Heliconius cydno, the cydno longwing, is a nymphalid butterfly that ranges from Mexico to northern South America. It is typically found in the forest understory and deposits its eggs on a variety of plants of the genus Passiflora. It is a member of the Heliconiinae subfamily of Central and South America, and it is the only heliconiine that can be considered oligophagous. H. cydno is also characterized by hybridization and Müllerian mimicry. Wing coloration plays a key role in mate choice and has further implications in regards to sympatric speciation. Macrolide scent gland extracts and wing-clicking behavior further characterize this species.

Passiflora, known also as the passion flowers or passion vines, is a genus of about 550 species of flowering plants, the type genus of the family Passifloraceae.