Golden Brittlegill Identification Guide

First impressions

Golden Brittlegill is a small, neat, warmly coloured mushroom of broadleaved woodland. You typically find it in ones and twos on the leaf-littered floor under oak, beech or birch, often near a path edge or in a grassy woodland clearing, from midsummer through autumn.

The difficulty is that it does not look the same twice. This species is a notorious chameleon: one cap may be soft apricot, the next lemon-yellow, the next salmon-pink or rosy with a yellow centre, and some carry olive or greenish flushes. Colour is close to useless as a starting point. What you use instead is the combination of small size, deep egg-yellow gills, a chalk-white brittle stem and an unusually strongly coloured spore print.

Before anything else, confirm the genus. Flick the edge of a gill with a fingernail: in a brittlegill the gills shatter and crumble rather than bending. Snap the stem across: it breaks cleanly and abruptly, like a stick of blackboard chalk, with no fibrous strings. Break a piece of cap flesh: it is granular and crumbly, not fibrous. Finally check that no milky fluid appears on any broken surface - if it does, you are in Lactarius, not Russula.

Reading the cap

The cap is small for the genus, typically 3-6 cm, occasionally a little more. It is convex at first, then flattens and finally becomes slightly depressed in the centre. The surface is matt to faintly shining, dry in fair weather and slightly greasy when wet.

Two structural details matter more than colour. First, the cuticle peels: with a fingernail you can strip the coloured skin back from the margin for roughly half to nearly all of the radius, which places it among the thinner-skinned Russulas. Second, the margin becomes distinctly striate with age - fine radial grooves, often lumpy or tuberculate, appear around the rim of a mature cap. Both features are consistent even when the colour is not.

Record the colours you actually see rather than trying to match a name. Note whether the centre is darker or paler than the rim, whether there is any pink over yellow, and whether the colour has washed out with rain.

The gills - the colour to trust

Turn the cap over. Young gills are pale cream, but they ripen to a deep, saturated egg-yellow or ochre-yellow that is much stronger than the pale cream or ivory gills of most brittlegills. This deep yellow is the character to anchor on, and it should be assessed on a fully mature cap in daylight, not on a young button and not under woodland shade.

The gills are adnexed to nearly free, moderately spaced rather than crowded, brittle, and mostly of equal length, with relatively few short intermediate gills and little forking. The edges are even and concolorous. Because the gills are so deeply coloured, spore deposit and gill colour reinforce each other in this species, which is convenient in the field.

Stipe, base and flesh

The stem is white, cylindrical or slightly club-shaped, 3-6 cm long and around 1 cm thick, without any ring or veil. It is chalky and brittle - the classic Russula snap - and becomes spongy or chambered inside as it ages. Older stems may develop faint grey or brownish tones near the base, but the stem never has the pronounced blackening seen in some other groups.

The base is simply rounded or slightly tapered, with no bulb, sac or volva, and it lifts cleanly from litter. Excavate it, because the presence or absence of a bulb is worth checking on any unfamiliar agaric.

The flesh is white, thin and fragile, and it stays essentially white on cutting, at most greying very faintly with time. There is no reddening, no strong blackening and no latex. Smell is faint but characteristic when several fruitbodies are collected together - fruity, often described as apricot or stewed fruit. Iron salts applied to the stem flesh give only a weak pinkish or almost no reaction, which is a supporting rather than a decisive test.

The spore print - do this carefully

For brittlegills the spore print colour is not a yes-or-no check but a graded measurement, and this species sits at the strongly coloured end of the scale.

Use two or three mature caps. Remove the stems, place the caps gills-down on white paper or, better, on a white glass tile or microscope slide, cover with a bowl and leave overnight in a cool, still, humid place. Six to twelve hours gives a usable deposit; longer gives a better one.

Then the crucial step: scrape the deposit into a thick, dense heap with a razor blade or knife edge before judging it. A thin dusting of even the most strongly coloured Russula spores looks pale and washed out. Assess the heap in daylight against a white background. For Golden Brittlegill you should be looking at a deep ochre to egg-yellow - one of the darkest yellows found in the genus, well beyond cream or pale buff.

Under a microscope the spores are subglobose to broadly elliptical, roughly 6-9 x 5-7 micrometres, and ornamented with warts and short ridges that are largely isolated rather than forming a full network.

Substrate and season

Golden Brittlegill is ectomycorrhizal, growing in partnership with tree roots and fruiting from soil. Oak, beech and birch are its usual partners, with records under lime, hornbeam and hazel; it occurs on a range of soils and often shows up in grassy or mossy woodland margins and parkland with scattered old trees. Fruiting runs from midsummer to mid autumn. It never grows on wood, and it does not appear in pure conifer stands.

Separating the look-alikes

All the close relatives are small, yellow-spored, mild-fleshed brittlegills, so work through structure and print grade rather than cap colour.

• Russula lutea is the nearest. Its cap is more consistently and evenly egg-yellow to apricot, without the pink, salmon and olive variants, and it tends to be a little smaller and even more fragile. Its print is deep yellow too, so separation rests on cap colour range and on spore ornamentation under a microscope, where lutea shows a partially connected pattern.
• Russula odorata is an oak associate with a duller ochre to brownish-violet cap, a strong fruity odour and a paler ochre print.
• Russula nauseosa has grey-violet to purplish-brown tones, a strongly striate margin, and grows with conifers, especially spruce and pine.
• Russula puellaris is small with purplish-brown to date colours and, decisively, yellows strongly all over as it ages, particularly the stem.
• Russula velenovskyi has a red to brick cap, often greenish at the centre, a stouter stem and a cream to pale ochre print, clearly paler than this species.
• Russula ochroleuca is much larger, dull ochre-yellow, thicker fleshed, and drops a pale cream print.

Field checklist

Small brittle-gilled mushroom under broadleaves; variable apricot, yellow, pink or salmon cap; cuticle peeling well; striate margin when mature; deep egg-yellow mature gills; white chalky snapping stem; white unchanging flesh; faint fruity odour; and a densely scraped spore print of deep ochre-yellow. The print grade is the anchor - if it comes up cream, look elsewhere in the genus.