Russula hypofragilis Bazzicalupo, D. Miller & Buyck.
Index Fungorum number: IF553816 Facesoffungi number: FoF 03649
Etymology: refers to the resemblance to taxon R. fragilis.
Holotype: BW920 (WTU, sub nr. F-038403)
Pileus 4–11.5 cm diameter, convex, then becoming deeply concave and with striate margin; surface smooth, purple, purplish red, vinaceous to grayish olive. Lamellae adnate, normally spaced (ca 1 L/mm), equal or with some rare lamellulae and none to few bifurcations, white to cream coloured (of Woo specimens, ~90% recorded for ‘white’; ~10% for ‘cream’). Stipe less or equal to cap, cylindrical, mostly firm and solid. Context white, unchanging with age or on injury, turning tan to grey-pink with FeSO4. Odor none. Taste mild (mostly) to slightly hot (of Woo specimens, ‘hot’ for flesh in ~33%; for gills, ~50%). Spore print very pale (of Woo specimens, ~90% Crawshay A, ~10% Crawshay B). Spores ellipsoid, (7.1–)8.41–8.45–8.49(–10.2) × (5.5–)6.71–6.73–6.67(–8.1) µm, Q = (1.1–)1.25–1.26–1.3(–1.5); ornamentation subreticulate, composed of amyloid, conical warts, (0.2–)0.92–0.94–0.95(–1.6) µm high, sometimes slightly curved at the tips, interconnected by web–like patterns or thin lines between warts; suprahilar spot present as a patch, but not highly amyloid. Basidia (33.5–)39–44–49(–60.5) × (8–)9.5–11–12(–13) µm, 4-spored, stout and clavate with swollen top; basidiola similar. Lamellar trama mainly composed of sphaerocytes, intermixed with cystidioid hyphae. Hymenial cystidia 80–95 × 8–10 µm, broadly clavate to fusiform, thin-walled, SV+ and turning dark purple in sulfovanillin. Pileipellis not sharply delimited from the underlying context of filamentous hyphae and sphaerocytes; suprapellis composed of loosely arranged, branching hyphal terminations, with cylindrical terminal cells. Pileocystidia at pileus surface measuring (20–)21.5–22–23.5(–30.5) × (2.5–)5–6.5–7.5(–8.5) µm, occasionally constricted at the tips; contents refringent, continuing as cystidioid hyphae with refractory contents in subpellis and trama. Acidoresistant incrustations absent. Clamp connections absent in all parts.
Habitat and distribution: consistently reported with Abies, sometimes mixed with Pinus contorta, Picea stichensis, Pseudotsuga menziesii, and Tsuga heterophylla. Only known from the Pacific Northwest (USA: Washington; Canada: British Columbia).
Examined material: U.S.A., Washington, Lake Kachess, Road 4934, 121.25˚W, 47.366944˚N, 710-800 m alt., 13 Oct 1996, B. Woo BW649, F-038961 (WTU), GenBank ITS2: KX813353; ibidem, Sloan Creek, 121.287778˚W, 48.0575˚N, 630 m alt., 04 Oct 1992, B. Woo BW519, F-039439 (WTU), GenBank ITS2: KX813256; B. Woo BW525, F-039441 (WTU), GenBank ITS2: KX813260; ibidem, 03 Oct 1993, B. Woo BW548, F-038825 (WTU), GenBank ITS2: KX813283; ibidem, 19 Sep 1999, B. Woo BW814, F-038713 (WTU), GenBank ITS2: KX813476; ibidem, 23 Sep 2001, B. Woo BW920, F-038403 (WTU, holotype), GenBank ITS2: KX813553.
Notes: Russula hypofragilis corresponds to Ben Woo Clade 2, to Woo sp. 28 in Bazzicalupo et al. (in press) and to UNITE SH DOI: https://plutof.ut.ee/#/datacite/10.15156/BIO/SH297355.07FU
Our phylogeny placed R. hypofragilis as sister without support to R. montana, in a well supported clade together with R. aquosa and R. phoenicea. As is evident from the above description, this new species could be mistaken for R. phoenicea, given macromorphology and the size and form of its microscopic features. The European R. aquosa, as yet unknown from the Pacific Northwest, is also similar morphologically and would be difficult to distinguish without sequencing. Russula hypofragilis was always recorded in the presence of Abies, while its look-alike, R. phoenicea, was usually with Pseudotsuga. Russula hypofragilis is common and may have been recorded as R. atropurpurea in species lists in the Pacific Northwest.
Geographically, samples with identical ITS2 sequences to R. hypofragilis have only been recorded from the Pacific Northwest to date [Canada, British Columbia; GenBank nrs HQ604847, KP889642), Campbell River, Vancouver Island, BC (GenBank nrs EU597058, KP406576)]. As of March 2017, other sequences with 1% difference have been recorded from Tennessee (GenBank nrs HQ022216, KF359620, KF359619), and a 3% difference will hit collections attributed to R. montana in Europe as well as in the United States and Canada.