White knightTricholoma album

The white knight (Tricholoma album) is not edible and is poisonous, so it's not worth picking. Its flesh is acrid and bitter, its smell is strong, and British references list it among the fungi that irritate the stomach and gut. The bigger risk with white knights, though, is confusing white gilled mushrooms with the deadly white amanitas.

Can you cook it? No. Soaking and long boiling remove neither the bitterness nor the smell, and they don't prevent the stomach upset. None of the field guides we checked calls it edible. If you find a white knight with a sharp smell, leave it in the wood.

How to identify it. The cap is 4–10 cm across, white to cream, dry and matt, never slimy. Young caps are convex with an inrolled margin, then flatten out around a small low boss, and the centre turns ochre with age. The gills are white, thick, fairly distant and notched just before the stem. The stem is white and cylindrical, with no ring and no volva, and slowly browns when handled. The most telling feature is the smell: sharp like radish, with a sickly sweet note of honey. You can often smell a group before you see it.

Where and when it grows. It's mycorrhizal, mainly with oak, less often with beech, hornbeam, hazel and birch, in broadleaf and mixed woodland on sandy or loamy soil, along woodland edges and in parks. It often grows in troops and fairy rings. It occurs across Europe, from Scandinavia to the Mediterranean, and in Ukraine. Look for it from late summer through autumn, most of all in early and mid autumn.

The white knight has a near twin, the chemical knight (Tricholoma stiparophyllum). It grows with birch, is larger, often has a ribbed cap margin and a nauseating, chemical smell like cooked beetroot. Some mycologists treat the two as one species, and many older records of white knight are really the birch twin. For a forager it makes no difference: neither is edible.

How to tell it from the death cap and the destroying angel. White forms of the death cap and the all white destroying angel are deadly. They have a ring or skirt on the stem (which can fall off) and a bag-like volva around a swollen base that often stays in the ground, and their gills are free of the stem. So never cut a white mushroom at ground level: dig the whole thing up and look at the base. If vomiting and diarrhoea start six hours or more after a meal of white mushrooms, suspect death cap poisoning and call 112 (999 in the UK) straight away, even if you start to feel better.

Other look-alikes. St George's mushroom is also white, but it fruits in spring, smells of fresh flour and has very crowded, narrow gills. The blue spot knight (Tricholoma columbetta), an edible white knight without its own card here, is almost odourless, has a silky cap and often blue-green spots on the stem. The horse mushroom has pink, then chocolate-brown gills, a ring and an aniseed smell. The ivory funnel and the fool's funnel are small, thin, grow in grass and have gills running down the stem. The ivory woodwax is slimy with waxy gills, and the soapy knight smells of soap.

If you've eaten a white knight and feel sick, vomit, or have stomach pain or diarrhoea, call 112 (999 in the UK) and say you ate wild mushrooms. Keep any leftovers, peelings or photos: they help doctors rule out something more dangerous.