Final answer:
The toxin associated with St. Anthony's Fire (ergotism) is produced by the fungus Claviceps purpurea, which contaminates grains such as rye and can lead to severe health problems.
Step-by-step explanation:
The organism that produces the toxin associated with St. Anthony's Fire (ergotism) is Claviceps purpurea. Ergotism is a disease that can occur when grains such as rye are contaminated with this fungus. Claviceps purpurea produces a mycotoxin called ergot toxin, an alkaloid that can lead to two forms of ergotism: gangrenous and convulsive. Gangrenous ergotism is characterized by vasoconstriction and potential gangrene in extremities, while convulsive ergotism affects the central nervous system, causing symptoms like mania and hallucinations. The other organisms listed: Aspergillus nidulans, Amanita phalloides, and Stachybotrys chartarum are not associated with the production of ergot toxin.