Antirrhinum is a genus of plants commonly known as dragon flowers or snapdragons, from 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.
Antirrhinum used to be treated within the family Scrophulariaceae, but studies of DNA sequences have led to its inclusion in a vastly enlarged family Plantaginaceae. The taxonomy of this genus is not yet fully resolved at present.
The USDA Plants Database recognises only two species. A. majus (the garden snapdragon), the only species naturalised in North America, and Antirrhinum bellidifolium (the lilac snapdragon)  As of 2014 The Plant List accepts 21 species.
A widely accepted scheme, Thompson (1988), places 36 species in the genus in three sections. Many modern botanists accept this circumscription. 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 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. The species list given here follows these conclusions.
This is the broad circumscription (sensu lato) 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. (Tolety 2011)
Both Misopates and Sairocarpus are accepted names in The Plant List.
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.
If the broad circumscription is accepted, its three sections as described by Thompson are as follows:
- Section Antirrhinum: 20 Old World species of relatively large flowered perennial plants, including the type species Antirrhinum majus, mostly native to the western Mediterranean region with a focus on the Iberian Peninsula.
- Section Orontium: two species, also from the Mediterranean. The species in this section, including the section type species Antirrhinum orontium (lesser Snapdragon) are often treated in the genus Misopates.
- Section Saerorhinum: 15 small flowered New World species, mostly annual plants and mostly native to California, though species are found from Oregon to Baja California Sur and as far east as Utah. Like other authors, Thompson placed A. cyathiferum in this section, but Oyama and Baum, following earlier authors, suggest that it should be reclassified in genus Pseudorontium, while Mohavea confertiflora and M. breviflora and Galvezia glabrata, Galvezia juncea,Galvezia rupicola and Galvezia speciosa should be included. Some authors classify the species in this section into the genera Sairocarpus, Howelliella and Neogaerrhinum.
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".
The word "antirrhinum" is derived from αντίρῥῑνόν "antirrhinon" which in turn was derived from Greek anti (αντί), "like," and rhis (ῥίς, ινοϛ), "nose", inus (-ινοϛ), "of" or "pertaining to"; thus, "like a nose", possibly referring to the nose-like capsule in its mature state.
Snapdragons are often considered as cold-season annual plants and do best in full or partial sun, in well drained soil (although they do require regular watering). They are classified commercially as a range of heights: dwarf (6-8 inches), medium (15-30 inches) and tall (30-48 inches).
The Snapdragon is an important garden plant, widely cultivated from tropical to temperate zones as a bedding, rockery, herbaceous border or container plant. (Tolety 2011) Cultivars have showy white, crimson, or yellow bilabiate flowers (with two lips). It is also important as a model organism in botanical research, and its genome has been studied in detail.
Antirrhinum is a genus that has been used from the earliest genetic studies of Mendel and Darwin and was used as a model by Erwin Baur (Tolety 2011) and is a typical example of incomplete dominance by the red allele with the anthocyanin pigment. 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.
Several species of Antirrhinum are self-incompatible, meaning that a plant cannot be fertilised by its own pollen. Self-incompatibility in the genus has been studied since the early 1900s. Self-incompatibility in Antirrhinum species is controlled gametophytically and shares many important features with self-incompatibility systems in Rosaceae and Solanaceae.
In addition to growing the plants for cut flowers, the seeds have been used to extract edible oils, particularly in Russia, while the leaves and flowers have been considered to possess antiphlogistic properties and have been used in poultices. A green dye has also been extracted from the flowers. (Tolety 2011)
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- USDA: Plants database
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- Oyama, R. K.; Baum, D. A. (2004). "Phylogenetic relationships of North American Antirrhinum (Veronicaceae)". American Journal of Botany 91 (6): 918–925. doi:10.3732/ajb.91.6.918. PMID 21653448.
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- Albach, D. C.; Meudt, H. M.; Oxelman, B. (2005). "Piecing together the "new" Plantaginaceae". American Journal of Botany 92 (2): 297–315. doi:10.3732/ajb.92.2.297. PMID 21652407.
- Tolety J, Sane A. Antirrhinum , in Kole C (ed.) Wild Crop Relatives: Genomic and Breeding Resources. Plantation and Ornamental Crops. Springer 2011, pp. 1-14
- Antirrhinum in Topwalks
- The Genus Antirrhinum (Snapdragon): A Flowering Plant Model for Evolution and Development
- Antirrhinum majus genetic and phenotypic database
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