Genetics unlocks secrets of world's largest flower
Saturday January 13, 2007
By Steve Connor
The origin of the world's largest flower has been tied down to a family of plants that have unusually small flowers.
A genetic analysis of rafflesia, which produces giant flowers 1m across, has finally solved the botanical mystery of where this plant belongs in the tree of life.
Studies of rafflesia's DNA show that it is closely related to the Euphorbiaceae family of plants that includes poinsettias, rubber trees, castor oil plants and cassava.
Rafflesia lives a parasitic existence on the floor of the jungles of Southeast Asia and has no leaves, shoots or roots, but produces enormous flowers with a strong smell of rotting flesh to attract pollinating blowflies.
The unusual nature of rafflesia's anatomy has made it virtually impossible for botanists to classify it or to determine which ancestral stock of plants it evolved from more than 46 million years ago.
Charles Davis of Harvard University, who led the study published in the journal Science, said that rafflesia's lineage had confounded scientists since the plant was discovered by European explorers 180 years ago.
"As a parasite living inside the tissue of a tropical vine, the plant lacks leaves, shoots or roots, making it difficult to compare to more conventional plants," Dr Davis said.
"Most efforts to place plants in the botanical tree of life in the past 25 years have tracked ancestry using molecular markers in genes governing photosynthesis.
"Rafflesia is a non-photosynthetic parasite, and those genes have apparently been abandoned, meaning that to determine its lineage we had to look at other parts of the plant's genome."
The Euphorbiaceae family have notoriously small flowers of just a few millimetres in diameter, so at some point in the rafflesia's evolution its flowers must have gone through a growth phase equivalent to an increase in size of 79 times the original dimensions.
The rafflesia's carcass-like appearance imitates a recently killed animal, making it attractive to carrion flies.