Geranium Brittlegill

Geranium Brittlegill (Russula fellea) is the archetypal "all one colour" brittlegill. In most Russula species the cap is one colour and the stipe another, but here the cap, the gills and the stipe are all a matching pale straw, honey or buff, so the whole mushroom reads as a single soft yellow tone. That uniformity, once noticed, is nearly diagnostic on its own.

Adding to the case is the odour: fresh fruiting bodies smell strongly of crushed geranium (pelargonium) leaves, sometimes described as stewed apple or apple compote. The scent is strongest at the gills and intensifies as the mushroom dries in the collecting basket.

It is a species of beech woods, and in a mature beech hanger on chalk it is often abundant, forming scattered troops in the leaf litter through the autumn. It is a medium-sized, moderately firm brittlegill with a pale cream spore print, and it holds its shape better than the fragile red-capped members of the genus.

Cap

4–9 cm across, convex then flattening and finally slightly depressed. The colour is a uniform pale straw, honey-yellow or warm buff, often a shade deeper at the centre, and it does not develop olive, green or red tints. The surface is smooth and slightly greasy when moist, matt when dry. The margin becomes weakly grooved with age. The cuticle peels only about a quarter to a third of the way to the centre.

Gills

Pale straw to honey-cream — the same tone as the cap, which is the key character — moderately crowded, brittle, adnexed to slightly decurrent, and sometimes forked near the stipe. They discolour a little browner with age and may show faint rusty spotting.

Stipe

3–7 cm tall, 1–2 cm thick, cylindrical or slightly tapered, and again the same straw-honey colour rather than white, though it is often palest at the apex. Dry, finely wrinkled lengthwise, with no ring and no volva. Firm at first, becoming stuffed then partly hollow, and snapping cleanly.

Flesh & spore print

The flesh is whitish to pale straw and does not change colour when cut. The odour is strong and characteristic — crushed geranium leaves, or stewed apple — and is most obvious at the gills of a fresh specimen. The spore print is white to pale cream; spores are broadly ellipsoid with warts joined by fine connecting lines into a partial network.

This brittlegill is closely tied to beech, fruiting in leaf litter and on humus beneath mature trees, and it shows a strong preference for the calcareous and heavy clay soils on which beech thrives. It also occurs with hornbeam and occasionally with oak in mixed woodland where beech is present, but it is only rarely found away from beech altogether.

It is common and widespread across western, central and northern Europe wherever beech woodland occurs, including in planted beech avenues, parkland and shelterbelts. Fruiting runs from late summer through autumn, with the main flush in September and October, and the mushrooms often appear in loose troops of a dozen or more scattered across the litter.

Russula fellea is ectomycorrhizal with beech. Its mycelium wraps the tree's fine root tips in a fungal sheath and grows between the outer root cells, forming the exchange interface through which soil water, phosphorus and nitrogen pass to the tree and photosynthetic sugars pass to the fungus. Beech litter decomposes slowly and locks up nutrients, so this fungal scavenging is a significant part of the tree's nutrient budget.

The geranium-scented volatile compounds are released as the fruiting body matures and are thought to influence which invertebrates visit; in practice fungus gnats, beetle larvae and slugs all work on the fruiting bodies, hastening their collapse and recycling their nutrients into the litter layer. The mycelium itself is perennial in the soil, persisting on the beech root system between fruiting seasons and disappearing only if the host trees are removed.

Russula ochroleuca is the main confusion: it is a duller, more olive-tinged ochre, but crucially its stipe is white or grey and clearly contrasts with the cap, whereas in R. fellea the stipe matches the cap, and R. ochroleuca has no geranium odour. Russula claroflava is a much brighter chrome-yellow, grows in wet birch woods and greys strongly where cut.

Russula farinipes is a paler, more washed-out straw with a strongly grooved cap margin, a mealy bloom on the stipe and unusually elastic gills that bend instead of shattering. Russula risigallina is smaller and more delicate with a warmer orange-yellow cap and a deep ochre spore print. Uniform colour throughout, beech habitat and the geranium scent settle R. fellea quickly.