Article by: Charles Fatima, on 07 July 2023, at 08:01 am PDT

In a stunning revelation, scientists have discovered an extraordinary arrangement of leaves that defies the famous Fibonacci sequence, casting doubt on long-held beliefs regarding the origins of spiral patterns in plants.

The Fibonacci sequence, a mathematical marvel, follows a pattern in which each number is the sum of the two preceding numbers: 1, 1, 2, 3, 5, 8, 13, and so on. Remarkably, many modern plants exhibit spiral patterns that align with Fibonacci numbers, manifesting in the graceful arrangement of succulent leaves, the bracts of pinecones, or the enchanting symmetry of a sunflower's seeds.

Given the prevalence of these Fibonacci spirals in today's plant kingdom, scientists had previously assumed that such patterns must have evolved in the earliest land plants. However, a study published in the journal Science on June 16 challenges this prevailing notion. Researchers discovered that the leaves of an ancient plant, belonging to one of the earliest known groups to develop leaves, showcased spiral arrangements that defied description by Fibonacci numbers.

"This study helps us understand how the diversity of plants has been generated," remarks esteemed botanist Barbara Ambrose, Director of Laboratory Research at the New York Botanical Garden, who was not directly involved in the research. The findings illuminate the intricate mechanisms underlying the evolution of plants, shedding light on the fascinating tapestry of botanical wonders.

In plants featuring spiral leaf patterns, the leaves can be described by sets of curved lines spiraling both clockwise and counterclockwise from the center. When the numbers of clockwise and counterclockwise spirals align with Fibonacci numbers, it is referred to as Fibonacci spiraling. While the reasons for the prevalence of Fibonacci spirals in modern plants remain uncertain, some theories suggest that they optimize space utilization or arise from the distribution of auxins, a type of plant growth hormone.

To unravel the enigma, Sandy Hetherington, a paleobotanist from the University of Edinburgh, and her colleagues turned to the fossils of Asteroxylon mackiei—an extinct member of the lycopod group, which encompasses modern club mosses. These fossilized remains were carefully extracted from the Rhynie chert, a remarkable 400-million-year-old sedimentary rock formation in Aberdeenshire, Scotland. The Rhynie chert is renowned for its exceptional preservation of some of the earliest land plants.

By digitally reconstructing cross-sectional images of the A. mackiei fossils collected in 1969, Hetherington and her team brought the ancient plants back to life in stunning 3D representations. Astonishingly, two out of the four reconstructed plants exhibited leaf arrangements that deviated from Fibonacci spirals. While both plants displayed eight counterclockwise spirals (a Fibonacci number), one had seven clockwise spirals, and the other had nine—neither of which conformed to Fibonacci numbers.

Even more perplexing, the remaining two plants eschewed spirals altogether, instead boasting a series of rings stacked along their stems, defying conventional expectations. Holly-Anne Turner, a paleontologist and co-author of the study, expresses surprise, saying, "Given the prevalence of Fibonacci spirals today and in the later fossil records of plants, we definitely expected Fibonacci spirals." Notably, these A. mackiei fossils predate other lycopod fossils with non-Fibonacci spiraling by nearly 50 million years.

The revelation that some modern lycopods do exhibit Fibonacci spiraling while their ancient counterparts do not suggests that spiraling patterns may have independently evolved in different lineages of plants. Peter Crane, a prominent botanist, and president of the Oak Spring Garden Foundation, who was not involved in the study, emphasizes the significance of this finding and how it reshapes our understanding of plant evolution.

However, Ambrose cautions against drawing definitive conclusions from the study, highlighting the need to examine a wider range of early plants to glean further insights into the evolution of spiraling patterns in nature. Moreover, with advancements in computing technology, revisiting hand-analyzed fossils from decades ago presents an exciting opportunity. The wealth of information and intricate details that can now be extracted through computer simulations may hold unforeseen revelations, unlocking untold botanical secrets.

The study was published on 16th June 2023 in Science.