Claviceps is a genus of fungi known for its parasitic relationship with grasses, particularly rye. These fungi infect the seeds of the host plants, replacing them with dark, elongated structures called sclerotia. These sclerotia can contain alkaloids, which are compounds that can be toxic to humans and animals. The most well-known species within this genus is Claviceps purpurea, which produces ergot, a substance that has been historically linked to various health issues, including ergotism. This condition can cause severe symptoms such as hallucinations and gangrene when contaminated grains are consumed.