Green Skinhead Identification Guide

Where You Meet It

This is an autumn woodland fungus of the soil, not of wood. You typically find it from late summer to late autumn, growing among leaf or needle litter in broadleaf woodland with beech and oak, and in montane conifer forest where a variety with a slightly different aspect occurs. It is mycorrhizal, so it appears where roots are, often in loose troops of a few to a dozen fruit bodies spread over a couple of square metres, frequently on banks, path edges and mossy ground. The colour is what stops you: a matt olive-green cap sitting in brown litter reads as distinctly odd, because most green woodland agarics are either slimy or waxy and this one is neither.

First Impression

A medium-small, dry, dull-surfaced mushroom with an olive to olive-brown cap, olive-yellow flesh tones running through the stipe, and gills that look green in youth and rusty in age. The stature is fairly stocky for its size, the cap rarely much broader than the stipe is long, and the whole fruit body has a slightly fibrous, felted quality rather than a smooth or greasy one. Collect several ages if you can; the transition from green to rust across the gills is one of the most informative characters and is only visible when you have young and old material side by side.

Cap in Detail

The cap measures roughly 2 to 6 cm, occasionally 8 cm, convex at first and expanding to broadly convex or almost flat, usually with a low broad umbo. The surface is completely dry to the touch, matt, and covered with fine radial fibrils that break up into minute appressed scales, particularly towards the centre. It never has a slimy or tacky skin, which excludes an entire section of the genus at a stroke. Colour ranges from dark olive-green through olive-brown, generally darkest at the centre and yellower or more olive towards the margin. The margin itself is incurved when young, thin, and sometimes carries pale fibrillose remnants of the veil.

Gills, Cortina and the Rusty Change

The gills are the character to concentrate on. In young fruit bodies they are a striking olive-green to olive-yellow, adnate to slightly notched at the stipe, crowded, with intermediate gills of shorter length between the full ones. As the spores mature, rust-brown spore dust accumulates and clouds the green, so mid-aged specimens look olive with a rusty film and old ones are essentially cinnamon-rust with only traces of olive at the gill edge. The edges tend to stay paler and slightly uneven. Between the cap margin and the stipe, young fruit bodies carry a cortina, a fine cobweb of pale olive-yellow fibres. It collapses early, leaving irregular fibrillose girdles on the upper stipe that catch falling spores and turn rusty; that rusty ring zone on a fibrillose stipe is a reliable genus marker.

Stipe, Base and Flesh

The stipe is 3 to 8 cm long and 4 to 10 mm thick, more or less cylindrical, sometimes slightly thickened downwards but never with an abrupt marginate bulb. It is olive-yellow overall, silky to finely fibrillose, often with darker olive fibrils that form indistinct bands and with rust-coloured dusting in the upper half. Dig it out rather than pulling it; the base usually carries olive-yellow to yellowish mycelial threads binding litter, and there is no sac, no volva and no membranous ring. Split the fruit body from cap to base with a knife. The flesh is thin, firm and pale olive-yellow to yellowish, most strongly coloured in the stipe cortex and base, and it does not change dramatically on exposure to air; expect at most a slight darkening. Odour is faint and earthy, occasionally with a hint of raw root vegetable, and is a supporting note rather than a decisive one.

Spore Print and Spores

A spore print is essential for this species because it converts a guess into a genus. Cut the cap free, place it gills down on white paper, cover with a bowl to keep humidity up, and leave it for three to six hours or overnight. The deposit is rust-brown to cinnamon, and it is worth seeing on white paper rather than dark, since the exact warmth of the brown is diagnostic. Under a microscope the spores are ellipsoid to broadly ellipsoid, about 6 to 8.5 by 4 to 5.5 micrometres, with a distinctly warted, roughened surface and a dextrinoid reaction. Rusty print plus warted spores plus a cortina is the core of the genus.

Habitat, Partners and Season

The fungus is ectomycorrhizal with trees, so record the trees within about ten metres of the collection. In lowland woodland the usual partners are beech and oak, sometimes with birch or hornbeam nearby, on moderately acid soils. In upland and montane forest it occurs with spruce and other conifers, and material from those habitats is often recognised as a distinct variety on subtle differences in colour and stature. Fruiting runs from late summer through the main autumn season, peaking after sustained rain and dropping away with the first hard frosts. It fruits on soil among litter and moss, never on rotten wood.

Separating It From Look-alikes on Morphology Alone

Cortinarius cotoneus is the closest relative in the field. It is markedly larger and more robust, with a cap commonly 5 to 10 cm, more olive-brown than green, and a distinctly felted to finely scaly surface; its gills are olive-brown rather than the clean olive-green of young Green Skinhead, and its spores are larger and more rounded with coarser warts. Cortinarius atrovirens looks green but belongs to a different group: its cap is glutinous rather than dry, its stipe ends in a bulb with a distinct rim, and the whole fruit body is chunkier.

Outside the genus, Stropharia aeruginosa has a slimy blue-green cap flecked with white veil scales, a proper membranous ring on the stipe, gills that mature purple-brown rather than rust, and a purple-brown spore print; it also favours grassy ground and litter rather than mycorrhizal woodland positions. Hygrocybe psittacina is glutinous all over, with thick, waxy, widely spaced gills and a white spore print. Green-tinted Tricholoma species have white spore prints, deeply notched gills, no cortina and no rusty dusting, and their flesh is white rather than olive. Finally, within the same subgroup of Cortinarius, the cinnamon and blood-red species share the fibrillose dry cap and rusty print but have no olive-green tones anywhere; comparing the colour of the young gills against the colour of the split stipe flesh usually resolves them at a glance.

A Working Sequence

Confirm soil habitat under known partner trees; confirm a dry fibrillose cap; look for the cortina or its rusty remnant girdles; note olive-green young gills clouding to rust; split the fruit body to confirm olive-yellow flesh; then take a rusty spore print. That chain, in that order, is what turns an odd green mushroom into a confident record.