Fibonacci leaf spirals were an ancient pattern inherited from the earliest leafy land plants.

Fibonacci spirals dominate the arrangement of leaves and other organs in living plants. Because the pattern appears across the major groups of land plants, it was natural to picture it as an ancient developmental rule inherited from very early leafy ancestors.

The fossil record could not easily test that idea. Phyllotaxis is a three-dimensional pattern, and flattened or incomplete fossils often do not preserve enough of a stem to follow a spiral accurately.

In 2023, researchers reconstructed shoots of Asteroxylon mackiei, a 407-million-year-old lycophyte from the Rhynie chert. Lycophytes belong to one of the earliest branches of vascular plants to evolve leaves. The reconstructions showed whorls and several kinds of spirals—but every spiral they could trace was non-Fibonacci.

One fossil species cannot tell us the arrangement of every early land plant. It does show that Fibonacci spirals were not an invariant feature of the earliest leafy lineages.

Later evolutionary work has strengthened the alternative picture: Fibonacci-dominated phyllotaxis appears to have arisen after the first leaves and probably evolved independently in lycophytes and in the lineage leading to ferns and seed plants.