KingdomFungiGenusHypholomaSpeciesfasciculare
Hypholoma fasciculare
T1 · Gastrointestinal irritantPublished 2026-10-04Spring / Summer / Autumn / Winter
Sulphur tuft is one of the most reliably identified wood-rotting agarics in the temperate zone and one of the most frequently eaten by mistake, because its colour scheme is attractive and its habit — dense tufts on a stump — is exactly where people expect to find edible mushrooms. It is bitter enough that most people stop after one mouthful, which is the only reason it is not a more serious public health problem.
Block 01 · Record
The gill colour sequence
The gills start sulphur-yellow, pass through olive-green, and end dark purple-brown as the spores mature, and the change runs from the stem outward so that a single specimen often shows all three colours at once. No other common wood-rotting tuft-forming agaric does this. Hypholoma capnoides, which grows on conifer wood in the same forests, has gills that are smoky grey from the start and never green. Armillaria mellea has a white spore print and never shows the green phase at all.
Spores, the germ pore and the guaiac test
The spore print is dark purple-brown with a distinctly purplish cast in a thin deposit — a colour no other common tuft-forming wood agaric in these forests shares. Spores are 6-8 x 4-4.5 micrometres, ellipsoid with a truncated apex and a small germ pore, smooth, thick-walled and inamyloid. On the bench, guaiac tincture turns fresh context blue within thirty seconds, a strong positive that identifies the species as a white-rot wood decayer with extracellular laccase.
All-year fruiting and the substrate
The species is unusual in this collection for fruiting in every month of the year: the main flush runs from September to November, but fresh tufts appear in mild spells in January and February and again in late spring. It grows on the dead wood of both conifers and broadleaves, including stumps, sawn logs, fence posts, buried roots and worked timber in contact with soil, and it produces black rhizomorphs that spread through the wood well beyond the visible fruit bodies. The bright yellow mycelial mat at the base of each tuft is a reliable field character.
Toxicology and the bitterness
The species contains fasciculol derivatives and a gastrointestinal irritant, and it is intensely bitter — most accounts of accidental consumption describe the meal being abandoned after the first mouthful. Symptoms, when they occur, are vomiting, diarrhoea and abdominal cramps beginning thirty minutes to three hours after the meal. It is listed at T1 because no organ damage has been documented, and the bitterness is the practical protection: a mushroom this bitter cannot be eaten in quantity without the taster noticing.
Points to carry to the bench
- Gills pass from sulphur-yellow through olive-green to purple-brown, changing from the stem outward.
- Dark purple-brown spore print with a purplish cast; spores 6-8 micrometres with a germ pore.
- Dense caespitose tufts on dead wood, with a bright yellow mycelial mat and black rhizomorphs at the base.
- Intensely bitter; T1 gastrointestinal irritant with no documented organ damage.
| Cap | shape: Convex to plano-convex, 20-60 mm across, often irregular where fruit bodies crowd each other; the margin is incurved when young.surface: Smooth and matte, sulphur-yellow to greenish-yellow, with an orange-brown to reddish-brown disc that occupies the central third.margin: Even and entire; a few white fibrils of the veil may adhere in very young specimens but never form a ring. |
|---|---|
| Gills | attachment: Adnate to narrowly adnexed, close against the stem with no gap and no decurrent run.spacing: Crowded, 3-5 gills per millimetre, with two or three series of intermediates.edge: Entire, yellow when young, becoming olive-green then dark purple-brown as the spores mature — the colour sequence runs from the stem outward. |
| Spore print | Ellipsoid to oval in profile, with a truncated apex and a small germ pore.Smooth, thick-walled, inamyloid; a few spores show a faint suprahilar depression. |
| Habitat and season | Saprotrophic on dead wood of both conifers and broadleaves — stumps, logs, fence posts, buried roots and worked timber — and, less often, on soil over buried wood. Fruits in dense caespitose tufts and, unlike most agarics in this collection, is found in every month of the year. |
Block 02 · Chemistry
| Reagent | Verdict | Reaction | Weight |
|---|---|---|---|
 MELZ | inamyloid | Spore wall stays yellow-brown and the germ pore does not darken; no blue-black development. | 3.00 |
 KOH5 | negative | Cap surface darkens to olive-brown; the yellow and green pigments are stable to alkali. | 2.00 |
 FESO4 | negative | Flesh unchanged after 60 s. | 3.00 |
 GUAIAC | positive | Fresh context turns blue within 30 s — a strong positive, consistent with a white-rot wood decayer rather than a litter saprotroph. | 1.00 |
Injury stain None. The cap, gills and stem keep their colours when cut, and the yellow mycelial mat at the base does not brown or blacken. Bruising produces no reaction at any stage.
Block 03 · Confusion
| Separating character | This record | Confused with |
|---|---|---|
| Gills that are smoky grey to grey-brown from the start and never pass through a green phase, a paler honey-yellow cap without the orange disc, and growth almost exclusively on conifer wood. | Hypholoma fasciculareT1 | Hypholoma capnoides▲ +1 |
| A rusty-brown rather than purple-brown spore deposit, ornamented amygdaliform spores with a plage, and a membranous ring on the upper stem; the spore print colour is the fastest separation. | Hypholoma fasciculareT1 | Galerina marginata▲ +2 |
| A white spore print, a persistent cottony ring on the upper stem, and a honey-brown cap with dark scales at the centre; it also produces black rhizomorphs under the bark. | Hypholoma fasciculareT1 | Armillaria mellea▲ +1 |
Toxicity ladder
Reproducible vomiting, cramping and diarrhoea with no hepatic, renal or neurological involvement. Onset is short and recovery is complete, but the same species can produce a severe dehydrating episode in children and in people on diuretics or beta blockers.
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