The ancient seed ferns that redefined the Carboniferous period as an age of discovery

Gardening · Published 3 October 2026 Swipe more like this →

In short: Pteridosperms were once thought to be simple transitional fossils between ferns and cycads. Today, we know these extinct seed-producing plants are a diverse, polyphyletic group that fundamentally changed our understanding of prehistoric flora. Discover why these fern-like giants are still central to the study of plant evolution.

In the late 19th century, palaeobotanists noticed that many Carboniferous fossils resembling fern fronds possessed anatomical features more similar to modern cycads. Henry Potonié coined the term Cycadofilices in 1899 to describe these supposed intermediates. However, the true nature of these plants was revealed shortly after by Frank Oliver, Dukinfield Henry Scott, and Marie Stopes. By identifying identical glandular hairs on both the fronds of Lyginopteris and the seeds of Lagenostoma, they proved that these structures belonged to the same organism, effectively identifying the first extinct vascular plant group solely from the fossil record.

While the term seed fern or pteridosperm remains in common use, modern science views the group differently. Rather than a single lineage, pteridosperms are now considered a paraphyletic grade-group, a collection of unrelated seed plants that are not angiosperms, conifers, ginkgos, cycads, or gnetophytes. This classification serves as a useful curatorial shorthand for extinct plants with fern-like fronds, even though these groups are spread across various clades. One potential unifying feature is the presence of ovules borne in a cupule, though this remains unconfirmed for many groups.

The historical significance of these plants was so profound that the Carboniferous Period, once dubbed the Age of Ferns, was re-evaluated as the Age of Pteridosperms. These plants flourished during the Carboniferous and Permian periods before declining in the Mesozoic Era. While most disappeared by the end of the Cretaceous, some evidence suggests they may have persisted into the Eocene. Today, the study of these plants remains complex; a 2009 study noted that our current phylogenetic analysis techniques have actually outpaced the hard data required to definitively map their evolutionary relationships.

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