Identification of a tetrahedral apical cell preserved within a fossilized fern fiddlehead

Rafael da Silva Cruz*, Alexander J. Hetherington*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Summary The gradual unfurling of fronds from tightly coiled tips, termed fiddleheads or croziers, is one of the most recognizable features of the fern lineage, but its evolutionary origin remains unclear. Here, we identify that fiddleheads and their development, termed circinate vernation,1,2 are not ubiquitous across ferns. Instead, they are a synapomorphy of a clade we term the circinatophytes that includes extant marattioid and leptosporangiate ferns. Circinatophytes encompass the vast majority of extant ferns,3 and fossil evidence demonstrates the antiquity of the group at over 315 million years. Despite their overall conservation, a comparative investigation of extant species suggests that during fiddlehead evolution, there was a transition from a tetrahedral to a wedge-shaped apical cell in the leaf meristem. We predict that a tetrahedral leaf apical cell was likely ancestral in circinatophytes, despite being present in less than 2% of modern species,3 and that this cell mirrored the tetrahedral cell found in the shoots of all major groups of ferns. This is supported by our description of a tetrahedral apical cell in, to our knowledge, the oldest preserved fossil fern leaf meristem of the ca. 315-million-year-old fern Ankyropteris corrugata. We conclude that fiddleheads have been highly conserved in the circinatophytes, and the similarities in leaf and shoot apical cells in early diverging groups of ferns add support to the hypothesis that fern leaves evolved through the modification of shoots, as proposed by the telome theory.4
Original languageEnglish
Number of pages11
JournalCurrent Biology
Early online date5 Dec 2024
DOIs
Publication statusPublished - 20 Jan 2025

Keywords / Materials (for Non-textual outputs)

  • ferns
  • fronds
  • leaf evolution
  • leaf development
  • fiddlehead
  • fossil plants
  • Carboniferous
  • apical cells
  • leaf apical meristem
  • telome theory

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