From Ohio History Central
Seed ferns were a now extinct group of plants (gymnosperms) that reproduced by seeds. However, the seeds were unprotected by a hard covering, as are the seeds of modern angiosperm plants. Most seed ferns were small plants and important during the Late Paleozoic, but never dominant. Carbonized compressions of the leaves known as Neuropteris and Alethopteris are commonly found in shales associated with Upper Paleozoic rocks.
- Cross, A. T., Gillespie, W. H., and Taggart, R. E., 1996. "Upper Paleozoic Vascular Plants," in Fossils of Ohio, edited by R. M. Feldmann and Merrianne Hackathorn. Ohio Division of Geological Survey Bulletin 70, p. 396-479.