The ‘original ancestral flower’

Flowering plants appeared only about 140 million years ago, but since then they have diversified spectacularly. In fact, they are by far the most diverse group of plants on Earth.

No one knows exactly how this happened – their origin and early evolution remains one of the biggest enigmas in biology – but a new study has shed new light on what the earliest flowers might have looked like.

The eFlower project

The study, the ‘eFLOWER project’, is an unprecedented international effort to combine information on the structure of flowers with the latest information on the evolutionary tree of flowering plants, based on their DNA.

Among the most surprising findings is a new model of the ‘original ancestral flower’ that doesn’t match any of the ideas proposed to date.

‘When we finally got the full results, I was quite startled until I realized that they actually made good sense. No one has really been thinking about the early evolution of flowers in this way, yet so much is easily explained by the new scenario that emerges from our models.’

HERVÉ SAUQUET
Leader of the study and an associate professor at Université Paris-Sud

A new vision of floral evolution

According to the new study, the ancestral flower was bisexual, with both female (carpels) and male (stamens) parts, and with multiple whorls (concentric cycles) of petal-like organs in sets of threes.

About 20% of flowers today have these ‘trimerous’ whorls, but typically fewer: lilies have two, magnolias have three. It has long been assumed that the ancestral flower had all organs arranged in a spiral.

‘These results call into question much of what has been thought and taught previously about floral evolution!’

JUERG SCHOENENBERGER
Professor at the University of Vienna

The researchers also reconstructed what flowers looked like at all the key divergences in the flowering plant evolutionary tree, including the early evolution of monocots (such as orchids, lilies and grasses) and eudicots (such as poppies, roses and sunflowers), the two largest groups of flowering plants.

‘The results are really exciting! This is the first time that we have a clear vision for the early evolution of flowers across all angiosperms.’

MARIA VON BALTHAZAR
Senior scientist and specialist of floral morphology and development at the University of Vienna

Questions remain

The study offers a simple, plausible scenario to explain the spectacular diversity of floral forms. Nevertheless, many questions remain.

The fossil record of flowering plants is still very incomplete, and scientists have not yet found fossil flowers as old as the group itself.

Peter Crane, president of the Oak Spring Garden Foundation and a colleague familiar with the results of the study, said that the study is a ‘very important step toward developing a new and increasingly sophisticated understanding of the major patterns in the evolution of flowers’, adding that it reflects ‘great progress’.