Most beginners start by learning what they want to eat. That is the wrong way round. Learn the Death Cap first, learn it so well that you recognise it at twenty paces in bad light, and everything else becomes safer.
What it looks like
A medium to large mushroom, typically with an olive-green to yellowish-green cap that often carries faint radiating fibres. Older or washed specimens fade to pale straw, and a genuinely white form occurs. Cap colour is therefore not a diagnostic feature and never should be treated as one.
The gills are pure white and stay pure white at every stage of the mushroom's life. The spore print is white. The stem carries a large drooping ring, and it often has a faint snakeskin patterning below the ring.
The feature that matters
At the base of the stem there is a bag. A sac. A cup of white tissue called a volva, from which the whole mushroom has emerged. It sits below soil level, so if you pull a mushroom out of the ground by the cap you will leave the single most important identification feature behind in the leaf litter.
Dig every specimen. Every time. It is a five-second habit that has saved lives.
Where and when
Death Caps are mycorrhizal, partnered with broadleaved trees, and in Britain they are found most often with oak and beech from late summer into autumn. They are woodland mushrooms. They do not belong in grazed pasture, which is one of several reasons why field mushroom pickers should be suspicious of anything white that turns up under trees.
Why it kills
Amatoxins destroy liver cells, and they do it slowly. Symptoms typically begin six to twelve hours after the meal - long enough for the diner to have gone to bed feeling fine. Violent vomiting and diarrhoea follow, then a deceptive period of apparent recovery lasting a day or two while liver failure progresses invisibly. Treatment is far more effective when it starts early, so any suspicion of Amanita ingestion is an emergency from the first moment, not once someone feels ill.
If you suspect a poisoning, ring 999 or go straight to A&E, and take the remaining mushrooms, or a photograph of them, with you.
The habit to build
Half a teaspoon of Death Cap is enough to kill an adult. Cooking, drying, freezing and soaking do nothing to the toxin. There is no home test, no folk rule about silver spoons or peeling caps, and no shortcut. Dig the base, look for the bag, check the gill colour, and take a spore print if there is the slightest doubt.