Outline of the classification of European Russula according to Singer 1986 (The Agaricales in modern taxonomy)
Section Archaeinae (R. Heim) ...
Appearance much of that of sect. Plorantes. Gelatinous subcutis absent. Veil absent. Gills thick, unequal. Context hard and rigid, white, unchanging, mild. Spores very small, without a suprahilar spot. Macrocystidia and DC present. Spore print white.
Type : R. archaea Heim
No further subdivision
Section Plorantes Bat. ex Singer
Margin of pileus smooth, acute, appearance as in Lactarius sect. Albati. Gills unequal. Spore print usually pale coloured, rarely ochre to nearly yellow. Spores with distinct amyloid spot. Context hard and rigid, unchanging or slightly staining pink, esp. in gills. Pigment limited to a sometimes blue zone at the top of stipe and glaucescent gills. Gelatinous subpellis absent or present. Macrocystidia and DC present.
Type : R. delica
No further subdivision
Section Compactae Fr.
Cap with smooth, acute margin, pellis not sharply delimited from underlying context. Gills polydymous, with rather elongate basidia producing a white spore print. Spores without amyloid suprahilar spot. Context often bruising pink, also often blackening or at least grayish in age or on drying.
Type : R. nigricans
No further subdivision
Section Decolorantes (Maire) Singer
Cap with obtuse, not pectinate margin. Gills equal or with irregular lamellulae. Spore print variable. Spores with amyloid suprahilar spot. Context graying or blackening and often also staining pink or red, reddening with formalin, odor often of camembert, taste mild or somewhat acrid.
Type : R. decolorans
Subsections: Decolorantinae Maire, Vinosinae Singer
Section Ingratae Quél.
Definition: see classification Romagnesi 1987.
Subsections: Subvelatae (Singer), Foetentinae Melzer & Zvára (incl. Stirpes Granulata, Foetens, Pectinata), Farinipedes Romell, Felleinae Melzer & Zvára
Section Rigidae Fr.
Cap pruinate, (sub)velutinous, (sub)tomentose, areolate, squamulose to scurfy, more rarely glabrous, pellis not darkening with KOH, not yellowing or browning unless FeSO4 negative. Context not reddening with formalin, FeSO4 reaction positive, negative or insensitive, taste variable. Spore print pale to relatively dark (A-D), mostly with suprahilar spot.
Type : R. lepida.
Subsections: Cyanoxanthinae Singer, Lividinae Melzer & Zvára, Modestinae Singer, Subcompactinae Singer, Amoeninae Singer, Virescentinae Singer, Lilaceinae Melzer & Zvára, Roseinae Singer, Lepidinae Melzer & Zvára, Xerampelinae Singer, Pusillinae Singer
Pileus glabrous and viscid when wet, subpellis gelatinous, suprapellis never an epithelium or with virescens structure, pellis not pruinate, scurfy, etc..., unless spore print deeply coloured or taste very acrid and lamellae equal and not forked. FeSO4 never negative nor green, formaline negative, SV on dried stipe not bright red, pigment mostly not forming internal granules. Spore print from A to H, suprahilar spot always amyloid.
Type: R. emetica.
Subsections divided into 4 series:
1. spore print B-C, context staining yellow or brown, DC present or absent:
Melliolentinae Singer, Puellarinae Singer
2. Spore print A-E, mostly acrid, DC abundant:
Citrinae Romagn., Russula (incl. Stirpes Atropurpurea, Emetica), Sardoninae Singer, Sanguineae Melzer & Zvára (incl. Stirpes Luteotacta, Sanguinea, Pulchella)
3. Spore print D-E (-F), mild or slightly acrid in young gills, DC mostly present, often inconspicuous:
Betulinae Romagn., Integrae Maire
4. Spore print C to H, taste variable, context rarely yellowing or greying, DC present or absent, bitter or acrid, sometimes with primordial hyphae:
Olivaceinae Singer, Amethystinae Romagn., Chamaeleontinae Singer, Laetinae Romagn., Integroideae (Romagn.) Romagn., Firmiores Konr. & Maubl., Polychromae (Maire) Singer, Rubrinae Melzer & Zvára, Urentes Maire
This outline of the classification of European Russula in Singer 1986 omits exclusively exotic infrageneric taxa.
R. camarophylla is transferred from the exclusively tropical Delicoarchaeae Singer to Archaeinae, as indicated by Singer (loc. cit.) because of the presence of macrocystidia.
This is the last revision of a classification originally presented by Singer in 1932. Since that time, it has been undergoing several very important changes, especially under the influence of Romagnesi (1967). Singer subdivided the genus Russula at sectional and subsectional level, not at the subgeneric level, as in most recent European classification systems. Probably because of Singer's wider geographical perspective, the traditional subdivisions of subgenus Compactae in other European classifications are each considered important and different enough to constitute separate highest-level subdivisions of their own.
Another important difference between the proposed Russula classifications of Singer and the other modern classifications of European Russula, is the maintenance of section Rigidae as a group, principally based on macroscopic similarities between R. virescens - R. lepida. After 1951 and influenced by the work of Heim, Singer's delimitation of this group, corresponds very much to Romagnesi's subgenus Heterophyllidia + pale spored Incrustatula. Section Constantes, introduced in his first classification of Russula (1932), was a large rest-group in Russula of species groups with unchanging or yellowing context, and is redistributed in later classifications over sections Rigidae, Ingratae and Russula. The latter remained a very large group, although informally subdivided in 4 series, some of which correspond very well to certain subgenera of modern European classifications, example given: series 2 with subgenus Russula in Romagnesi (1987).
In general, it can be said that macroscopical characters are more important in the definitions of Singer's primary subdivision of Russula.