The history of dahlias
Internationally renowned New Zealand-based ornamental plant breeder Dr Keith Hammett shares the botanical back story of this remarkable plant genus.
Dr Keith Hammett shares a fascinating botanical back story.
What is really important is that two species of Dahlia that were separated geographically from each other in Mexico were brought together in the Botany Garden in Madrid.
In an ideal world, when someone becomes serious about breeding a particular genus of plant, they would visit the plant in its natural habitat.
Idid this when I visited Mexico in 1989, at which point I had been breeding the hybrid garden Dahlia for thirty years and having written a book on the plant.
It is important to understand that when a plant is first introduced to cultivation, only a tiny fragment of genetic variability is captured. Many garden plants have a frighteningly narrow genetic base.
There are several reasons for this. Historically transport by sailing ship from one continent to another was slow and it was difficult to keep plants alive. Many species have evolved to occupy discrete ecological niches and do not cover vast tracts. Therefore it was often chance when someone other than the people native to an area would stumble on a plant near a town or road and would want to send it back to their home country. This includes plant hunters specifically sent out to find new plants.
Such is the case with Dahlia. I found that although Mexico is near the equator, different species occur at different altitudes on the mountain ranges where it can be quite chilly even mid-summer. This explains why Dahlias are not heat tolerant and do best in climates such as those found in the UK or Pacific Northwest of the USA.
The genus Dahlia is found virtually only within Mexico. By 1521, the Aztec Empire had been defeated by the invading Spanish under the leadership of Cortés. Subsequently, everything native was systematically destroyed. For this reason we have very little knowledge regarding any involvement of the Aztec people with the plant.
What is significant is that within half a century of the conquest, plants of the genus Tagetes were reported to be growing on the coast of North Africa, hence the common name African Marigold for Tagetes erecta, despite it being a native of Mexico.
In contrast it was not until 1789, the year of the French Revolution, that species of Dahlia were sent from Mexico to Spain – more than two and a half centuries after the conquest. This suggests that the marigold was cultivated by and was important to the Aztecs, while the Dahlia was not.
In 1786 a Royal Botanical Expedition was sent to Mexico by the Spanish King to quantify the plants growing in New Spain and to establish a botanic garden in Mexico City. It was as a consequence of plants being collected for the botanic garden that plant material was sent back to Spain.
What is really important is that two species of Dahlia that were separated geographically from each other in Mexico were brought together in the Botany Garden in Madrid and were able to hybridise. By chance, both species each had each pair of their chromosomes duplicated. They were tetraploids and as a consequence, the resulting hybrid ended up with four copies of each