Flowers of most Aristolochia species possess six stamens and six carpels; however, the c 40 species of subsection Pentandrae, which grow in S United States, Mexico, N Central America, Cuba, and Jamaica, have flowers with five stamens and five carpels. The sister group of this subsection consists of five hexandrous species from subtropical and temperate areas of South America, thus matching the puzzling temperate South America-Temperate North America disjunction. The synapomorphies that support such sister-group relationship and the monophyly of subsection Pentandrae are described. An important range extension of A. pentandra Jacq., which was recently found in the Island of San Andrés (Colombia), is reported, and an update of the description and typification of this species is provided.