Russula obscurozelleri Bazzicalupo, D. Miller & Buyck.
Index Fungorum number: IF553817 Facesoffungi number: FoF 03650
Etymology: refers to its similarity to R. zelleri.
Holotype: B. Woo BW803, (WTU, sub nr. F-038663)
Pileus 3–7(–12) cm diameter, fragile, young convex with inrolled margin, later plano-convex and often irregularly wavy–lobed, shallowly depressed but not becoming funnel-shaped in age, slightly striate at the margin; surface strongly viscid when wet, shining to dull when dry, peeling half way, variable in colour but nearly always, at least when young, with a very dark, sometimes near blackish centre, elsewhere dark purplish red to brownish red, dark pinkish red to brownish violet, later discolouring irregularly and developing paler yellowish tan to vinaceous pink spots. Lamellae adnate to almost subfree, equal or nearly so, rarely with occasional bifurcations, mostly normally spaced (ca. 1 L/mm) or somewhat more distant, with transversal anastomoses between gills, cream (of Woo specimens, ~25% recorded as white to pale cream) with maturity becoming distinctly yellowish (~75% of Woo specimens recorded as yellow to ochre); edge even, concolourous. Stipe mostly distinctly shorter than the cap diameter, typically widening toward the base, chalk white, sometimes with rusty stains, fragile. Context white, unchanging, sometimes with pinkish tones underneath the cap cuticle, reacting pale tan with FeSO4. Odor none. Taste mild in gills and flesh. Spore print cream to dark cream (of Woo specimens, ~15% Crawshay A–C, ~85% Crawshay D–F). Spores broadly ellipsoid, (5.9–)7.66–7.7–7.75(–10.7) × (5.3–)6.54–6.58–6.61(–7.9) µm, Q = 1.1–1.17–1.18(–1.4), ornamentation subreticulate, crested, with amyloid web–like interconnections and pointy warts at line intersections, up to (0.2–)0.64–0.65–0.66(–1.1) µm high; suprahilar spot present as a moderately amyloid patch. Basidia (38–)40–44.5–49(–61) × (9–)10–11–12(–13) µm, 4–spored, clavate; basidiola similar. Lamellar trama mainly composed of sphaerocytes, intermixed with cystidioid hyphae. Hymenial cystidia 70–85 × 8–10 µm, slightly clavate, sometimes capitate, reacting weakly to sulfovanillin (~80% grey and ~20% dark purple reaction). Pileipellis not sharply delimited from the underlying context of filamentous hyphae and sphaerocytes; suprapellis composed of loosely arranged hyphae. Pileocystidia in pileus terminal, measuring (27–)31–40–48.5(–53.5) × (4–)5–6–7.5(–9) µm, obtuse-rounded at the tips; contents refringent. Acidoresistant incrustations absent. Clamp connections absent in all parts.
Habitat and distribution: recorded with Pseudotsuga menziesii, Tsuga heterophylla, and Pinus contorta. The species seems to have a wide northern distribution in Canada including Newfoundland and Pacific Northwest (USA: California, Idaho, Oregon, Washington; Canada: British Columbia, Newfoundland).
Examined material: U.S.A., Oregon, Gerlinger Tree farm, 123.5˚W, 44.90083˚N, 215-600 m alt., 07 Nov 1992, B. Woo BW536, F-039388 (WTU), GenBank ITS2: KX813272; 08 Nov 1992, B. Woo BW535, F-039400 (WTU), GenBank ITS2: KX813271; Roseburg, Weandell Simpson, 123.35˚W, 43.25083˚N, 140 m, 19 Nov 1983, B. Woo BW383, F-039004 (WTU), GenBank ITS2: KX813159; Washington: Millersylvania State Park, 122.9083˚W, 46.91˚N, 67 m, 04 Nov 1984, B. Woo BW400, F-038523 (WTU), GenBank ITS2: KX813173; Olympia, Priest Point Park, 122.8961˚W, 47.06972˚N, 30 m, 24 Oct 1992, B. Woo BW532, F-039444 (WTU), GenBank ITS2: KX813268; Olympia, Tolmie State Park, 122.7762˚W, 47.120694˚N, 2 m, 18 Nov 1998, B. Woo BW803, F-038663 (WTU, holotype), GenBank ITS2: KX813466; Union Powerline – pole 93 S, 123.066667˚W, 47.250833˚N, 60 m, 21 Oct 1984, B. Woo BW390, F-038949 (WTU), GenBank ITS2: KX813164.
Notes: Russula obscurozelleri corresponds to Clade 7 in our phylogeny, to Woo sp. 50 in Bazzicalupo et al. (in press) and to UNITE SH DOI: https://plutof.ut.ee/#/datacite/10.15156/BIO/SH270408.07FU
Our phylogeny placed R. obscurozelleri with significant support as the sister to a clade including R. cessans, R. nauseosa, R. laricina, R. pseudotsugarum (clade 8, described below) and R. zelleri. R. obscurozelleri could easily be confused (both in micro- and macroscopic characteristics) with R. zelleri and R. pseudotsugarum in the Pacific Northwest region (Bazzicalupo et al. in press), and it also resembles the European R. laricina, R. nauseosa, and R. cessans (Romagnesi, 1967; Sarnari, 1998-2005). Russula cessans and R. laricina have not been recorded from the Pacific Northwest. The taxon ‘R. nauseosa’ has no matches to ITS sequences of species found in the Pacific Northwest. Host might distinguish R. obscurozelleri from R. zelleri. Russula zelleri was most often reported with Picea sitchensis or Picea engelmannii (Engelmann spruce), although sometimes in mixtures with Abies lasiocarpa (alpine fir) or Pinus contorta. R. zelleri caps were more likely to be brownish-greenish-yellowish. When R. zelleri’s caps were darker, they were more pinkish-brown to vinaceous or even purplish. When darker, R. zelleri caps had a mottled centre with paler yellowish-tan spots. Standard errors of the means of spore lengths across individual collections of R. zelleri, R. pseudotsugarum, and R. obscurozelleri overlapped and so spore measurements cannot be used for identification of individual collections. However the average spore length for R. zelleri was 8.9 µm, while the average spore length for R. pseudotsugarum was 8.1 µm, and for R. obscurozelleri, 7.7 µm.
Identical sequences were from Canada: Capilano Regional Park, Vancouver, BC (KX579784), Morne Trial, NL (KX579804); and West coast U.S.A.: California (EU248590, GQ221634) Washington (KJ748443, KJ748441, KJ748445). This taxon has also been collected in Newfoundland (KX579804) (Bazzicalupo et al. in press), which could indicate a northern distribution in Canada. Outside of the identical sequences listed above, the only other similar sequences in GenBank (as of March 2017) were more than 3% different.