Russula paravioleipes G.J. Li & W.F. Lin, sp. nov.

Index Fungorum number: IF 558649; MycoBank number: MB 558649; Facesoffungi number: FoF 09207; Fig. 1

Etymology – Named after the close phylogenetic relationship with R. violeipes.

Holotype – HBAU 15001

Basidiomata small to medium sized. Pileus 28–46 mm diam., first hemisphere, then convex, applanate when mature, a tinge of brightly purplish red, daphne red (XXXVIII69′′), spinal red (XXVI71′), to eosine pink (I1d), sometimes faded to a paler orange reddish tinge of peach red (I5b) to strawberry pink (I5d), smooth, glabrous, slightly viscid when wet; margin not striate, rarely cracked, peeling 1/3–1/2 from the edge, rose colour (XII71b) to spinal pink (XXVI71′b). Lamellae adnate, 3–4 mm in height, 13–16 pieces per centimeter at edge, not forked, interveined, white (LIII), unchanging when bruised, lamellulae not observed.
Stipes 29–48×10–13 mm, central to subcentral, cylindrical, rugulose longitudinally, White (LIII), unchanging when injured, smooth, dull, not viscid when wet, slightly attenuate downward the base, first stuffed, hollow when old, annulus absent. Context 2–3 mm thick at pileus center, White (LIII), unchanging, taste mild, smell indistinct. Spore print pale cream (Romagnesi IIa–IIb).

Basidiospores [150/3/3] 5.5–7.1(–7.4) × 5.5–7.2 μm, Q = 1.02–1.27(1.31) μm, Q = 1.17 ± 0.07) μm, hyaline, subglobose to broad ellipsoid, rarely globose and ellipsoid, ornamentations amyloid, up to 0.7 μm in height, composed of long ridges interconnected as incomplete reticulum, isolated warts and short crests rare, suprahilar area plage distinct but inamyloid. Basidia 35–45×8–12 μm, cylindrical, subcylindrical to subclavate, rarely clavate four-spored, projecting 10–20 μm beyond hymenium, sterigmata 4–6 μm long. Hymenial cystidia 91–110×8–10 μm, hyaline, fusiform to subulate, sometimes clavate, unchanging in sulfovanillin (SV), apex acute. Pileipellis two layered; epipellis pseudoparenchymatous, ca. 150–200 μm deep, not clearly delimited from the spherocytes in context, terminal cells hyaline, subulate to bayonet-shaped, 57–85×5–8 μm, subapical cells 7–11 μm wide, pileocystidia absent; subpellis composed of somewhat gelatinized, densely interlaced, rarely branched and septate, hyaline hypha 3–6 μm wide. Stipitipellis a cutis, composed of parallel hyaline hypha 3–5 μm wide.

Habit and habitat – scattered in broad-leaved forest of Salix spp. and Cinnamomum camphora.

Material examined – CHINA, Zhejiang Province, Hangzhou City, Xihu District, Zhejiang University, Zijingang  Campus, 26 June 2019, W.F. Lin, 20190001 (HBAU 15001, holotype); ibid, 20190688 (HBAU 15002); ibid, 20190699 (HBAU 15003).

GenBank numbers – ITS = MN658517, MN658518, MN658519.

Notes – Russula paravioleipes is a member of subsection Amoeninae Buyck, subgenus Heterophyllidia Romagn., section Heterophyllae Fr. because of its absence of pileocystidia, long and subulate terminal hyphal cells of pileipellis, and empty hymenial cystidia not turning grey or black in Sulfovanillin (Sarnari 1998). The reddish tinged pileus is the remnants of “R. violeipes Quél.” in Park et al. (2013). The Korean “R. violeipes” can be differentiated from this new species for its areolate pileus surfaces and flushed stipes. However, the ITS phylogenetic analyses of this study cannot distinguish them (Fig. 2). Whether or not these Chinese and Korean specimens are of the same species still needs further analysis. The other members of subsection Amoeninae can be distinguished from R. paravioleipes (Fig. 1) by the following morphological characteristics: R. violeipes in Europe differs in its violaceous pileus and conspicuous hymenial cystidia 10–20 μm wide; R. amoenicolor Romagn. has purple, green, or variegated pileus, dark cream basidiospore print (IIc–IId), and a habitat of Quercus forest; R. amoena can be differentiated by its violaceous purple to olive greenish tinged pileus, and longer basidia 60–70×9–12 μm (Sarnari 1998); R. mariae differs in its soft pruinose pileus surface, and wider hymenial cystidia up to  12.5 μm (Adamčík et al. 2018).

Figure 1 – Russula paravioleipes (HBAU 15001, holotype). a Appearance of basidiomata on ground. b SEM photo of basidiospores. c Basidia. d Pseudocystidia. e Pileipellis. Scale bars: a=10 mm, c–e=10 µm

Figure 2 – Phylogram generated from maximum likelihood analysis based and ITS sequence data representing Russula paravioleipe and related species in Sect. Heterophyllae. Related sequences are retrieved from GenBank and UNITE databases. Forty-seven ITS sequences are included in the analysis comprises 546 characters after alignments. Russula dinghuensis (GDGM 45244), R. lotus (HKAS 76139), R. nigrovirens (HKAS 55222) and R. variata (TENN 067302) in Sect. Cyanoxanthinae (Subg. Heterophyllidia) are used as the outgroup taxa. Tree topology of the maximum likelihood analysis is similar to the Bayesian analysis. The
best RAxML tree with a final likelihood values of − 4326.910274 is presented. The matrix had 281 distinct alignment patterns, with 2.78% undetermined characters or gaps. Estimated base frequencies were as follows:
A=0.217569, C=0.256487, G=0.225771, T=0.300173; substitution rates AC=1.359519, AG=4.554062, AT=0.588669, CG=0.728567, CT=5.548012, GT=1.000000; gamma distribution shape parameter α=0.379017. Bootstrap values for maximum likelihood (ML) greater than 50% and posterior probability values greater than 0.90 (the rounding of values to 2 decimal proportions) from Bayesian-inference analysis are shown above the nodes. Type and ex-type are indicated in bold and the newly generated sequences are indicated in blue