Russula nigrovirens Q. Zhao, Y.K. Li & J.F. Liang, 2015

Zhao, Qi, Li, Yang-Kun, Zhu, Xue-Tai, Zhao, Yong-Chang & Liang, Jun-Feng, 2015, Russula nigrovirens sp. nov. (Russulaceae) from southwestern China, Phytotaxa 236 (3), pp. 249-256 : 252-255

Russula nigrovirens Q. Zhao, Y.K. Li & J.F. Liang , sp. nov. Fig. 2

MycoBank MB 810879

Holotype: CHINA, Yunnan Province, Yulong County, Laojunshan, in subalpine forest dominated by Picea sp. , Rhododendron sp. , Sorbus sp. and Abies sp. , elev. 3400 m, 16 August 2008, Qi Zhao 8240 ( HKAS 55222! GenBank accession: KP 171173).

Etymology: “nigrovirens ” refers to the deep green color of the pileus.

Pileus 3–10 cm diameter, first hemispherical, becoming convex or plano-concave with a slightly depressed center, often subinfundibuliform with age; margin incurved, surface viscid when moist, shiny in fresh and dry conditions, cracking and broken into small patches, patches crowded in the center, with smaller patches towards the margin; green white (26 A 2) to grayish green (27D5) with patches of dull green to deep green (26 E 4) to leaf green (29D5–7) when dry; suprapellis readily peeling even to the center, unchanging in color when bruised. Lamellae adnate, crowded,

rarely forking near the stipe, with scattered lamellulae, white, cream yellow when dried, unchanging when bruised or with FeSO 4. Stipe 6–10 × 1.0– 2.5 cm, cylindrical, slightly attenuate towards the base, subglabrous, smooth, dry, white to whitish, spongy inside. Context 5–8 mm thick, white to cream when dry, without color changing when bruised and treated with FeSO 4. Annulus absent. Odour indistinct. Taste mild. Spore print whitish.

Basidiospores [100/5/5] (6) 6.5–8.5 (9.5) × (5.5) 6–8 (8.5) μm [ Q = 1–1.28 (1.33), Q av = 1.17 ± 0.09), globose to subellipsoid; ornamentation amyloid; warts bluntly conical to subcylindrical, not exceeding 0.6 μm in height, isolated or connected with irregular lines or ridges, not forming a reticulum; suprahilar plage indistinct, not amyloid; hyaline in 5% KOH. Basidia 45–75 × 9–14 μm, 4-spored, rarely 2-spored, sterigmata up to 8 μm long, narrowly clavate to clavate, slightly bulbous towards upper third. Lamellar trama mainly composed of nested sphaerocytes (21–38 × 19–30 μm) surrounded by connective hyphae. Cheilocystidia 46–55 × 6.5–8.5 μm, rare, narrowly clavate to clavate with rounded or mucronate apex, contents granular. Pleurocystidia 47–72 × 7–10 μm, abundant, projecting 10–20 μm beyond hymenium, slender, clavate to subfusiform, apex obtuse, bluntly acuminate or mucronate, with abundant granular contents, dark grey in SV. Marginal cells 9–27 × 3.5–5 μm, cylindrical to narrowly clavate, hyaline. Pileipellis metachromatic in cresyl blue, consisting of interwoven, ascending to repent hyphae (2–5 μm diameter), often ramifying, septate; terminal elements 15–46 × 2.5–5 μm, apices obtuse, sometimes attenuate, with a distinct granular content; pileocystidia similar to terminal cells, but only present in suprapellis, apex mucronate or subterminally constricted, always one-celled, 18–62 × 3–6.5 μm, negative in SV. Stipitipellis not well-developed, cutis composed of thin-walled, septate, cylindrical hyphae 3–5 μm diameter; caulocystidia numerous, crystalline contents, 29–96 × 3.5–6.5 μm, subcylindrical to narrow clavate. Clamp connections absent.

Habitat and distribution: gregarious or scattered in forests dominated by Picea sp. , Rhododendron sp. , Sorbus sp. and Abies sp. Known only from high altitude localities in southwestern China.

Additional specimens examined: CHINA, Yunnan Province: Yulong County, Gaomeigu , elev. 3000 m, 16 August 2008, Qi Zhao 841 ( HKAS55042 ! GenBank accession: KP171174 ) ; elev. 3000 m, 19 August 2008, Qi Zhao 8248 ( HKAS55230 !) ; elev. 3000 m, 20 July 2008, Qi Zhao 844 ( HKAS55045 ! GenBank accession: KP171175 ) ; Dali County, Cangshan , elev. 3600 m, 12 August 2010, Qi Zhao 826 ( HKAS69567 ! GenBank accession: KP171176 ) .

Discussion

Russula nigrovirens is well distinguished by the non-striate pileus with dull green patches, incurved margin, globose to subellipsoid basidiospores with bluntly conical to subcylindrical warts isolated or connected with irregular lines or ridges, white spore print, and large, clavate basida. Considering the combination of its deep green pileus, white stipe,

context negative with FeSO 4, inamyloid suprahilar plage, one-celled, SV-negative pileocystidia, white spore print, and mild taste, R. nigrovirens is placed in Russula subgenus Heterophyllidia subsection Cyanoxanthinae ( Singer 1986,

Romagnesi 1987, Sarnari 1998).

Bayesian and RAxML phylogenetic analyses showed that R. nigrovirens was different from known Russula species for which ITS sequences were available. It is closely related to the European species R. cyanoxantha and the North American species R. variata . However, the latter two species have variable pileus color, context that tends to change to green with FeSO 4, and shorter basidia. In addition, R. cyanoxantha differs from R. nigrovirens in its basidiospore ornamentation that is never connected with fine lines, and narrow hymenial cystidia (≤7 μm).

Ecologically, R. cyanoxantha invariably grows in temperate to boreal areas ( Romagnesi 1967, Phillips 1981, Bon

1988) while R. nigrovirens grows only in subalpine area. Russula variata , described in forests of oaks and other hardwoods from eastern North America, is distinguished by its smooth pileus, soft, repeatedly forked lamellae, and acrid context ( Phillips 1981, Bon 1988). Russula cutefracta Cooke from United Kingdom, which was recognized as

R. cyanoxantha f. cutefracta by Sarnari (1998), resembles R. nigrovirens in cracking of the cuticle. However, it has a variably colored pileus that is sometimes violet, a purple tinted stem, indistinctive cystidia, and smaller basidia ( Bon

1988, Sarnari 1998). Russula anisopterae Buyck & E. Horak (1999) , described from Papua New Guinea, has an olive coloured, smooth pileus with an upturned margin, a hollow-chambered stipe, isolated basidiospore ornamentation,

shorter basidia, and undifferentiated marginal cells ( Buyck & Horak 1999). Russula langei Bon , described from

France, differs in having a violaceous colored, smooth pileus, a stipe with a tinge of lilac, context that quickly turning green with FeSO 4, and smaller basidia ( Bon 1988, Sarnari 1998).

In the field, R. nigrovirens is often confused by local residents with the European species R. virescens . However,

the ITS sequences clearly distinguish the two species as they fell into two distinct clades ( Fig. 1 ). Russula virescens differs from R. nigrovirens by its cracked pileus with tuberculate-striate margin, pale yellow lamellae, white stipe turning pale grayish yellow when injured, broadly elliptic basidiospores with the ornamentation forming a partial or complete reticulum, and smaller basidia (≤50 μm) ( Romagnesi 1967, Shaffer 1970). Russula parvovirescens Buyck et al. (2006) , from the United States, also has green patches on the pileus but a greenish brown to metallic bluish coloured pileus with slightly striate margin, thin flesh that turns brownish orange with FeSO 4, orthochromatic pileipellis in cresyl blue, pale cream spore print, basidiospore ornamentation forming an incomplete network, and shorter basidia

(≤45 μm; Buyck et al. 2006), while R. griseoviridis McNabb (1973) , described from New Zealand, differs in having greyish green pileus with greyish red colouration, pileus margin that is often radially split, free to adnexed lamellae, basidiospore ornamentation forming an incomplete reticulum and smaller basidia (35–53 × 6.5–11 μm; McNabb 1973).

Several species in Subgenus Heterophyllidia with a green pileus described from the Himalayan Mountains and southwestern China are similar to R. nigrovirens . Russula sikkimensis described from India ( Das et al. 2013), has a smooth pileus, context turning pale yellow with FeSO4, partially reticulate basidiospore ornamentation, and smaller basidia (40–54 × 7.5–10 μm). Russula atroaeruginea ( Li et al. 2013) differs from R. nigrovirens in a blackish green tinged pileus without patches, context turning pale yellowish with age, smaller basidia (40–48 × 9–11 μm), and absence of cheilocystidia ( Li et al. 2013). Russula viridella var. yunnanensis Singer (1935) is distinguished by a green pileus with purple colouration without patches, acrid context, cream spore print, smaller basidia (≤50 μm), and pleurocystidia with an obtuse or acuminate tip ( Singer 1935).

Figures

FIGURE 1. The best RAxML likelihood tree (–In L 4392.662321) based on the ITS dataset. Support values in bold type are RAxML likelihood bootstrap (≥70%). Values in normal type are Bayesian posterior probabilities (≥0.95). Classification followed by Sarnari (1998).

FIGURE2.Russulanigrovirens(HolotypeHKAS55222!).ABasidiomata;BBasidiospores;C Basidia;DCheilocystidia;EPleurocystidia; F Marginal cells; G Pileipellis; H Pileocystidia; I Caulocystidia.