Antirrhinum is a genus of plants that used to be the family Scrophulariaceae, more commonly known as snapdragons from the flowers' fancied resemblance to the face of a dragon that opens and closes its mouth when properly squeezed (thus the 'snap'). Study of DNA sequences have led to the inclusion of Antirrhinum in a vastly enlarged family Plantaginaceae.
The taxonomy of this genus is disputed at present. At one extreme, ITIS recognises only the Old World species of sect. Antirrhinum in the genus, listing only the Garden Snapdragon A. majus (the only species in the section naturalised in North America). At the other, Thompson (1988) treated 36 species in the genus; many modern botanists accept this circumscription. New species also continue to be discovered (see e.g. Romo et al., 1995).
Recent research in the molecular systematics of this group, and related species, by Oyama and Baum (2004), has confirmed that the genus as described by Thompson is monophyletic, provided that one species (A. cyathiferum) is removed to a separate genus, and two others (previously listed as Mohavea confertiflora and M. breviflora) are included. It is widely agreed that this broad group should be subdivided into three or four subgroups, but the level at which this should be done, and exactly which species should be grouped together, remain unclear. Some authors continue to follow Thompson in using a large genus Antirrhinum, which is then divided into several sections; others treat Thompson's genus as a tribe or subtribe, and divide it into several genera.