The spore-print varies, depending on the species involved, from white to deep ochre and individual spores are covered in a coarse ornamentation which is composed of isolated warts or warts interconnected by raised lines, or mixtures of both. The ornamentation stains deep blue-black when the spores are mounted in solutions containing iodine and the pattern which is produced appears in many cases to be of a specific character.
The majority of the species, if not all north-temperate species are mycorrhizal and the familiar host-tree fungus relationship can be recognised:—
R. claroflava Grove, with birch in boggy places, R. emetica (Fries) S. F. Gray with pine in wet places, R. betularum Hora with birch in grassy copses and R. sardonia Fries with pines. Brief notes are here included giving the basic characters of eight common species, but it must be appreciated the identification of many species within this genus is difficult.
R. atropurpurea (Krombholz) Britz. Blackish purple russula
Cap: width 50-100 mm. Stem: width 14-25 mm; length 60-80 mm.
Cap: deep reddish purple but becoming spotted with either cream-colour or white blotches.
Stem: white but becoming flushed greyish or stained brownish with age.
Gills: white then very pale yellow.
Flesh: white in cap and stem.
Spore-print: white.