A new natural ergopeptine, ergosedmine, was isolated from sclerotia of the ascomycete Claviceps purpurea. Its structure was elucidated by 1D- and 2D-NMR spectroscopy and mass spectrometry as N-(N-lysergyl)-cyclo(isoleucyl-phenylanalyl-prolyl). Partial epimerization of ergosedmine into ergosedminine was evident during purification and in DMSO-d₆. According to common ergot alkaloid nomenclature ergosedmine belongs to the ergoannines, one of the four subgroups of ergopeptines. The sclerotia were obtained from reed feather grass (Calamagrostis arundinacea). Phylogenetic analyses using ITS- and beta-tubulin sequences of pure culture isolates obtained from the C. purpurea sclerotia demonstrated that the ergosedmine-producing strain belongs to the genotype G2, which is associated with wet and shady habitats.