Sickener

Sickener (Russula emetica) is the archetypal red brittlegill and the species most people picture when the genus Russula is mentioned. Its scarlet cap set against green Sphagnum is one of the most photographed sights of the autumn conifer wood, and the fruiting bodies are notable for their fragility — the gills snap cleanly like chalk rather than tearing, a texture caused by rounded sphaerocyst cells packed through the flesh.

Russula is a very large genus in the Russulaceae, sharing with Lactarius the same brittle, non-fibrous flesh but lacking the milky latex that Lactarius exudes. Within the red-capped brittlegills, R. emetica has traditionally served as the reference point around which a cluster of closely similar species — R. betularum, R. nobilis, R. fageticola, R. silvestris — has been sorted, mainly by habitat and by how far the cap cuticle peels.

Modern treatments restrict the name Russula emetica fairly narrowly to the wet conifer and bog form, meaning many red brittlegills labelled with this name in older books belong elsewhere. It remains, however, the yardstick against which the whole red Russula complex is measured.

Cap

3–10 cm across, convex at first, then flattening and finally shallowly depressed at the centre. The surface is bright scarlet to cherry- or blood-red, smooth, and distinctly sticky or shining in wet weather, drying to a matt finish. Older or rain-washed caps fade unevenly to pinkish or almost white in patches. The margin is smooth when young and becomes faintly grooved with age. The cuticle peels away readily, typically to the centre or nearly so, revealing pinkish-tinted flesh beneath.

Gills

White and staying white or at most very pale cream, fairly broad, moderately spaced, adnexed to almost free from the stipe, with an even edge. They are markedly brittle and shatter under a fingernail. Some short gills are present near the margin, and the gill faces have a slight waxy sheen when fresh.

Stipe

4–9 cm tall, 1–2 cm thick, cylindrical or slightly club-shaped, pure white, often faintly longitudinally wrinkled, and dry. There is no ring and no volva at the base. The interior becomes chambered and finally hollow in mature specimens, and the whole stalk snaps cleanly across like a stick of chalk.

Flesh & spore print

Flesh is white throughout, reddish only in a thin layer immediately under the cap skin, and does not change colour when cut or bruised. The odour is faint and slightly fruity. The spore print is white to the palest cream; spores are broadly ellipsoid with prominent warts joined by fine connecting lines.

Russula emetica in the strict sense is a species of wet, acid ground under conifers. It is characteristically found in Sphagnum moss at the edges of bogs and in boggy hollows within spruce and pine plantations, and also in damp, mossy conifer woodland on peaty soil. The caps often push up through the moss so that only the red disc shows above the green.

It is widespread across northern and montane Europe, northern Asia and North America, following the range of its conifer partners and becoming more frequent northwards and at altitude. Fruiting runs from mid-summer through autumn, peaking after prolonged wet spells, and individual fruiting bodies are short-lived, often collapsing within a few days.

This is an ectomycorrhizal fungus. Its mycelium sheathes the fine root tips of pine and spruce, forming a mantle and an inward-growing Hartig net between root cells, through which water and mineral nutrients — especially phosphorus and nitrogen scavenged from acidic peat — pass to the tree in exchange for sugars produced by photosynthesis. In the nutrient-poor, waterlogged soils it favours, this partnership is a substantial part of how the host conifers obtain minerals at all.

The fruiting bodies are short-lived and are heavily used by invertebrates: fungus gnat and drosophilid larvae frequently riddle the stipe, and slugs graze the cap surface. Spores dispersed on air currents establish new mycelia that must locate a compatible root tip to persist, so populations are tied closely to stands of mature host trees and to the moisture regime of the site.

Russula betularum is the birch-wood counterpart: smaller, much paler, a soft pastel pink often almost white at the centre, and found on damp acid ground under birch rather than conifers. Russula nobilis (R. mairei) grows with beech, is firmer and more compact, its scarlet cap has a matt rather than glossy finish, and its cuticle peels only a third to half way. Russula fageticola is another beech associate with a darker, more purple-tinged red and a longer-grooved margin.

Russula sanguinea shares a red cap but has gills that run slightly down the stipe and a stipe strongly flushed rose-pink rather than pure white, and it grows under pine on calcareous ground. Russula rosea (R. lepida) is firmer and drier with a chalky, almost velvety cap surface and a cuticle that barely peels at all. Across the group, the reliable separators are habitat, how far the cap skin peels, stipe colouring and spore print shade.