 µm, clavate to sphaeropedunculate, thin walled, apically obtuse or round to occasionally mucronate, with heteromorphous contents towards to the apical part of the cystidium, no reaction with sulfovanillin. Lamellae edge consists of occasional basidia; marginal cells undifferentiated. Pileipellis a trichoderm, orthochromatic in Cresyl blue, sharply delimited from the underlying spherocytes of the context, up to 330–425 µm deep, disrupted towards the pileus margin, distinctly two-layered, divided in a 25.5–46 µm deep suprapellis, composed of irregularly arranged, dense; subpellis comparatively less dense, consisting of irregularly arranged, hyaline hyphae measuring 5–10 µm broad. Acid-resistant incrustations absent. Pileocystidia arising from the hyphal terminations, towards the pileus margin measuring 30.5–47.5 × 2–5.5 µm, thin-walled, sub-cylindrical to fusiform, apically obtuse or acute, sometimes round or mucronate, contents heteromorphous, not reacting with sulfovanillin, terminal cells towards the margin measuring 28–45 × 1.8–5 µm, thin-walled, sub-cylindrical, with a round apex; Pileocystidia towards the pileus center scarce, similar in shape, measuring 30–46 × 2.2–5 µm, thin-walled, subcylindrical to fusiform, apically obtuse or acute, sometimes round or mucronate, contents heteromorphous, not reacting with sulfovanillin, terminal cells towards the center similar in size and shape, measuring 30–40 × 2–4.5 µm, thin walled, sub-cylindrical, with a round apex. Stipitipellis up to 146–160 µm thick, hyphae 1–2 µm broad, Caulocystidia 25.6–38.5 × 2.5–6.4 µm, thin-walled, ventricose to cylindrical in shape with a blunt apex. Stipe trama composed of subglobose spherocytes, measuring 15–38 × 9–19.0 µm. Clamp connections absent in all tissues.
Habit and habitat – Solitary, scattered, under Pinus kesiya.
Material examined – INDIA, Meghalaya, East Khasi Hills District, Umshing Mawkynroh, 25°36’51”N, 91°53’30”E, 1365 m a.s.l., under Pinus kesiya tree, 15 Jun 2022, N. Roy, B. Tanti & A.K. Dutta (GUBH 20322, holotype); Meghalaya, East Khasi Hills District, Umshing Mawkynroh, 25°36’43”N, 91°53’38”E, 1436 m a.s.l., under Pinus kesiya tree, 15 Jun 2022, N. Roy, B. Tanti & A.K. Dutta (GUBH 20321).
GenBank – GUBH 20322: OR775114 (ITS); GUBH 20321: OR775115 (ITS).
Notes – Russula pseudovirescens is easily recognized by its small to medium-sized pileus with a greenish-green to viridine-green cracked surface towards the margin, which turns red with guaiacol; free lamellae with occasionally one series of lamellulae; a sweet smell; basidiospores with ornamentations composed of small, amyloid, conical warts; hymenial cystidia mostly clavate to subclavate in shape with an obtuse apex; and a trichoderm type of pileipellis composed of sub-cylindrical to fusiform pileocystidia.
In the phylogenetic tree (Fig. 3), Russula pseudovirescens group together with other well-known members of R. subsect. Virescentinae (MLBS = 93%, PP = 1.00), confirming its systematic position within the subsection. The newly generated two Indian sequences of R. pseudovirescens cluster together (MLBS = 96%, PP = 0.99) with two earlier deposited sequences from China in the GenBank database after the name Russula aff. virescens (GenBank MT333229 and MT333231), suggesting all the sequences to be conspecific. However, there were no detailed descriptions available for Russula aff. virescens. Besides, the phylogenetic tree also confirms that the specimen is distinct from that of Russula virescens and is herein described as a new species (Fig. 3).
Apparently, Russula pseudovirescens can be confused with R. virescens, but R. virescens is primarily of European origin, whereas R. pseudovirescens is of Asian origin. Besides, R. virescens has a comparatively larger pileus (up to 125 mm diam.), sparsely forked and intervened lamellae, a larger stipe (40–90 × 20–45 mm), fusiform hymenial cystidia with a papillate or capitulate tip, and the absence of pileocystidia (Sarnari 2005).
Among other phylogenetically related taxa, Russula viridirubrolimbata differs from R. pseudovirescens by a larger pileus colored grass green at the center and darker red towards the margin and the presence of larger hymenial cystidia (78–107 × 8–10 µm) of fusiform to spindle-shaped (Deng et al. 2020). Russula parvovirescens has greenish brown to metallic bluish green or dark olive green pileus, the context of which discolors to ferruginous on exposure, some what larger basidiospores (mean of 7.5–8.0 × 6.4–6.5 µm vs. 6.4 × 6.0 µm in R. pseudovirescens), and longer hymenial cystidia (50–70 × 6–9 µm; Buyck et al. 2006).
Figure 1 – Russula pseudovirescens. a, b Basidiomata. c, d SEM photograph of basidiospores. Scale bars: a, b = 1 cm, c, d = 1 µm.
Figure 2 – Russula pseudovirescens (GUBH 20322, holotype). a Basidiospores. b Basidia. c Basidioles. d Hymenial cystidia near the lamella sides. e Hymenial cystidia on the lamella edges. f Pileocystidia with terminal cells near the pileus margin. g Pileocystidia with terminal cells near the pileus center. h Caulocystidia. Scale bars: a = 5 µm, b–h = 10 µm.
Figure 3 – Maximum Likelihood tree (-InL = 6185.166981) generated using GTR + I + G model of nucleotide evolution. Values to the left of ‘/’ are MLBS support, and those to the right of ‘/’ indicate Bayesian posterior probabilities (PP) support. MLBS values = 70% and PP values = 0.80 are shown above or below the nodes. Sequences generated for this study are in bold. Specimen voucher number, Country of origin and GenBank accession numbers are indicated after each taxon name.