A 407-million-year-old fossilized plant is challenging scientists’ prior assumptions about plant evolution. While most contemporary plants showcase spiral patterns aligned with the renowned Fibonacci sequence, this ancient plant’s leaves do not conform to these established patterns.
This revelation is reshaping discussions on plant diversity and development.
The Fibonacci sequence is a series where each number is the sum of its two predecessors, such as 1, 1, 2, 3, 5, 8, 13, etc. This sequence can be observed in nature in the way leaves are arranged in certain succulents, the formation of a pinecone’s bracts, or the seed pattern in sunflowers.
In plants with these spiral patterns, if both clockwise and counterclockwise curved lines detailing the leaves align with the Fibonacci sequence, it’s termed ‘Fibonacci spiraling’.
The reason most plants exhibit this arrangement is still uncertain, though hypotheses suggest it could optimize space between leaves or be influenced by auxin distribution, a plant growth hormone.
In this groundbreaking study, Sandy Hetherington, a paleobotanist from the University of Edinburgh, and her team delved into the fossils of Asteroxylon mackiei, a primitive plant from the lycopod group, which also consists of modern-day club mosses.
These fossils were sourced from Scotland’s Rhynie chert, a sedimentary rock deposit known for preserving some of the earliest terrestrial plants. While previous studies in 1969 had taken cross-sectional images of these fossils, Hetherington and her team employed digital techniques to recreate 3-D models of the original plants.
The results were intriguing. Out of the four reconstructed plants, two showed non-Fibonacci spiraling.
They had eight counterclockwise spirals (a Fibonacci number), but the clockwise spirals were seven in one and nine in the other, neither of which belongs to the Fibonacci series. The remaining two plants had leaves growing in stacked rings rather than spirals.
Interestingly, even though lycopod leaves have an independent evolutionary lineage, some modern lycopods manifest Fibonacci spiraling. This finding hints that Fibonacci spirals might have evolved distinctively in separate plant lineages. Peter Crane, a botanist uninvolved in the study, emphasized this point.
Barbara Ambrose, a botanist, cautioned that A. mackiei represents just one species, and with a fragmented fossil record, studying more ancient plants could provide richer insights into spiral evolution. She also highlighted the potential of modern computational tools in reanalyzing old fossils previously examined by hand.