Plant 355

Dahlia species (Asteraceae)


Dahlia, a small genus of herbaceous perennials native to Mexico and Central America, is commonplace among late-summer plants in European gardens. Centuries of artificial breeding has transformed the appearance of garden dahlias compared to their wild relatives.

Unpicking the inheritance of dahlia colour was a surprising success for the science of genetics in its twentieth-century infancy. Anthocyanins produce magenta, purple, crimson and scarlet, chalcones and aurones produce yellows, and flavones and flavanones produce ivory pigments. Interactions among these pigments contribute to the hundreds of distinctive, named garden dahlia cultivars. Moreover, changes to the appearance of the hundreds of tiny flowers that make up a dahlia flowerhead may lead to dramatic differences in overall appearance compared to the typical daisy-like wild dahlia.

The earliest mention of dahlia appears to be in the Codex Badianus or the Libellus de Medicinalibus Indorum Herbis; the first illustrated, botanical text written in the post-Columbian Americas. The Codex is a Latin translation of an Aztec botanical and medicinal text, including plants of Aztec gardens, written by the Christianised Aztec Martín de la Cruz in 1552. However, the highly stylised images can be interpreted as multiple different members of the Asteraceae. Not only does this document provide historical evidence for dalhia’s Mexican origin, it has, by stretching the limits of the evidence, been used to state dahlia was Aztec emperor’s Moctezuma II’s (c.1466-1520) favourite flower. In another empire, Empress Joséphine (1763-1814) was protective of the dahlias in her garden at the Château de Malmaison, Paris, leading to claims it was her favourite flower. Yet looking at the work of Pierre-Joseph Redouté (1759-1840), the botanical artist most closely associated with the Empress’s garden, one might conclude roses had a greater claim to her affections. The dahlia was adopted by Mexico as its national flower in 1963.

In Europe, dahlias are considered ornamental. In pre-Hispanic Central America, they were also food plants. Consumption of the tubers, rich in inulin, a fructose polymer that is one the fructans, was not adopted outside the plant’s native range.

When the Spanish botanist Antonio Cavanilles (1745-1804) named the genus, he commemorated the Swede Andreas Dahl (1751-1789) rather than adopt one of the plant’s indigenous names. Should the genus be pronounced day-LEE-a or dar-LEE-a? Botanical conventions over pronunciation of Latinised proper names means the latter would be correct. The former is quite a different genus, named after the eighteenth-century English apothecary Samuel Dale (c.1659-1739).

Further reading

Coats AM 1977. The Empress Joséphine. Garden History 5: 40-46.

Ohno S et al. 2014 Genetic control of anthrocyanin synthesis in dahlia (Dahlia variabilis). In Ramawat KG and Mérillon JM (eds.) Bulbous plants biotechnology. CRC Press, pp. 228-247.

Sorensen PD 1970. The dahlia: an early history. Arnoldia 30: 121-138.

Stephen Harris