Stinking Brittlegill

Stinking Brittlegill (Russula foetens) is the largest and most conspicuous of the ochre-brown brittlegills and is usually detected by nose before eye. Fresh fruiting bodies carry a heavy, oily, rancid odour that carries several metres on a still day and grows stronger as the mushroom ages.

It belongs to the subsection Foetentinae, a group of thick-capped brittlegills unified by dull ochre to honey colours, a strongly tuberculate-striate cap margin, a sticky cap surface and strong odours. Other members — R. subfoetens, R. laurocerasi, R. illota, R. farinipes — differ in the character of that odour and in chemical spot tests.

Size alone is a good first clue: this is a heavy mushroom that can reach dinner-plate proportions, with a stipe as thick as a thumb, and its swollen, egg-like young stage pushing up through litter looks quite unlike the flatter buttons of most brittlegills.

Cap

6–15 cm across, occasionally larger. Almost spherical when young, then convex and finally flat to broadly depressed. The colour is a dull ochre-brown, honey, dirty straw or tawny, sometimes darker in the centre. The surface is distinctly sticky to slimy in damp weather, drying shiny. The most useful feature is the margin: strongly and coarsely grooved, with the ridges broken into a row of small blunt warts (tuberculate-striate), a texture visible from a metre away. The cuticle peels only at the margin.

Gills

Whitish then dirty cream to pale ochre, moderately crowded, brittle, adnexed, and characteristically spotted and stained rusty or brownish with age. Young gills often exude small watery droplets along the edge in humid weather, which dry to brown flecks.

Stipe

5–12 cm tall and 2–4 cm thick, very stout and club-shaped or barrel-like, whitish then discolouring brown from the base upward. It is dry and firm at first, but soon becomes internally chambered and finally hollow with irregular cavities — cutting the stipe lengthwise to reveal the chambers is a good confirming step. No ring, no volva.

Flesh & spore print

The flesh is whitish, firm, browning slowly where damaged. The odour is strong, unpleasant and oily-rancid, sometimes with an almond note in the mix. The spore print is pale cream; spores are broadly ellipsoid with tall, coarse, mostly isolated warts.

Stinking Brittlegill grows on the ground in both broadleaved and coniferous woodland. It is found with oak, beech and birch, and also under pine and spruce, on soils ranging from acid sands to clays and mildly calcareous ground. It often fruits singly or in small scattered groups along woodland rides, on banks and in leaf litter under mature trees.

It is common and widespread across Europe, temperate Asia and North America. Fruiting begins in mid-summer, earlier than many brittlegills, and continues into autumn; specimens persist for several days, becoming increasingly stained, sticky and strongly scented as they decay.

The species is ectomycorrhizal and, like R. ochroleuca, is a generalist that will partner both broadleaved trees and conifers. Its hyphal mantle on the fine root tips extends the host's access to soil water and mineral nutrients, particularly phosphorus, in exchange for carbohydrates. Being unfussy about host and soil, it is one of the more widely distributed brittlegills.

The strong volatile compounds responsible for the odour make the fruiting bodies highly attractive to flies and beetles, and specimens are typically riddled with larvae by the time they flatten. This insect traffic contributes to spore dispersal alongside wind-borne release from the gills. As the soft, sticky fruiting bodies collapse into the litter they return nutrients rapidly to the soil surface.

Russula subfoetens is very similar but slightly smaller and paler, and its flesh turns bright chrome-yellow when a drop of potassium hydroxide is applied, whereas R. foetens shows little or no such reaction. Russula laurocerasi has a distinctive cherry-laurel or marzipan odour instead of the rancid oily smell, and under the microscope has spores with exceptionally tall winged ridges.

Russula illota is darker and more purple-brown with tiny dark purple flecks along the gill edges, visible with a lens. Russula farinipes is smaller and paler straw-yellow, with an elastic, rubbery gill texture that resists shattering and a stipe with a mealy bloom. Size, cap sliminess, the grooved warty margin, gill spotting and odour type separate the group in the field.