Scientists have found one of the oldest known examples of a winged seed, providing valuable information about how plants first adapted to disperse their seeds through the wind.
Scientists have found one of the oldest known examples of a winged seed, providing valuable information about how plants first adapted to disperse their seeds through the wind.
The research, published today as the final Version of Record after being previously shared as a Reviewed Preprint in eLife, details the second-oldest known winged seed called Alasemenia. This seed dates back to the Late Devonian period, approximately 360 to 385 million years ago. The researchers utilized strong mathematical analysis to demonstrate that the three-winged design of Alasemenia is more efficient for wind dispersal compared to one, two, and four-winged seeds.
Wind dispersal is a natural phenomenon that helps plants spread their seeds by air to various locations. This strategy reduces competition for resources and enhances the survival chances of the plant. Some common examples of wind dispersal methods include tumbleweeds, parachute seeds like dandelions and milkweeds, as well as the winged seeds of maple trees, often referred to as ‘helicopter’ seeds.
The earliest known seeds from plants emerged during the Late Devonian epoch. “This era represents a crucial evolutionary step in plant development, marking a shift from spore-based reproduction, as seen in ferns and mosses, to seed-based reproduction,” explains lead author Deming Wang, a professor at the Key Laboratory of Orogenic Belts and Crustal Evolution, Department of Geology, Peking University, Beijing, China. “However, there’s still little knowledge about how seeds dispersed by wind during this time since many fossils lacked wings and typically had a protective cupule.”
Cupules are cup-like structures that partially encase seeds, similar to acorns or chestnuts (though the Devonian cupules do not share the same ancestry as modern ones). These structures may relate to other methods of dispersal, such as water transport.
To gain a deeper understanding of early wind dispersal, Wang and his team examined several seed fossils from the Late Devonian located at the Jianchuan mine in Xinhang Town, Anhui Province, China. They identified a new fossil seed named Alasemenia.
The researchers characterized Alasemenia by meticulously analyzing the fossil samples and making slices to inspect the seed’s internal structures. They discovered that Alasemenia seeds are between 25 to 33 mm long and distinctively lack a cupule, in contrast to most other seeds from that time. This discovery represents one of the oldest known instances of a seed without a cupule, dating back 40 million years earlier than previously thought. Each seed is covered by a seed coat that extends outward into three wing-like lobes. These wings taper to points and curve outward, forming broad, flat shapes that would help the seeds capture the wind.
The team also compared Alasemenia with other known winged seeds from the Late Devonian, namely Warstenia and Guazia. Both of these seeds possess four wings, with Guazia featuring broad, flat wings and Warstenia having short, straight wings. Through quantitative mathematical analysis, they assessed which seed design provided the best wind dispersal. This analysis revealed that having an odd number of wings, as found in Alasemenia, allows for more stability and a higher spin rate as the seeds fall from their branches, making it easier for them to capture the wind and travel further from the parent plant.
“Our discovery of Alasemenia increases our understanding of the evolution of wind dispersal methods in early land plants,” says senior author Pu Huang, an assistant research fellow at the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing, China. “Alongside our existing knowledge of Guazia and Warsteinia, we conclude that the development of winged seeds due to integument outgrowth was the earliest wind dispersal strategy during the Late Devonian, occurring before methods like parachutes or plumes emerged.”
“The three-winged seeds observed in Alasemenia during the Late Devonian would eventually lead to the evolution of two-winged seeds in the Carboniferous period, followed by single-winged seeds in the Permian,” Wang adds.
