The genus Arctopus L. is revised. It is an anomalous member of the family Apiaceae, with several unusual morphological characters such as the prostrate spiny leaves, thick resinous tuberous roots, sessile female flowers with a homochlamydeous perianth, and pseudanthia formed by distinctive bracteoles. The three species of Arctopus were found to differ mainly in their reproductive morphologies, being easily distinguishable by the large involucral bracteoles that surround the female pseudanthia. The anatomy of the petiole as well as the morphology of the inflexed spines and leaf margins were also found to be useful diagnostic characters and are illustrated and discussed. Possible phylogenetic relationships were explored using both morphological and DNA sequence data (ITS). A formal taxonomic treatment is presented, including a key to the species, correct nomenclature, typification, descriptions, illustrations, and distribution maps.