Greenflush Fibrecap Identification Guide

The Setting

This is a summer and autumn fungus of rich broadleaf woodland soil. You typically meet it on a shaded path edge or a bank under beech, lime or oak, sometimes in mixed woodland with a few conifers present, growing from the ground among thin litter in small scattered troops. It is mycorrhizal, so it never appears on wood. The first impression is of a pale, dry, silky-fibrous mushroom with a pointed centre, which is the general look of the whole fibrecap group, and the thing that makes you stop and pick it up is a smoky blue-green wash sitting on the top of the umbo where you would expect plain ochre.

First Impression and How to Collect It

The stature is fairly solid for a fibrecap: a broadly conical cap, a straight firm stipe, and a slightly swollen base. Collect two or three fruit bodies of different ages and dig them out with a knife rather than pulling, because base shape matters. As soon as the collection is in a box the odour builds up, and this species has one of the strongest and most memorable odours in the genus, a heavy sweet smell reminiscent of over-ripe pears or honey. Record it before the collection dries out.

Cap in Detail

The cap is 3 to 8 cm across, at first conical to bell-shaped, then expanding to broadly convex or flat with a pronounced broad umbo that persists into old age. The surface is dry and matt, covered with fine radiating fibrils that run from the umbo outwards, and towards the centre these fibrils lift and break into small appressed to slightly raised scales. The ground colour is pale: cream, straw, buff or pale ochre, sometimes with a faint pinkish tone. On top of that ground sits the diagnostic feature, a distinct blue-green to verdigris flush concentrated on and around the umbo. Its intensity varies a great deal, from an unmistakable green cap centre to a mere smoky grey-green film, and it is easiest to see in fresh young material and in oblique light. The margin is often minutely split radially in expanded caps and may carry pale fibrillose veil fragments.

Gills, Edge and Attachment

The gills are adnexed to almost free, crowded, moderately broad, and ventricose in expanded caps. Young gills are pale grey to greyish-white; with maturity they take on the dull clay-brown to olive-brown of the ripening spores. The most useful detail is the edge, which stays noticeably paler than the faces and is finely fringed or flocculose under a lens, a feature shared across much of the genus and easy to check on any fresh specimen. Occasional collections show faint greenish or reddish staining on damaged gills, but strong reddening is not part of the picture here.

Stipe, Base and Flesh

The stipe is 4 to 9 cm long and 6 to 15 mm thick, more or less equal but with a swollen base that is rounded to slightly bulbous and, importantly, not sharply rimmed or marginate. It is whitish to pale cream, sometimes flushing greenish at the extreme base or, in strongly coloured collections, faintly greenish at the apex too. The surface is longitudinally silky-fibrillose along its length and finely pruinose only in the upper part, so run a lens down the stipe from apex to base and note where the frosting stops. There is no ring and no volva. Split the fruit body lengthwise. The flesh is white, sometimes with a greenish tinge in the cap centre and occasionally a pale pinkish note in the stipe cortex, and it does not redden strongly on cutting or with handling. Absence of vigorous reddening is a positive character here, because it is exactly what separates this species from its closest relative.

Odour as a Field Character

Odour deserves its own step. Crush a fragment of cap flesh between finger and thumb and smell it immediately: expect a strong, sweet, fruity aroma that most recorders describe as over-ripe pears, sometimes with a honeyed or slightly floral edge. It is persistent and often noticeable in a closed collecting box before the specimen is even unwrapped. Odour alone does not name the species, since several related fibrecaps share it, but combined with the green umbo it is close to conclusive.

Spore Print and Microscopy

Take a print by cutting the cap free and leaving it gills down on white paper under a cover for three to six hours. The deposit is dull clay-brown, sometimes described as snuff-brown, and needs to be seen as a thick heap to judge properly; scrape it together before assessing the tone. Under the microscope, the spores are smooth-walled, ellipsoid to almond-shaped, roughly 8 to 11 by 5 to 6.5 micrometres, with no bumps, lobes or angles. That smooth outline immediately separates this species from the large group of fibrecaps with nodulose, star-shaped spores. On the gills you will find thin-walled cystidia without the thick walls and crystalline caps that characterise many other members of the genus, and this combination of smooth spores and thin-walled cystidia is why modern classifications place the species in the genus Inosperma.

Substrate, Partners and Season

The fungus is ectomycorrhizal with broadleaf trees, most often beech, lime, oak and hornbeam, on neutral to base-rich soils, and it also turns up in parkland and along wooded avenues. It fruits from soil, frequently on compacted path margins, banks and disturbed ground where the litter layer is thin. The season starts early, from midsummer, and continues through autumn, with fruiting following sustained rain. Fruit bodies come in small groups rather than large rings, and it is worth searching the same few metres of path edge in successive years because the mycelium is long-lived.

Separating It From Look-alikes on Morphology Alone

The critical comparison is Inocybe haemacta, which also carries greenish tints. It is generally smaller and more strongly fibrous-scaly, its greenish colour tends to be distributed over the cap rather than concentrated on the umbo, and, decisively, its flesh and stipe redden strongly and quickly on handling and cutting, often turning the whole stipe base wine-red. If your collection stains vividly red where you gripped it, look at that species instead.

Inocybe fraudans, also known as Inocybe pyriodora, shares the sweet pear odour but has no green anywhere; its cap is plain cream to ochre, ageing with reddish-brown tints, and cut flesh reddens noticeably. Inocybe bongardii again has the fruity odour and reddening flesh without the green flush. The scaly greyer variant of this species, sometimes recognised as var. erinaceomorpha, is greyer and more coarsely scaly with weaker green tones, and is best recorded as this species unless you are working through the complex carefully.

Inocybe calamistrata is separated by the position of the green: it is concentrated in the stipe base rather than the cap, its cap is dark brown and coarsely shaggy with recurved scales, and its habitat is wet conifer woodland. Outside the genus, Stropharia aeruginosa can look green but has a slimy blue-green cap with white veil flecks, a membranous ring, purple-brown gills and a purple-brown spore print. Any green mushroom with a viscid cap and a proper ring is not a fibrecap.

A Working Sequence

Dry fibrillose umbonate cap; blue-green wash on the umbo; strong sweet pear-like odour; pale crowded gills maturing clay-brown with a fringed paler edge; whitish stipe pruinose only at the apex with a rounded, non-marginate swollen base; little or no reddening; dull clay-brown print; smooth almond-shaped spores. Run the list in that order and the identification holds up.