Russula sribuabanensis

Russula sribuabanensis Paloi, Suwannarach N. & Kumla J.

MycoBank number: MB 848803

Basidiomata medium- to large-sized. Pileus 25−105 mm diam., hemispherical to convex at early stage, becoming broadly convex, applanate to plano-concave with a central depression when mature, surface pruinose, viscid (25B2‒26B2), greenish white (25A2) at center, becoming fed toward margin gray (26B1), greenish white (25A2) to greenish gray (25B2), no change after bruising, turned light yellowish to yellowish brown with 10% KOH; margin incurved, regular when young, becoming striate, cracked, sometime wavy at maturity. Lamellae adnate to narrowly adnate, up to 6 mm wide, regular, white (1A1) to cream; edge even, concolorous; lamellulae none, sometimes if present, one in a row. Stipe central, 45−70 × 7−19 mm, cylindrical, tapered toward the base, sometimes curved, smooth, white (1A1), turned light yellowish after bruising, light yellowish or yellowish brown with 10% KOH; context firm, white (1A1), becoming very light yellowish after exposed to air. Odor unknown. Taste mild. Spores print cream. Basidiospores 6.2−7.4−8.2 × 5.6−6.2−7.2 μm, Q =1.0−1.1−1.2, sub-globose to sub-ellipsoid, ornamentation amyloid, composed with 0.15-0.25 low to 0.3−0.4 μm high lines connected with each other and produced a complete reticulate ornamentation, suprahilar spot, inamyloid to weak amyloid. Basidia 35.5−52 × 6.5−9 μm, sub-clavate to subcylindrical, thin-walled, hyaline, oil granules present with 5% KOH, 4-spored, sterigmata up to 4 μm long. Lamellae edge composed with numerous cystidia, sterile. Subhymenium pseudoparenchymatous. Hymenial cystidia near gill edge, 61−109 × 8−14 μm, subclavate to sub-cylindrical with appendiculate to moniliform or pointed apex, thin-walled, hyaline, oil granules present with 5% KOH, same as gill side, up to 53 μm long projection. Pileipellis orthochromatic in cresyl blue, context composed with sphaerocytes; subpellis 250−350 μm deep, composed with more or less loosely arranged hyphae, 2.5−4 μm broad, thin-walled , hyaline, sometimes oil granules present when viewed with 5% KOH; suprapellis 49−90 μm deep, gelatinized, composed tightly arranged suberect to repent hyphal end, 21−63 × 3.5−5.5μm, thin-walled, hyaline, sometimes fills with cytoplasmic contains, obtuse to pointed apex, subterminal cell 8.5−20 × 5.5−10 μm, globose, sub-globose to ellipsoid, thin-walled, hyaline. Pileocystidia absent or very rarely present in margin,frequently found in center, 30−43 × 4−5.5 μm, clavate to cylindrical with mucronate, moniliform to obtuse apex, thin-walled, hyaline, fill with cytoplasmic contains, sometimes long cystidia observed 4.5−6.5 μm wide. Stipitipellis composed with tightly arranged, terminal hyphal, 2.5−4 μm broad, thin-walled, hyaline, pointed or obtuse apex; subterminal cell sub-globose to ellipsoid. Caulocystidia 20.5−41× 3−5.5 μm, sub-clavate to obtuse apex, very rare appendiculate or mucronate apex, thin-walled, hyaline, fill with cytoplasmic contains, sometimes very long, 3.5−6 μm in diam. Clamp connection absent in all tissue.

Ecology and distribution: Solitary, growing in a forest dominated by trees of Shorea spp. (Dipterocarpaceae). Known only from the type locality in Northern Thailand.

Additional material examined: Thailand, Lamphun Province, Mueang Lamphun District, Sribuaban Subdistrict,18°32′11″ N; 99°07′29″ E, elevation 414 m, 25 August 2022, S.N. Suwannarach and J. Kumla (SDBR-CMUNK1760). GenBank accession numbers OQ957228 (nrITS), OQ968132 (nrLSU).

Fig. 1 A combined (nrITS+nrLSU) phylogram derived from maximum likelihood analysis of 62 taxa. Three Russula species, R. nigricans, R. dissimulans, and R. camarophylla were used for rooting purposes. The numbers above branches represent maximum likelihood bootstrap percentages (right) and Bayesian posterior probabilities (left). Bootstrap values ≥ 75% and Bayesian posterior probabilities ≥ 0.90 are shown above the branches. The scale bar represents the expected number of nucleotide substitutions per site. Type sequences highlighted in bold front. Newly reported species in this study are highlighted (blue front) and corresponding species pictures are provided.