Dahlia is a genus of bushy, summer- and autumn-flowering, tuberous perennials that are originally from Mexico, where they are the national flower. The Spanish discovered dahlias in the mountains of Mexico.
In 1872 a box of Dahlia roots were sent from Mexico to the Netherlands. Only one plant survived the trip, but produced spectacular red flowers with pointed petals. Nurserymen bred from this plant, which was named Dahlia juarezii with parents of Dahlias discovered earlier and these are the progenitors of all modern Dahlia hybrids. Ever since, plant breeders have been actively breeding Dahlias to produce thousands of cultivars, usually chosen for their stunning and brightly coloured flowers. The great variety results from Dahlias being octoploids (they have eight sets of homologous chromosomes, whereas most plants have only two).
Dahlias are used as food plants by the larvae of some Lepidoptera species including Angle Shades, Common Swift, Ghost Moth and Large Yellow Underwing.
The dahlia is named after Swedish 18th-century botanist Anders Dahl.
The dahlia is the official flower of the city of Seattle.