[4] The situation is further complicated by the variety of terms in use for infrageneric ranks, especially of the Old World species, that is Antirrhinum, sensu stricto (e.g. Streptosepalum, Kicksiella, Meonantha).

By contrast the narrow circumscription (sensu stricto) confines the genus to the monophyletic Old World perennial species with a diploid chromosome number of 16, distributed in the Mediterranean basin, approximately 25 species.,[8] following the phylogenetic analysis of Vargas et al. (2004) suggesting they are a distinct group.

For a comparison of earlier schemes see Mateu-Andrés and de Paco, Table 1 (2005)[10] If the broad circumscription is accepted, its three sections as described by Thompson are as follows (two Old World, one New): While Antirrhinum majus is the plant that is usually meant by the term of "snapdragon" if used on its own, many other species in the genus, and in the family Scrophulariaceae more widely, have common names that include the word "snapdragon".

[11] The following species are recognised in the genus Antirrhinum:[6] The name "Antirrhinum" is derived from the Greek ἀντίρρινον antirrhinon which in turn is derived from ἀντί anti "opposite, counterfeiting", and ῥίς rhis "nose" (GEN ῥινόϛ rhinos); from its resemblance to an animal's mouth.

They do best in full or partial sun, in well-drained soil since their roots are susceptible to rotting (although they do require regular watering[13]).

They are susceptible to ethylene gas, so removing dead flowers and keeping them away from ripe fruits or vegetables also helps them bloom longer.

[14] They grow during their peak seasons of April to June and August to October in the Northern Hemisphere[14] and bloom in a variety of colors such as white, yellow, orange, red, purple, pink,[15] including multicolored patterns.

Antirrhinum is a genus that has been used from the earliest genetic studies of Gregor Mendel and Charles Darwin and was used as a model by Erwin Baur.

Any cross between red-flowered and white-flowered snapdragons, give an intermediate and heterozygous phenotype with pink flowers, that carries both the dominant and recessive alleles.