Scientists have identified a 125 million- to 130 million-year-old freshwater plant, a contemporary of dinosaurs, as one of earliest flowering plants on Earth.
The finding, represents a major change in the presumed form of one of the planet's earliest flowers, known as angiosperms, researchers said.
"This discovery raises significant questions about the early evolutionary history of flowering plants, as well as the role of these plants in the evolution of other plant and animal life," said David Dilcher, paleobotanist at the Indiana University in US.
The aquatic plant, Montsechia vidalii, once grew abundantly in freshwater lakes in what are now mountainous regions in Spain.
Fossils of the plant were first discovered more than 100 years ago in the limestone deposits of the Iberian Range in central Spain and in the Montsec Range of the Pyrenees, near the country's border with France.
Also previously proposed as one of the earliest flowers is Archaefructus sinensis, an aquatic plant found in China.
"A 'first flower' is technically a myth, like the 'first human,'" said Dilcher.
"But based on this new analysis, we know now that Montsechia is contemporaneous, if not more ancient, than Archaefructus," he said.
"The reinterpretation of these fossils provides a fascinating new perspective on a major mystery in plant biology," said Donald H Les, a professor of ecology and evolutionary biology at the University of Connecticut.
"David's work is truly an important contribution to the continued quest to unravel the evolutionary and ecological events that accompanied the rise of flowering plants to global prominence," he said.
The conclusions are based upon careful analyses of more than 1,000 fossilised remains of Montsechia, whose stems and leaf structures were coaxed from stone by applying hydrochloric acid on a drop-by-drop basis.
The plant's cuticles - the protective film covering the leaves that reveals their shape - were also carefully bleached using a mixture of nitric acid and potassium chlorate.
The age of the plant at 125 million to 130 million years is based upon comparisons to other fossils in the same area, notably the freshwater algae charophytes, which places Montsechia in the Barremian age of the early Cretaceous period, making this flowering plant a contemporary of dinosaurs such as the brachiosaurus and iguanodon.
"Montsechia possesses no obvious 'flower parts,' such as petals or nectar-producing structures for attracting insects, and lives out its entire life cycle under water," Dilcher said.
"The fruit contains a single seed" - the defining characteristic of an angiosperm - "which is borne upside down," he said.
The study was published in the journal