An ergot kernel called Sclerotium clavus develops when a floret of flowering grass or cereal is infected by an ascospore of C. purpurea.

The proliferating fungal mycelium then destroys the plant ovary and connects with the vascular bundle originally intended for feeding the developing seed.

When a mature Sclerotium drops to the ground, the fungus remains dormant until proper conditions trigger its fruiting phase (onset of spring, rain period, need of fresh temperatures during winter, etc.).

In the head, threadlike sexual spores (ascospores) are formed in perithecia, which are ejected simultaneously, when suitable grass hosts are flowering.

The size of conidia can be an indication but it is weak and it is necessary to pay attention to that, due to osmotic pressure, it varies significantly if the spores are observed in honeydew or in water.

Spartina, Distichlis (G3) Setaria Claviceps purpurea has been known to humankind for a long time, and its appearance has been linked to extremely cold winters that were followed by rainy springs.

Monks of the order of St. Anthony the Great specialized in treating ergotism victims[16] with balms containing tranquilizing and circulation-stimulating plant extracts; they were also skilled in amputations.

[citation needed] The common name for ergotism is "St. Anthony's Fire",[16] in reference to monks who cared for victims as well as symptoms, such as severe burning sensations in the limbs.

During the Middle Ages, human poisoning due to the consumption of rye bread made from ergot-infected grain was common in Europe.

Gordon Wasson proposed that the psychedelic effects were the explanation behind the festival of Demeter at the Eleusinian Mysteries, where the initiates drank kykeon.

[21] Linnda R. Caporael posited in 1976 that the hysterical symptoms of young women that had spurred the Salem witch trials had been the result of consuming ergot-tainted rye.

[citation needed] British author John Grigsby claims that the presence of ergot in the stomachs of some of the so-called 'bog-bodies' (Iron Age human remains from peat bogs N E Europe such as Tollund Man), reveals that ergot was once a ritual drink in a prehistoric fertility cult akin to the Eleusinian Mysteries cult of ancient Greece.

[citation needed] An outbreak of violent hallucinations among hundreds of residents of Pont St. Esprit in 1951 in the south of France has also been attributed to ergotism.