Antirrhinum is a genus of plants commonly known as dragon flowers or snapdragons because of the flowers’ fancied resemblance to the face of a dragon that opens and closes its mouth when laterally squeezed. They are native to rocky areas of Europe, the United States, and North Africa.[1]
The taxonomy of this genus is complex and not yet fully resolved at present. In particular the exact circumscription of the genus, especially the inclusion of the New World species (Saerorhinum), is contentious.[2] 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).
The USDA Plants Database recognises only two species: A. majus (the garden snapdragon), the only species naturalised in North America, and A. bellidifolium (the lilac snapdragon), now considered to be Anarrhinum bellidifolium (L.) Willd.[3] As of April 2017, The Plant List (Version 1.1) accepts 21 species.[4]
A widely accepted scheme (Thompson 1988) placed 36 species in the genus in three sections. While many botanists accepted this broad circumscription (sensu lato), whose main departure from other classifications was the inclusion of the New World Saerorhinum,[5] others did not, restricting the genus to the Old World. (For a comparison of Thompson with earlier systems, see Oyama and Baum, Table 1.) New species also continue to be discovered (see e.g. Romo et al., 1995).
In 2004 research into the molecular systematics of this group and related species by Oyama and Baum confirmed that the genus sensu lato as described by Thompson is monophyletic, provided that one species (A. cyathiferum) is removed to the separate genus Pseudorontium, and the two species of Mohavea (Mohavea confertiflora and M. breviflora) are included. The species list given here follows these conclusions.[2]
This is the broad circumscription that includes the Old World Misopates and New World Sairocarpus. 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. (Tolety 2011), following the phylogenetic analysis of Vargas et al. (2004) suggesting they are a distinct group. Both Misopates and Sairocarpus are accepted names in The Plant List, and many of the New World species now have Sairocarpus as their accepted name, rather than Antirrhinum. It has been proposed that many of the New World Antirrhinum be now considered under Sairocarpus, in the forthcoming Flora of North America.[6]
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