Tacked knightTricholoma pessundatum

The tacked knight (Tricholoma pessundatum) is not edible: it's poisonous and causes nausea, vomiting and diarrhoea. Don't eat it raw or cooked. The real trouble is that it looks very much like the brown knights people do collect, above all the poplar knight, so it tends to end up in exactly the baskets where it shouldn't be.

Can boiling make it safe? No. Swedish guides first called it edible, then "edible after boiling", and after several poisonings in the late 1930s they listed it as poisonous. No source we found says that boiling makes it safe.

How to identify it. In short: a slimy brown knight under pines, with small dark spots on the cap and no ring on the stem. The cap is 5–15 cm across, convex with an inrolled margin at first, then flat, smooth, and slimy and shiny in wet weather. It's reddish brown to yellowish brown with a paler, greyish pink margin that isn't grooved. The cap often carries small dark marks like dried drops, which is what its name means in German, Dutch, Swedish and Polish, though some caps have none, so a clean cap proves nothing. The gills are white to cream, crowded and notched at the stem, and pick up rusty brown spots with age. The stem is white with no ring and slowly browns when handled. It smells of meal, like fresh flour.

How to tell it from the poplar knight. Look at the trees. The poplar knight grows only with poplars and aspen: on riverbanks, in shelterbelts and parks, often in large rings. The tacked knight grows with pine, less often spruce or fir, on sandy soil. Both are slimy, brown with a paler margin and smell of meal, so without the tree nearby they are almost impossible to tell apart. If there's no poplar or aspen around, leave slimy brown knights alone.

How to tell it from other brown knights. The matt knight also grows under pine, but its cap is dry, matt, finely fibrous to scaly and never slimy. The scaly knight has a dry, woolly-scaly cap with a shaggy edge and grows under spruce. The booted knight (Tricholoma focale) has a woolly ring on the stem and orange-red bands below it. The giant knight lives up to its name: a cap up to 25 cm, a thick stem with a felty ring when young, and flesh that turns pinkish when cut. Several more brown knights have no card here yet. Tricholoma albobrunneum has a sharply defined white band at the top of the stem, T. ustale grows under beech and bruises brown, and T. fulvum has yellow flesh in the stem. Telling them apart reliably in the field is a job for an expert.

Where and when it grows. It forms mycorrhiza with pine, less often spruce and fir, in conifer and mixed woods on poor, sandy soil, usually in groups. Look for it from late summer to late autumn, most often in early and mid autumn. It's common in Scandinavia but counted as rare in Poland, Germany, the Netherlands and England, and it's on Britain's draft red list. In Ukraine it's known mainly from old herbarium collections in pine forests around Kyiv, and also from the Odesa, Kherson and Poltava regions, and recent confirmed finds are few.

What to do if you've eaten it. Symptoms usually start within a few hours: nausea, vomiting, stomach pain and diarrhoea, sometimes sweating and a racing heart. The upset can last a few days. Call 112 (999 in the UK), say you ate wild mushrooms, and keep any leftovers, peelings or photos. Be on your guard if the vomiting and diarrhoea begin six hours or more after the meal: that doesn't fit a knight. It's how poisoning by the death cap, or by another amatoxin mushroom that slipped into the basket, begins. Call 112 (999 in the UK) straight away, even if you start to feel better.