Delicate and upturned, with curving petals arranged in threes, it looks like the subject of a Monet painting. In fact, it is what scientists believe the bloom of the last common ancestor of all living flowers looked like.

Flowering plants – or angiosperms – are thought to make up about 90% of all living land plants. There are more than 300,000 different species on the planet, from tiny forget-me-nots to glorious magnolias.

But while flowering plants are thought to have emerged between 140m and 250m years ago, there are no fossil flowers more than 130m years old, making it challenging to work out what the first flowers might have looked like.

“We almost know nothing about how flowers evolved since their origin and yet this is extremely important for their ecological role and the role that plants play today on Earth,” said Hervé Sauquet, an evolutionary biologist and first author of the new study from Paris-Sud University.

The evolution of flowering plants also foxed Darwin, who described their sudden diversification as an “an abominable mystery”.

But now Sauquet and an international team of researchers say they have unravelled an important piece of the puzzle – the structure of the ancestral flower.

Writing in the journal Nature Communications, the team describe how they constructed a family tree of flowering plants based on genetic data from 792 species, and mapped the structural characteristics of the plants’ flowers.

To trace back the evolution of flowers, the new study used the evolutionary tree (here simplified) that connects all living species of flowering plants. Photograph: Hervé Sauquet & Jürg Schönenberger.

They then explored the structure of flowers at each branching point on the family tree and traced back to explore what the blooms of the last common ancestor of all flowering plants would have looked like. The process was repeated using family trees produced using different methods to check whether the results held.

The upshot is a delicate-looking flower with rings of upturned petals. “This is what we infer to be the ancestral flower of all living flowering plants,” said Sauquet.

Like most modern flowers, the ancestral flower has both male and female parts. Beverley Glover, professor of plant systematics and evolution at the University of Cambridge and who was not involved in the study, said the finding was exciting, since there is a species alive today that comes from an early branch on the angiosperm family tree. However, this species, known as Amborella, has separate male and female flowers.

The study also reveals that the ancestral flower’s stamens, petals and sepals – protective petal-like parts – were arranged not in spirals but concentric circles called whorls, with three petals or sepals in each.

That, says Sauquet, overturns a long held idea that such structures in early flowers had a spiral arrangement which gave way to the whorled configuration that is prevalent today. “I think many people are not going to believe us at first,” he said.



The model also suggests the ancestral flower would have had three or four such whorls for each organ, although most living flowers today have fewer. “To get to the living flowers it is very simple; just get rid of some whorls,” said Sauqet, adding that as only one whorl of sepals for protection and one of petals to attract pollinators is needed for a functional flower, having more might have been a waste of the plant’s resources.



Furthermore, he said, a reduction in the number of whorls might have given rise to structural changes that made for more efficient pollination, for example by making it easier for pollinators such as bees to approach.

“Working out why this might have happened will keep us scratching our heads for some time,” said Glover.



But not everyone was as enthusiastic about the study. William Crepet, a plant biologist at Cornell University, said that while he had some reservations about the model, the results were interesting and raise questions about the ancestry of the flowering plants.



Glover conceded that the team’s findings were still only a set of predictions, but said the study incorporated swaths of data, making them the best yet.