With the incredible diversity of flowers that exist today—from pinprick-sized duckweed to the meters-high blooms of a corpse flower—it’s hard to imagine that they all descend from just a single species. Charles Darwin himself wrung his hands over how flowering plants exploded in diversity early in their evolution. Now, researchers have figured out what the ancestral flower might have looked like. The study may help them uncover how flowers took over the world.
Fossils are the surest way to learn about organisms that lived in the past, but these are hard to come by for early flowers: The earliest preserved blossoms date back some 130 million years—at least 10 million years after the time when researchers think the ancestor of all flowering plants was alive. But there is another way to learn about species that are long gone: by taking a careful look at the forms of their modern descendants, and tracing the history of those forms back to the trunk of their family tree.
To that end, dozens of researchers participating in the eFLOWER project amassed data from scientific papers to create the largest database of the structures of modern flowers, like their sexual organs and the layouts of their petals. The analysis included more than 13,000 data points spanning back to a 1783 description by famous evolutionary biologist Jean-Baptiste Lamarck. Combining those data with a DNA-based family tree and information about fossils, the scientists tested millions of configurations of how flowers may have changed through time to determine the most likely structure and shape for the earliest flowers.
Though the team’s reconstructed ancestral flower doesn’t look radically different than many modern flowers, it does have a combination of traits not found today. Like many of today’s flowers, the putative ancestor contained both male and female parts on the same blossom. And the arrangement and numbers of its petals and its organs that shed and receive pollen all fall within the range of its modern descendants—no one trait stands out as obviously ancient. But no one current flower matches its form exactly, either. One discovery that will surprise some researchers is that its petals and other organs were organized in concentric circles in groups of three, rather than in spirals, the team reports today in Nature Communications.
Some of the earliest surviving branches in the family tree of flowering plants, such as the ancient Amborella shrub, have their petals arranged in spirals. Many researchers have assumed that the first flower was the same. But Hervé Sauquet, an evolutionary biologist at the University of Paris Sud, compares these plants to the ancient mammal group that contains platypuses—odd, egg-laying aquatic mammals living in Australia. Though some of their traits are likely remnants of their ancient origins, they’re also reflective of hundreds of millions of years of later evolution to their specific environments. “We’re just showing this applies to Amborella as well,” Sauquet says.
Chuck Bell, an evolutionary plant biologist at the University of New Orleans in Louisiana, praises the way the work synthesizes so many different types of data, from DNA to fossils to the structures of modern flowers. “In that sense it’s amazing,” he says. But it also comes with uncertainty, not least because many of history’s flowering plants can no longer be studied. “A lot of species died in the last couple hundred million years,” notes Alex Harkess, an evolutionary botanist at the Donald Danforth Plant Science Center in St. Louis, Missouri.
As for Darwin’s question, the study hints at a counterintuitive answer: It may be that early flowers became more diverse not by evolving greater complexity, but by initially becoming simpler. Remove just a few components from this ancestor, Sauquet says, “and very quickly we could build half the diversity of living flowers.”