Russula petersenii A. Ghosh & K. Das, 2017

Ghosh, Aniket & Das, Kanad, 2017, Russula (Russulaceae) in western Himalaya 1: Two new species from subg. Russula, Phytotaxa 323 (3), pp. 237-252 : 245-248

Russula petersenii A. Ghosh & K. Das sp. nov. Figs. 5 & 6

MycoBank:—MB 821642

Diagnosis:—Differs from other known species of this group by its white pileus with pale yellow to light yellow patches and concolorous stipe, white to yellowish white lamellae with 3 tiers of lamellulae, acrid taste, basidiospores with isolated obtuse warts (sparsely connected in places), differing shapes of apices of the cystidia and ITS sequence data.

Type :— INDIA. Uttarkhand , Bageshwar-district, Dhakuri, N 30°04.970’ E 79°55.134’, Alt. 2586 m a.s.l., on the soil under Rhododendron sp. in temperate forest, 2 August 2016, A. Ghosh, AG 16-1272 ; (holotype: CAL!; isotype: GUH!)

Etymology:—In honor of Dr. Ronald H. Petersen for his contribution to fungal taxonomy.

Description:— Basidiomata 33–42 mm in height, small- to medium-sized. Pileus 29–42 mm diam., hemispheric when young, convex to plano-convex or applanate when mature, center broadly depressed with age; margin decurved to plane with maturity, entire, slightly plicate-sulcate, viscid when moist then dry, peeling1/4 the length of the radius from the margin, chalky white (1A1) in color with pale yellow (4A3) to light yellow (4A4–4A5) irregular patches. Pileus context chalky white (1A1), up to 4 mm thick, unchanging when exposed, turning brownish red (8C6–8C8) to reddish brown (8D6–8D7) with guaiacol. Lamellae adnate to adnexed, rather crowded to crowded (9–12 per cm), chalky white (1A1) to yellowish white (1A2) at maturity, 2–4 mm in width, entire, concolorous edges, unchanging when bruised; lamellulae present in 3 series. Stipe 21–30 × 9–11 mm, equal to cylindric, central, dry, smooth, brittle, chalky white (1A1); turning brownish red (8C6–8C8) to reddish brown (8D6–8D7) with guaiacol; stipe context stuffed to hollow, chalky white (1A1), unchanging when exposed but turning brownish red (8C6–8C8) to reddish brown (8D6–8D7) and with guaiacol. Taste acrid. Spore print white (1A1).

Basidiospores (–5.5)6.84–7.47–8.1(–9) × (–5)5.84–6.38–6.92(–7) μm, (n = 60, Q = (–1)1.1–1.17–1.24(–1.36), subglobose to broadly ellipsoid, rarely ellipsoid; ornamentation of amyloid isolated obtuse warts (up to 0.9 μm high) only sparsely connected in places; suprahilar plage inamyloid, apiculus up to 2 μm high. Basidia 24–58 × 9–13 μm, 4-spored, cylindric to subclavate, sterigmata up to 8 μm long. Pleurocystidia 44–104 × 8–13 μm, abundant, cylindrical to subclavate with tapered base, capitate, appendiculate (appendages up to 7 μm long), blunt or rounded apex, emergent up to 32 μm; content dense, thick, crystalloid, turning greyish black with sulphovanillin. Lamellae edge fertile with basidia and cystidia. Cheilocystidia 52–68 × 7–9 μm, cylindric with mostly appendiculate, mucronate, blunt or rounded apex; content dense, thick, crystalloid, turning greyish black with sulphovanillin. Subhymenium up to 26 μm thick, pseudoparenchymatous. Pileipellis up to 140 μm thick, a trichoderm, composed of branched, septate, short terminal hyphae (3–4 μm diam.) with rounded or blunt apex and subterminal cells cylindrical to rectangular (3–5 μm diam.), incrustations present in some hyphae. Pileocystidia plentiful, 0–2 septate, cylindrical to subclavate (4–9 μm diam.) with rounded apex, content dense, turning greyish black with sulphovanillin, incrustations present in some pileocystidia. Clamp connections and laticiferous hyphae absent from all tissues.

Habitat and distribution:—Gregarious under Rhododendron sp. in temperate forest of Western Himalaya.

Specimen examined:— INDIA. Uttarkhand , Bageshwar district, Dhakuri, N 30°04.970’ E 79°55.134’, Alt. 2586 m a.s.l., on the soil under Rhododendron sp. in temperate forest, 2August 2016, A. Ghosh, AG 16-1272 (Holotype CAL!;

Isotype GUH!).

Notes:—The combination of macro- and micromorphological features including the presence of only a few incrusted pileocystidia, pilear hyphae in the epicutis and white spore print undoubtedly place R. petersenii in subg. Russula sec. Paraincrustatae subsect. Integrae ( Sarnari 1998) . Further, the placement of R. petersenii was confirmed with the molecular analyses. In the field Russula petersenii is distinct from other known species of this group by its white pileus with pale yellow to light yellow patches, concolorous stipe, chalky white to yellowish white lamellae with 3 series of lamellulae and acrid taste. Micromorphologically, it is separated from allied species by the presence of basidiospores with isolated warts which are only sparsely connected in places and the different types of cystidial apices (mostly appendiculate, capitate, blunt or rounded apex).

Based on a BLAST search of NCBIs GenBank nucleotide database, the closest hit using ITS sequence (AG 16- 1272) was Russula sp. HMAS 276795 [GenBank accession no. LT602963 ; query coverage 97%; Identity 98% and 0.0 E value] collected from China. Unfortunately there are no micro- and macromorphological details available for this collection in any published literature .

In subsect. Integrae, Russula integra (L.) Fr., originally reported from Europe, differs from the present species in having a brown to purple, green, yellow, etc. multicolored pileus, a white stipe with orange-red base, larger basidiospores (8.8–11.2 × 7.4–9) μm, an attenuate type of pilear hyphal tips and a dark yellow spore print ( Sarnari 2005; Kranzlin 2005). Three taxa which appear phylogenetically close to R. petersenii include R. integriformis Sarnari , R. velenovskyi Melzer & Zvára and Russula pusilla Peck (appeared in BLAST search & 0.0 E value). Russula integriformis , an European species, differs by its reddish brown, larger 50–80(130) mm diam. pileus, medium yellow spore print, basidiospores with low ornamentation (0.6 μm) and filamentous dermatocystidia [2.5–6(7) μm] ( Sarnari 2005) whereas, R. velenovskyi , originally reported from Europe, is distinct from R. petersenii by possessing bright red to copper red or vinaceous pink pileus with a low and broad umbo, ochre spore print and mild taste ( Sarnari 2005; Rayner 1985). Russula pusilla Peck (originally described from North America) differs from the present species in having larger basidiospores (7.5–9.5 × 5–7 μm) with isolated to catenulate warts being connected often with fine lines and an epicutis composed mostly of erect constricted hyphae ( Hesler 1960). Another taxon Russula seperina Dupain , an European species, differs from R. p etersenii by its violaceous red to brownish or green yellow pileus, context that turns black on exposure, pale ochraceous gills, and slightly larger basidiospores (7.8–9.7 × 6.5–8 μm) ( Rayner 1985; Sarnari 2005).

The presence of lamellulae in different ranks and the acrid taste of R. petersenii can also confuse it with these members of sect. Lactarioides ( Sarnari 1998) i.e. Russula pallidosopra , R. chloroides , R. delica . However, the present species differs from members of section Lactarioides by its small to medium sized basidiomata (33–42 mm in height), absence of short, stout stipe and presence of few encrusted pileocystidia and pilear hyphae in pileus cuticle.

Considering the white color of the basidiomata, the present species can be mistaken in the field with R. indoalba A. Ghosh, Buyck, A. Baghela, K. Das & R.P. Bhatt , R. kanadii A.K. Dutta & K. Acharya , R. leelavathyi K.B. Vrinda, C.K. Pradeep & T.K. Abraham , R. alboareolata Hongo and R. natarajanii K. Das, J.R. Sharma & Atri. However , R. indoalba , R. kanadii , R. leelavathyi (all originally reported from India) and R. alboareolata [described from Japan in association with Castanopsis ( Fagaceae ) and from Taiwan and Thailand in association with dipterocarps] differ from the present species in possessing a pileipellis which is typical of R. sect. Virescentinae [pileipellis bilayered; suprapellis composed of erect to suberect chains of cells, subterminal cells mostly rounded (inflated), terminal cells mostly, cylindrical to subulate; subpellis composed of horizontal, interwoven hyphae] and mild taste. Moreover, they all ( R. indoalba , R. kanadii , R. leelavathyi and R. alboareolata ) belong to subg. Heterophyllidia ( Hongo 1979; Vrindra et al. 1997; Watling & Lee 1998; Dutta et al. 2015; Hyde et al. 2016). Russula natarajanii , in subgen. Ingratula , is distinct by its strongly tuberculate-sulcate margin, mild taste, yellowish white spore print and slightly smaller basidiospores (6.5–8.8 × 5.8–7.1 μm) with low ornamentation (0.4 μm high), composed mostly of minute warts and ridges which form an incomplete reticulum ( Das et al. 2006).

Figures

FIGURE 5. Russula petersenii sp. nov. (AG 16–1272, Holotype). a–b. Fresh and dissected basidiomata in the field and at base camp; c–d. Radial section through pileipellis showing elements; e–f. Transverse section through lamellae showing pleurocystidia; g. Transverse section through lamellae showing cheilocystidia; h–i. Image of basidiospores under SEM. Scale bars: b = 40 mm; c–g = 10 μm; h–i = 2 μm. Photographs by A. Ghosh.

FIGURE 6. Russula petersenii sp. nov. (AG 16–1272, Holotype) a. Dissected basidiome; b. Radial section through pileipellis; c. Basidiospores; d. Basidia; e. Pleurocystidia; f. Cheilocystidia. Scale bars: a = 10 mm; b–f = 10 μm. Drawings by A. Ghosh.