Russula rubescens Beardslee, Mycologia, 1914

Adamčík, Slavomír, Jančovičová, Soňa & Buyck, Bart, 2015, Type-studies in American Russula subsection Decolorantes (Russulales, Basidiomycota), part II., Phytotaxa 231 (3), pp. 245-259 : 252

Russula rubescens Beardslee, Mycologia 6: 91. 1914. Figs. 19–27

Original description:— Pileus convex, finally expanded and depressed, 5–8 cm. broad; surface red, margin paler, fading with age, thin, striate; context mild to the taste; lamellae rather close, white, adnate, forked, especially at the base; spores pale-yellow, subglobose, 7–9 μm, rough, echinulate; cystidia large, numerous, 50–64 × 10–12 μm; stipe white, at length becoming cinereous without and within, often blackening with age or in drying, quickly becoming red and then black when wounded, stuffed, becoming hollow.

This species seems especially well marked. The reddening of the stipe when scraped is seen in certain members of the Compactae , but a red species which has this character is novelty. It suggests in some ways R. depallens Fries , which seems to be a puzzle to European mycologists. It is believed by them, however, to be different from that species. As it grows, I find the stipe always becoming blackish within and without at the base.

Spores subglobose to shortly ellipsoid, (7.3–)7.7–8.4(–8.7) × (5.7–)6.1–6.7(–6.9) μm, average 8 × 6.4 μm, Q=(1.17–)1.21–1.29(–1.32), average Q=1.25, having distant [3–5(–6) spines in a 3 μm circle on spore surface] conical spines, measuring (0.6–)0.8–1.1 μm high, with occasional line connections [0–3(–5) in the circle] or fused in pairs or triplets [0–2 fusions in the circle], with frequently isolated spines; suprahilar plage amyloid, large. Basidia (29–)32–38 × 8.5–12 μm, average 34 × 10 μm, 4-spored, clavate; basidioles cylindrical, then narrowly clavate. Subhymenium pseudoparenchymatic. Lamella trama with large sphaerocytes. Hymenial cystidia widely dispersed to dispersed, ca. 300–400/mm 2, measuring (39–)56–74(–77) × (8–)9–11(–12) μm, average 66 × 10 μm on gill faces and smaller near the gill edge, clavate or fusiform, pedicellate, some with (3–)4–7(–9) μm long appendage, thin- to thick-walled, with heteromorphous, banded contents that turn reddish gray in sulfovanillin. Marginal cells well differentiated, moniliform, flexuous or with apical constriction, measuring (17–)22.5–33(–35) × 3–4.5 μm, average 28 × 4 μm, mixed with cheilocystidia. Pileipellis orthochromatic in Cresyl Blue, sharply delimited from the underlying sphaerocytes of the context, distinctly divided in a 40–75 μm deep, strongly gelatinized suprapellis of erect or ascending hyphal ends and a shallow, 20–30 μm deep subpellis of less gelatinized, narrow, dense and irregularly oriented hyphae. Acidoresistant incrustations not observed, but contents of pileocystidia staining red after the Carbol fuchsin treatment. Hyphal extremities near the cap margin with terminal cells measuring 15–29(–38) × 2–3.5 μm, average 23 × 3 μm, cylindrical or subulate, with constricted tips, slightly moniliform and flexuous, even more slender and flexuous in cap centre; subterminal cells mostly branched, nodulose, often with lateral branches, equally wide or slightly wider. Pileocystidia near the cap margin mostly one-celled but in cap center often septate, some arising from deep in cap trama, with terminal cells measuring (28–)40–130(–200) × 4–6 μm, average 85 × 5 μm, narrowly clavate, with long tapering basal part, in the cap center shorter and often wider and broadly clavate, continuing as cystidioid hyphae in subpellis and cap trama, with heteromorphous, banded contents distinctly graying in sulfovanillin, thin-walled, without incrustations. Clamp connections absent in all parts.

Examined material:— UNITED STATES. North Carolina.Asheville, August 1913, Beardslee (NY00760742, lectotype, here designated).

Commentary:— Beardslee (1914) did not refer to any collection in the protologue of R. rubescens , but his publication deals with agarics from Ashville, North Carolina. There is only one collection by Beardslee deposited in the herbarium NY that was collected in Ashville, NC in 1913 and this collection is labelled as possible syntype and was studied and annotated by Hesler and Bills and most likely also referred to as the type by Singer (1947). Since we know of no other authentic material collected by Beardslee from the type collecting area before 1914 this apparently represents authentic material and we are designating it here as the lectotype.

Because of its graying context and sulfovanillin positive pileocystidia, this species undoubtedly belongs in subsect. Decolorantes and was always placed there, although Singer (1947) thought it identical with R. obscura ( Romell 1891:179) Peck (1907: 94) in the sense of Kauffman (1918: 148) and considered his own “ R. kauffmaniana ” Singer (1939: 258) a later (and invalid) synonym ( Singer 1951 and after).

The spore ornamentation of R. rubescens showing frequently isolated spines separate it easily from R. magna , R. cinerascens and R. burkei , but is very similar to the spore ornamentation of R. rubriceps . There are some differences between the types of R. rubescens and R. rubriceps but more collections or molecular data are needed to correctly appreciate these: in the former pleuro- and cheilocystidia are larger and without appendage, marginal cells are not differentiated and terminal cells of hyphal extremities near the cap margin narrow at the tip.

Figures

FIGURES 19–21. Russula rubescens (lectotype). 19. Pileocystidia near the cap margin (right) and near the cap centre (left). 20. Hyphal extremities in the cap center. 21. Hyphal extremities near the cap margin. Contents of cystidia are represented as observed in Congo Red for some elements only, the others are simply filled with dots to indicate their cystidial nature. Scale bar equals 10 μm. Drawings by S. Jančovičová.

FIGURES 22–27. Russula rubescens (lectotype). 22. Basidia. 23. Basidioles. 24. Marginal cells. 25. Basidiospores in Melzer’s reagent. 26. Cheilocystidia.27. Pleurocystidia.Contents of cystidia are represented as observed in Congo Red for some elements only, the others are simply filled with dots to indicate their cystidial nature. Scale bar equals 10 μm, but only 5 μm for spores. Drawings by: S. Jančovičová.