Russula indoalba

Russula indoalba A. Ghosh, Buyck, A. Baghela, K. Das & R.P. Bhatt

Index Fungorum number: IF552159 Facesoffungi number: FoF02471

Etymology: referring to white basidiomata growing in India

Holotype: CAL 1328.

Basidiomata 70–100 mm. in height. Pileus 30–95 mm. in diam., broadly convex when young, gradually planoconvex
to applanate with depressed center, finally uplifted at maturity; margin decurved to plane, entire, tuberculately striate; surface dry, viscid when moist, cracked-areolate when mature, white (1A1–2A1) with greyish-yellow (4B4–4B6) to pale yellow (3A3) spots at the center; lemon-yellow or pale yellow to pastel yellow (1A3–1A4) with KOH; cap context white (1A1–2A1), lemon-yellow or pale yellow to pastel yellow (1A3–1A4) with KOH. Lamellae adnexed to almost free with age, equal, subdistant to close (7–10/cm), forked near the stipe apex, white (1A1–1A2), with entire, concolourous gill edges. Stipe 20–65 × 10–23 mm., subclavate, central, dry, smooth, white (1A1–2A1), lemonyellow or pale yellow to pastel yellow (1A3–1A4) with KOH; context stuffed, becoming hollow with age, white (1A1–2A1), greyish-orange (5B4–5B5) with FeSO4, unchanging with guaiacol and NH4OH. Taste mild. Odour indistinctive. Spore print yellowish-cream. Basidiospores 5.5–7.42–9.5 × 5.5–6.4–8 um (n= 50, Q = 1–1.16– 1.36), subglobose to broadly ellipsoid, rarely ellipsoid; ornamentation amyloid, composed of short (0.3–0.5 um) and long (0.7–1 um) conical to cylindric warts, mostly connected to form incomplete reticulum, few isolated, apiculi up to 2 um high; suprahilar spot not amyloid. Basidia 45–60 × 9–13 um, 4-spored, cylindrical to subclavate, sterigmata up to 5 um long. Pleurocystidia 47–90 × 8–16 um, subclavate to clavate with capitate, moniliform, appendiculate and rounded apex, emergent up to 38 um beyond the basidiole tips. Cheilocystidia 55–68 × 6–8 um, cylindrical to subclavate with appendiculate apex. Subhymenium layer up to 26 um thick, pseudoparenchymatous. Lamellar trama consists predominantly of sphaerocytes. Gill edges fertile. Pileipellis up to 120 um thick, distinctly divided into suprapellis and supellis; subprapellis composed of erect to suberect chains of 3–6 rows of cells; subterminal cells 8–20 × 6–18 um, mostly rounded (inflated), ellipsoid; terminal cells mostly, cylindrical to subulate; subpellis composed of. horizontal, interwoven hyphae. Pileocystidia rare, one-celled, slender, thin-walled, up to 7 um wide, dispersed as terminal cells in the suprapellis.

Habitat and distribution: Under Quercus sp. in mixed forests dominated by Quercus, Rhododendron, Abies and Cupressus.

Material examined: INDIA, Uttarakhand, Rudraprayag district, Baniyakund, alt. 2630 m, N3028.9140 E7910.8540, 1 September 2014, A. Ghosh, AG 15-541 (GUH); ibid., 14 July 2015, A. Ghosh, AG 15-628 (CAL 1328, holotype); ibid., A. Ghosh, 16 July 2015, AG 15-661 (GUH); ibid., 1 August 2015, A. Ghosh, AG 15-797 (GUH).

Notes: Russula indoalba which is characterized by white pileus with greyish-yellow to pale yellow spots at center, tuberculately striate and wavy to interrupted pilear margin, equal gills, yellowish-cream spore print and mild taste is a typical member of Russula subg. Heterophyllidia sect. Virescentinae. In the field Russula kanadii A.K. Dutta & K. Acharya (also reported from India) appears to be quite similar to the present taxon. However, R kanadii has a white spore print (1A1), smaller basidiospores [(4.5)–5.5–5.7–6.5 (–7) × (4.5)–5.3–5.5(–6) um] and grows at very low altitudes (56 m) being ectomycorrhizal with dipterocarps, viz. Shorea robusta (Dutta et al. 2015). Russula alboareolata Hongo, described from Japan in association with Castanopsis (Fagaceae), but also reported from dipterocarps in Taiwan (Watling and Lee 1998) and Thailand is also very similar to R. indoalba but has smaller basidiospores 6.5–8.5 × 5.5–7 um (Hongo 1979). Phylogeny shows that R. alboareolata is genetically closer to R. kanadii than to our new species or to the other Virescentinae. Furthermore, the phylogeny also suggests, although without support, that R. indoalba is basal to the core group of Virescentinae (R. virescens and allies) suggesting a migration from India via Asia to both Europe and North America. All species in this core-group differ from other Virescentinae such as those belonging to the R. crustosa–R. mustelina lineage and also R. parvovirescens Buyck et al. (Buyck et al. 2006) in the absence of dermatocystidia in the lower subpellis (Buyck, http:// www2.muse.it/russulales-news/id_virescentinae.asp).