Geranium Brittlegill Identification Guide

The first impression

Beech woodland in late summer or autumn, deep leaf litter, the ground dappled and dry underfoot. You catch a small patch of warm honey-straw among the fallen leaves and, because it is almost exactly the colour of the beech mast around it, you nearly walk past. Crouch down and the important thing announces itself immediately: this mushroom is the same pale straw-yellow all over. Cap, gills and stem share one continuous washed-out honey tone, and that uniformity is the character that carries the identification.

Most brittlegills give you a contrast. A coloured cap over a white stem and white gills is the normal pattern in the genus. Geranium Brittlegill breaks that pattern, and once you have registered it, you will recognise the species from several metres away.

Reading the cap

The cap is modest for the genus, usually 4 to 9 cm across, occasionally a little more. Young caps are convex, then flatten, and mature ones become shallowly depressed at the centre so the outline looks like a low saucer.

Colour is pale ochre-straw to honey, sometimes with a faintly darker, more tawny disc and a paler margin. It is never bright, never red, never green. The surface is slightly greasy or tacky when the weather is damp and dries to a matt, faintly silky finish. The cuticle peels only a short way in from the edge, perhaps a third of the radius, which is worth testing with a fingernail because it is a genuine character rather than a party trick.

The margin is smooth and even in young specimens and develops fine, short radial grooves as the cap expands and thins. Those grooves stay shallow. If you are looking at a cap with deep, coarse, tuberculate ridging around the edge, you are almost certainly in a different part of the genus.

The gills

Turn it over. The gills are the same pale straw or very pale honey as the cap, perhaps a shade lighter, and they never go white. They are moderately crowded, fairly narrow, adnexed to almost free at the stem, and they fork here and there, mostly near the point of attachment. Some interveining develops between them in older caps.

Now do the test the common name of the whole group is built on. Run a fingertip firmly sideways across the gill faces. In brittlegills the gills shatter, snapping into fragments like the teeth of a plastic comb, because the flesh is built of spherical cells rather than filaments. Gills that bend, tear raggedly or feel rubbery belong to another genus entirely.

Stipe, base and flesh

The stem is short and cylindrical, roughly 3 to 7 cm tall and 1 to 2 cm thick, sometimes tapering slightly downwards. It is the same pale straw as the rest, usually a touch paler at the very top, with a finely wrinkled or faintly ribbed surface. There is no ring and no volva; the base simply ends, often gathering a plug of leaf litter and soil.

Snap the stem across rather than twisting it. It breaks with a clean, dry, chalky fracture, as though you had broken a stick of blackboard chalk, and the broken surface is granular rather than fibrous. Interior flesh is white to very pale straw, firm at first and softening with age; older stems become spongy or partly hollow inside.

Bruising response is minimal. Handled areas may dull to a faint brownish or more saturated honey, but there is no blackening, no reddening, no blueing, no milk. If a white latex seeps from the cut gills you are holding a milkcap, not a brittlegill.

The odour

This species is named for its smell and the name is accurate. Bruise the gills or crush a fragment of flesh between finger and thumb, warm it, and sniff. There is a sharp, sweetish, slightly fruity scent that most people read straight away as the leaves of a pelargonium, the pot geranium of windowsills, with an undertone that some describe as apple-like. It is not mushroomy and not mealy. A fresh, dry specimen on a warm afternoon gives the clearest reading; waterlogged specimens after heavy rain smell of very little.

Taking a spore print

Colour of the spore deposit matters a great deal in this genus, and small differences count, so make the print thick enough to judge. Cut the cap free, place it gills-down on white paper or, better, on a white glazed tile or a strip of glass so the deposit can be scraped into a heap, cover it to hold humidity, and leave it overnight.

The print here is pale cream, decidedly not pure white but well short of ochre or deep yellow. Scrape the deposit together with a blade into a thick ridge and judge the colour of the mass, not of the thin outer smear, and judge it in daylight rather than under artificial light.

Substrate, season and habitat

Geranium Brittlegill is ectomycorrhizal and its overwhelming preference is for beech. Find it on the litter and humus of beech woodland, both on chalk and on more neutral soils, occasionally under other broadleaf trees where beech is nearby. It grows from the ground, never from wood, though it will happily push up through a buried rotten branch.

The season is summer through autumn, with the main flush arriving with the general autumn fruiting and continuing until the first hard frosts. Fruitbodies are usually scattered or in small loose groups rather than in tight clusters or rings.

Separating the look-alikes on morphology

Russula ochroleuca is the species most often confused with it and is abundant in the same woods. Its cap is a duller, greyer ochre-yellow, but the decisive difference is that its gills and stem are white to whitish, not straw-coloured, so it shows the normal brittlegill contrast that this species lacks. It also lacks the pelargonium scent and its stem often greys with age.

Russula foetens is far larger and coarser, with a glutinous ochre-brown cap, a deeply and coarsely grooved, tuberculate margin, gills that weep droplets and spot brown, and a heavy oily-rancid smell.

Russula farinipes shares the pale straw palette but has a strongly and deeply grooved cap margin, a stem with a mealy or powdery upper surface, and unusually tough, elastic gills that resist the shatter test rather than snapping.

Russula raoultii and other pale, whitish-yellow species tend to associate with birch or other hosts, are paler and more washed-out, and again keep whitish gills.

Milkcaps of similar colour are eliminated instantly by cutting the gills and watching for latex, and by their pliable rather than brittle gills.

Putting it together

Beech overhead, straw-honey colouring running unbroken from cap to gills to stem, gills that shatter under a fingertip, a chalky-snapping stem, a shallowly grooved margin, a pale cream print and a clear pelargonium scent. Any four of those in combination is a confident identification.