KingdomFungiGenusBoletusSpeciesedulis
Boletus edulis
T0 · No known toxinsPublished 2026-08-16Summer / Autumn
The cep is the reference bolete, and the reason it is easy to be confident about is structural rather than visual: pore surface rather than gills, a reticulate stem, and no colour change anywhere on the cut surface. Those three characters together exclude every T1, T2 and T3 bolete in temperate Europe, and none of them depends on the cap colour, which varies from almost black to tan.
Block 01 · Record
The three characters that do the work
First, the pore surface: white to cream when young, yellowing to olive at maturity, never red or orange. Second, the stem reticulum: a fine white mesh, at minimum over the upper third, standing proud of a pale ground. Third, and most useful, the cut test. Slice the cap and the stem lengthwise where you stand, wait sixty seconds, and look. Boletus edulis does not blue, does not redden and does not blacken. Every dangerous bolete in the temperate zone shows at least one of those three reactions within that minute.
Microscopy and the reagent bench
Spores are 12-17 x 4-6 micrometres, subfusiform with a suprahilar depression, smooth, inamyloid, olive-brown in deposit. A spore print needs a night on white paper and reads as a dull walnut stain that is easy to mistake for a dirty smudge. On the bench, iron(II) sulfate on the flesh gives a grey-green wash over 60-90 seconds — a slow, dull reaction. A fast salmon-pink reaction to iron salts indicates a russula or a Tricholoma, not a bolete.
Habitat and season
The species is a generalist mycorrhizal partner and fruits with spruce, pine, oak, beech and birch, which is why it turns up in almost every mature woodland type on acidic, free-draining soil. Stands younger than about thirty years rarely produce. Fruit bodies are strongly gregarious — if you find one, mark the spot, because the same mycelium will fruit there for decades. The season runs from late June in a wet year through November, with the main flush in September and early October after a cool, wet fortnight.
Discrimination and the bitter bolete
Rubroboletus satanas is the pair that matters: its pore surface is blood-red from the very earliest stage, its cap is pallid grey-white, and its flesh blues within ten seconds of cutting. Tylopilus felleus is not toxic but is so bitter that a single fragment ruins a meal; it ages to a pink pore surface and carries a coarse dark reticulum. Neither of those two requires microscopy, and both are resolved by the cut test before the specimen reaches the basket.
Points to carry to the bench
- Pore surface white to olive, never red or orange at any age.
- Fine white reticulum on the stem, at least over the upper third.
- Cut test: no blueing, no reddening, no blackening within 60 seconds.
- A pink-flushing pore surface or a dark coarse reticulum means Tylopilus felleus — bitter, not toxic.
| Cap | shape: Hemispherical then convex to plano-convex, 60-200 mm across, sometimes exceeding 250 mm; margin usually entire with a thin sterile band.surface: Dry to slightly viscid when wet, finely tomentose then smooth, chestnut brown to dark brown, occasionally pale tan at the margin.margin: Inrolled at first, decurved then straight; a 1-2 mm sterile white band is usually visible where the tubes do not reach the edge. |
|---|---|
| Gills | attachment: Tubes rather than gills: 10-20 mm deep, adnate to depressed around the stem apex, so the hymenophore is notched where it meets the stem.spacing: Pores 0.3-1.0 mm across, round when young and becoming angular as the tubes expand; 2-4 pores per millimetre at maturity.edge: Pore edges thin and entire; the pore surface in this species never reddens, which is the first thing to check. |
| Spore print | Subfusiform to ellipsoid in profile, with a suprahilar depression that gives the spore a slightly waisted look.Smooth and inamyloid; wall thickness about 0.5 micrometre, with a short hilar appendix. |
| Habitat and season | Ectomycorrhizal, with a host range wide enough to include spruce, pine, oak, beech and birch; most productive on acidic, well-drained sandy loam in stands 30 years and older. Fruit bodies are strongly gregarious and re-appear at the same spots for decades. |
Block 02 · Chemistry
| Reagent | Verdict | Reaction | Weight |
|---|---|---|---|
 MELZ | inamyloid | Spore wall remains olive-yellow; no blue or red-brown development. | 3.00 |
 KOH5 | variable | Cap cuticle turns orange-brown to red-brown within 30 s on most collections; the flesh stays unchanged, which is the reading that matters. | 2.00 |
 FESO4 | slow-positive | Flesh develops a grey-green to olive wash over 60-90 s; a fast salmon-pink here indicates a different genus entirely. | 3.00 |
 NH4OH | negative | Cap cuticle darkens slightly or shows no reaction; no yellow or green flash. | 2.00 |
Injury stain None anywhere. Cap flesh, stem flesh and pore surface all keep their colour for at least an hour after cutting. This is the single fastest field check: a bolete that blues, reddens or blackens where cut is a different species and belongs to a different tier.
Block 03 · Confusion
| Separating character | This record | Confused with |
|---|---|---|
| Pore surface blood-red from the earliest stage and flesh that blues within 10 s of cutting; the cap is a pallid grey-white rather than brown. | Boletus edulisT0 | Rubroboletus satanas▲ +1 |
| Not toxic but intensely bitter: the pore surface ages to pink and the stem reticulum is a coarse dark mesh rather than a fine white one. A 5 mm fragment on the tongue is unmistakable within 15 s. | Boletus edulisT0 | Tylopilus felleus▲ +0 |
| Closely related and equally T0, separated by a strongly reticulate stem over its whole length and a paler, drier cap; the distinction is taxonomic, not one of risk. | Boletus edulisT0 | Boletus reticulatus▲ +0 |
Toxicity ladder
No toxin has been isolated or reproduced in feeding trials, and decades of documented ingestion carry no reproducible syndrome. T0 is a statement about the chemistry of the species, never a statement about a specimen in your hand.
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