Aristolochia

Aristolochia is a large plant genus with over 500 species of shrubs and herbs, many having medicinal properties. Collectively known as birthworts, pipevines or Dutchman's pipes, they are the namesake of the family (Aristolochiaceae). They are widespread and occur in the most diverse climates. Some species, like "A. utriformis" and "A. westlandii", are threatened with extinction.
"Isotrema" is usually included here, but might be a valid genus. If so, it contains those species with a three-lobed calyx.