Pteridospermatophyta

Pteridospermatophyta, commonly known as seed ferns, is an extinct group of seed plants that resembled ferns in appearance but produced seeds enclosed within an integument. They first appeared in the Late Devonian and persisted into the Permian, making them among the earliest seed-plant lineages and important for understanding the origin of seeds. Although their leafy habit recalls ferns, they are not true ferns.

Morphology and reproduction: Leaves (fronds) are typically large and pinnate or bipinnate. Reproductive structures included megasporangia carried on specialized leaf-like organs (megasporophylls) and, in some forms, separate microsporangia. Seeds were enclosed by integuments, forming ovules on the sporophyte. Many pteridosperms were heterosporous, producing distinct megaspores and microspores, and several lineages showed advanced vascular and woody features.

Distribution and ecology: Fossils are found worldwide, with a strong representation in Carboniferous coal-forming deposits and other Paleozoic formations. They occupied a range of habitats from swampy to upland environments and included a mix of herbaceous and woody forms. Their decline occurred as climate shifts and the diversification of true gymnosperms reduced their ecological prominence.

Taxonomy and significance: Pteridospermatophyta is an informal, historically paraphyletic grouping rather than a single natural clade. It is often treated as a stem group to seed plants or gymnosperms in modern classifications. The group is key to understanding the transition from spore-based reproduction to true seed habit, providing insight into the early evolution of ovules, seeds, and seed-plant morphology. Notable genera include Medullosa, Lepidopteris, Lyginopteris, Neuropteris, and Alethopteris.