From Ohio History Central
True ferns first appeared in the Devonian but looked very different from the familiar ferns of today. True ferns reproduce by means of spores. One of the common forms in Pennsylvanian coal swamps was Psaronius, that was treelike in appearance. These plants stood as high as 30 feet with a crown of large fronds. The trunk was thick near the base because of adventitious roots that grew on the surface of the trunk to the ground. Pecopteris is a name that is applied to the pinnules on the fronds. True ferns such as Psaronius became more common in the Late Paleozoic as conditions became drier and the lycopods declined. Silicified (petrified) wood of Psaronius trunks have been found at several localities in Ohio.