Corystosperms

Corystosperms are an extinct group of seed plants known from fossil records dating to the late Paleozoic and early Mesozoic. They are not a single, clearly defined modern lineage but rather an informal assemblage of taxa that paleobotanists have grouped together because of shared reproductive and leaf-related features. Their exact evolutionary relationships among other early gymnosperms remain uncertain, and they are often treated as a paraphyletic or stem group within early seed plants.

Morphology and reproduction within corystosperms varied, but they typically possessed woody stems and leaves that ranged from simple to pinnate forms. Reproductive structures involved ovules borne in cupule-like coverings, sometimes arranged along axes or close to leaf bases. These cupulate or cupule-bearing organs enclosed the seeds, representing an early strategy for protecting and dispersing seeds in terrestrial environments. The leaf and stem anatomy of corystosperms indicates adaptation to mixed to drier Paleozoic climates, though precise ecological preferences likely varied among genera.

Fossil evidence of corystosperms has been found in various Permian and, less commonly, Triassic sediments around the world, with notable representations in Gondwanan and Laurasian assemblages. Their fossils contribute to understanding the early diversification of gymnosperms and the evolution of seed-bearing structures after the Carboniferous period. While not a living group, corystosperms provide insight into the morphology and ecology of early seed plants and their role in late Paleozoic terrestrial ecosystems.