The ladder separates four kinds of harm. It grades the mechanism, not the severity of the afternoon: a violent but self-limiting gastrointestinal syndrome sits below a quiet compound that ends in dialysis.
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.
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.
Typical clinical burden
Irritant compounds, mostly uncharacterised; no organ damage documented.
The toxin reaches an organ and damages it. Latency is the defining hazard: Cortinarius orellanus and Amanita smithiana produce no symptoms for 3 to 20 days, by which time renal function is already falling. T2 also covers syndromes that require a co-factor, such as coprine and ethanol, or a susceptible host, such as Pleurocybella porrigens in dialysis patients.
Typical clinical burden
Organ-level injury; outcome depends on latency, dose and host.
A single meal of a normal-sized fruit body has killed, or the toxin class (amatoxins, orellanine, gyromitrin, severe muscarine load) is documented as lethal in humans. T3 does not mean every meal kills — it means the margin between a meal and a fatal dose is not wide enough to plan around, and there is no field test that measures it.
Typical clinical burden
Fatal dose reachable from one meal; no field-deployable quantitative test.