Provisional key to subsection Virescentinae in the U.S.
This provisional key will help Russula amateurs to identify the species of subsection Virescentinae in North America, including several new taxa which are in the process of being described. You can proceed in the key by clicking on the numbers and also click on some names to check pictures (only for the species marked with an asterisk - *) or description of the species.
1. Cap pale yellowish brown to dark reddish brown or brownish grey, without green, pink or lilac tinges. ..... 8
1. Cap with limited to dominant vinaceous, pink or lilac shades (eventually with local green or brown colors). ..... 13
1. Cap whitish cream or with yellow pigments (species without pileocystidia in subpellis and SV-negative hymenial cystidia). ..... 16
2. Cap sometimes appearing smooth and somewhat pruinose, but actually obscurely and minutely areolate-scaly (easily observed with a hand lens as well as on dried material), sometimes only near margin, green to bluish green or metallic green, lacking pseudoparenchymatous layer (with dispersed extremities under the microscope).
2. Cap clearly areolate-scaly when mature, with well-developed pseudoparenchymatous layer. ..... 3
3. Dermatocystidia present at surface, but also in underlying subpellis (check real carefully and preferably at 1000 ×!). Hymenial cystidia distinctly graying or blackening in sulfovanillin. Fruit bodies medium-sized (ca 10 cm diam.) or more often relatively small (< 7 cm diam.) and fragile. ..... 4
3. Dermatocystidia present at cap surface only (if apparently lacking: see R. virescens EUR), not in subpellis or underlying trama. Hymenial cystidia insensitive or only weakly graying in sulfovannilin. Fruit bodies rarely small, but often rather stout and firm. ..... 6
4. Terminal cells in cap obtuse-rounded or at most papillate-ampullaceous and all ending at the same level (resembling some kind of continuous epithelium at cap surface). Hymenial cystidia varying from very few to dispersed. Cap typically rather small, mostly less then 7 cm diam., (although also but rarely up to 10 cm) and with large scales, in the center continuous and often discolored pale brown although sometimes also very dark, margin distinctly striate when mature (as opposed to R. virescens). Stipe often very slender (often length = cap diam.) and elegant.
4. Terminal cells in pileus locally (rarely dominantly) obtuse-rounded but mostly long and tapering and not all aligned at the same level, more like typical virescens-structure. ..... 5
5. Hymenial cystidia varying from dispersed to relatively abundant. Cap partly yellowish brown, usually with clear and often large squamae, context between scales smooth and squamae also with clear, abrupt outlines (not fibrillose at the border). Stipe generally short and stout. Majority of terminal cells rounded, either short and obtuse or long and tapering. (It needs to be verified if this species can be green!)
5. Hymenial cystidia widely dispersed. Cap green. Terminal cells nearly all long and tapering (more information is lacking)
6. Gills clearly not white, but with ochraceous tints (although spore print is pale cream). Cap dark olivaceous to almost brownish green, medium sized, densely covered with many small cottony looking pellicles because of fibrous nature of their borders. Pseudoparenchyma sometimes with very large but dispersed sphaerocytes near base of suprapellis and easily dispersed in squash preparations.
6. Gills whitish. Cap grass green, blue green or a soft, pale olive green. Pseudoparenchyma less easily dispersed in squash preparations; large sphaerocytes, when present, less widely dispersed. ..... 7
7. Cap grass green to greyish green, margin smooth to very shortly striate when old. Dermatocystidia apparently lacking near pileus surface (actually present but very poorly characterized, with hardly no contents), form of extremities very irregular. Presence in US not established.
7. Cap usually a soft, pale olive green (margin often striate… to be checked!). Dermatocystidia clearly present near pileus surface and with distinct contents, general aspect of extremities much more regular and homogeneous throughout cap surface.
7. Cap a soft olive green, composed of more regular, sometimes somewhat thick-walled extremities sitting on a continuous pseudoparenchymatous layer.
8. Cap surface scaly, under deciduous trees. ..... 9
9. Odour absent or weak. Cap with large, abruptly delimited scales, these generally pale brown to yellowish brown or ochraceous. Dermatocystidia present near surface, but also in subpellis (to be checked for real carefully and preferably at 1000 ×!). Hymenial cystidia distinctly graying or blackening in sulfovanillin. Fruitbodies often rather small (< 8 cm diam) ..... 10
9. Odour frequently very strong and nauseous, of rotting meat (road kill) or rotten cabbage. Cap either with large scales or with much more irregular, often small warty-scaly appearance, mostly dark brown to grayish brown. Dermatocystidia present near surface only (if apparently lacking: see Russula raymondii). Hymenial cystidia insensitive or only weakly graying in sulfovanillin. Fruit bodies rarely small. ..... 11
10. Cap a uniform, warm yellowish-reddish brown, dermatocystidia in subpellis numerous, terminal cells usually more or less cylindrical to subulate, longer than in Russula crustosa and often clitting together.
11. Cap with large, well delimited scales. Inodorous to slightly nauseous.
11. Cap with irregular warty-scaly appearance. Large sphaerocytes in subpellis. Odour often strong and nauseous. ..... 12
12. Odour always strong and nauseous.
12. Odour… nauseous? Do other species also have ochre gills? (Can this species be brown?)
13. Cap smooth or nearly so, no real pseudoparenchyma, entirely pinkish-red.
13. Cap generally with clear and large scales. ..... 14
14. Essentially bluish green to grayish green cap, but young sometimes with limited pinkish stains, especially near the margin. Terminal cells in pileus obtuse or at most papillate-ampullaceous and all ending at the same level (forming some kind of continuous layer like epithelium at cap surface). Hymenial cystidia varying from very few to dispersed.
14. Terminal cells in pileus locally (rarely dominantly) obtuse but mostly more or less elongated and not all aligned at the same level, more like typical virescens-structure. ..... 15
15. Cap pinkish red to orange (?) Hymenial cystidia staining with sulfovanillin.
15. Cap a mixture of very soft pastel colors, varying from soft lilac-purple to grayish pink, locally discoloured and buff to pale ochraceous or yellowish brown. Likely an exclusively southern taxon (?). Hymenial cystidia more or less weakly staining with sulfovanillin.
16. Cap more or less smooth, (according to the type description!), spores really elongate and irregularly minutely warty as in many Lactarius species, cystidia not staining in sulfovanillin.
16. Cap areolate-scaly, looking like a discoloured Russula virescens. Spores distinctly punctuate with isolate warts (if with chlorine smell and with brown squamae, compare R. chlorinosma Burl. (=? R. maculosa Murrill, =? R. subglauca Murrill).
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