A 407-million-year-old fossil is forcing botanists to rethink one of nature's most famous laws. Asteroxylon mackiei, an extinct plant found in the Rhynie chert in Scotland, had leaves arranged in spirals that did not follow the Fibonacci sequence. The study, published in Science, overturns the idea that this mathematical organization was present since the first land plants.
When nature doesn't follow the script
The Fibonacci sequence is everywhere. Sunflowers, pine cones, pineapples, cacti: 90% of modern plants organize their organs according to this numerical progression (1, 1, 2, 3, 5, 8, 13, 21, etc.). Each organ emerges at 137,5 degrees from the previous one, creating continuous clockwise and counterclockwise spirals. The numbers of these spirals are always consecutive in the series.
Until now, it was thought that this rule was as old as plants themselves. A legacy preserved for hundreds of millions of years, passed down from the first land plants to the flowers we grow today. But Asteroxylon mackiei tell another story.
Holly-Anne Turner, first author of the study and PhD student atUniversity College Cork, examined 3D reconstructions of the fossil's cross-sections. The result: some showed eight counterclockwise spirals and thirteen clockwise (Fibonacci) spirals.
Others had seven or nine (non-Fibonacci) spirals. Two specimens even had no spirals at all, but rather concentric rings of leaves along the stem.
Rhynie, a window on the Devonian
The fossil deposit of Rhynie, in Aberdeenshire, Scotland, is one of the most important paleontological sites in the world. Here, 407 million years ago, a primordial terrestrial ecosystem was suddenly sealed in silica. The result is extraordinary cellular preservation: tissues, meristems, and even parasitic fungi are visible under the microscope.
Asteroxylon mackiei It is the most complex plant found at this site. It belongs to the lycophytes, an ancient group that includes modern selaginella plants. It had leafy stems, root-bearing axils, and a primitive root system. It is similar to the ferns, but with an older history and a less orthodox structure.
Non-Fibonacci Spirals: The Detail That Changes Everything
The team led by Alexander Hetherington ofUniversity of Edinburgh used digital reconstruction techniques to produce the first 3D models of the leaf buds of AsteroxylonThey analyzed 20 fossil specimens, tracing the whorls of leaves along the stems.
The spirals observed were all of the type n:(n+1), a mathematical category rare today but apparently common in the Lower Devonian. It means that the numbers of clockwise and counterclockwise spirals were not consecutive in the Fibonacci sequence, but followed other progressions.
As Hetherington explains:
"The technology to 3D print a 407-million-year-old fossil and hold it in your hand is truly incredible. Our results offer a new perspective on the evolution of Fibonacci spirals in plants."
The study suggests that the Fibonacci spirals were not a conserved ancestral trait, but an evolutionary innovation that emerged separately in different plant groups. Lycophytes such as Asteroxylon They followed an evolutionary path distinct from ferns, conifers, and flowering plants.
Why is Fibonacci so common today?
The question remains open. If the first leafy plants didn't use Fibonacci, why do 90% of modern plants do? The answer probably lies inefficiencyFibonacci spirals maximize sunlight exposure, optimize rainwater distribution, and minimize shading between adjacent organs.
But this efficiency wasn't necessary 407 million years ago. The first land plants grew in environments with little competition. The selective pressure for geometric optimization was less. Only with increasing plant density and ecosystem complexity did Fibonacci become a decisive evolutionary advantage.
Uno 2023 study I read on GreenMe had already hypothesized that non-Fibonacci spirals were more common than we thought in ancient plants. The discovery on Asteroxylon confirms this intuition.
Two separate evolutionary paths
The discovery has profound implications for the biology Evolutionary. It indicates that the leaves of ancient lycophytes had a completely different evolutionary history than other plant groups. This is not a branching from a common ancestor with Fibonacci integrated into the DNA, but rather parallel and independent evolutions.
Turner adds:
“The lycophyte Asteroxylon mackiei It is one of the earliest examples of a plant with leaves in the fossil record. Using these reconstructions, we were able to trace the individual spirals of leaves around the stems. Our analysis shows that primitive lycophytes developed non-Fibonacci spiral patterns.”
This means that when we look at a sunflower or a pine cone, we're seeing the result of a long process of evolutionary optimization. But 400 million years ago, the plant world was an experimental laboratory where the rules were still being tested.
In short, the mathematics of nature has not always been the same. And perhaps, in other ecosystems or other geological eras, there existed (or will exist) plants with geometries we can't even imagine today.
Better to keep your eyes open. And your mind, too.
