Etymology

The genus Dahlia is named in honour of Swedish botanist A. Dahl and imperialis means “imperial, magnificient” in Latin.

Description and flowering period

It is an erect herbaceous perennial reaching 4 meters in height in cultivation and even more within its natural habitat (where it can be found at elevations of up to 1 700 meters). The species is characterised by its fleshy underground tubers and large purple hollow stems which carry a flush of bright green compound leaves, each bearing 7 oval veined leaflets with toothed margins. In a similar way to all others in the Aster or Composite family, the actual flowers – called florets – are minuscule and regrouped in a composite inflorescence referred to as a “capitulum” which, when viewed from a distance, may have the appearance of being a single flower. Each inflorescence can bear up to 30 of these composite flowers. The peripheral flowers, resembling petals, can be white, pink or lavender whilst the florets are orange in colour.

Habitat

It is suitable for any rich yet free-draining soil in a sunny position. In case of frosts, the stems will perish and the plant will enter dormancy until the following spring.

Uses

Ornamental, often used at the back of beds or against a south facing wall.
Food-crop: The young underground tubers – tasting like artichoke – can be used in soups or oven-baked…
Medicinal: The tubers are rich in fibres and insulin and have been used to control diabetes and to prevent colon cancer by the Amerindian people.
Crafts: The petal were used by the Amerindian people to dye fabrics.

Notes

The flower has been the emblem of the city of San Francisco since 1926 and the national flower of Mexico since 1963.

Translated by: François Saint-Hillier – MNHN