Pteridosperms

Pteridosperms, also known as seed ferns, are an extinct group of Paleozoic seed plants that resembled ferns in appearance but bore seeds. Their lineage spans from the Late Silurian or Early Devonian to the Permian, with the greatest diversity during the Carboniferous.

They typically had fern-like fronds with pinnate or bipinnate leaves, and reproductive structures that produced seeds enclosed in protective cupules on the fronds. Compared with true ferns, pteridosperms were seed plants, possessing vascular wood and a protective integument around the ovule, features linked to their reproductive strategy and fitness in various environments.

The best-known groups include the Medullosales, with large arborescent forms, and the Lyginopteridales. Fossils are abundant in Carboniferous coal measures of Euramerica and Gondwana, and many genera such as Lyginopteris, Medullosa, and Lagenostoma illustrate the seed-bearing habit and leafy morphology of these plants.

Pteridosperms are considered a paraphyletic assemblage rather than a natural clade, representing early experiments in seed-bearing habit that ultimately gave rise to gymnosperms. Their study helps illuminate the evolution of seeds, ovules, and secondary growth in early seed plants, and provides important context for the transition from leaf-fern-like forms to more fully woody seed plants.