Seed ferns included vinelike plants in the undergrowth and trees such as Medullosa. Some tree genera were very tall, with trunks more than two feet in diameter. Unlike the true ferns, still living today, seed ferns declined steadily after the close of the Pennsylvanian Period and finally became extinct during Jurassic time. During Pennsylvanian time, however, they were much more numerous and varied than true ferns.
Venation of seed fern leaflets
Alethopteris Odontopteris Mariopteris Neuropteris Linopteris
Most of the common seed ferns found as fossils in Illinois can be referred to the following leaf genera: Alethopteris, Neuropteris, Odontopteris, Linopteris, Mariopteris (which may be a true fern), Cyclopteris, and Spiropteris. Cyclopteris includes circular leaves that occurred at the base of leaves referable to Neuropteris. Spiropteris includes young leaves that had not yet uncoiled and may belong to either true ferns or seed ferns.
CORDAITES
(Plates [1] and [2])
Reconstruction of Cordaites
(after Hirmer)
Cordaitean trees, forerunners of modern conifers such as pine and spruce, were important during the Pennsylvanian Period for they were distributed throughout the world. These trees, among the tallest plants of the time, sometimes grew more than 100 feet high.
The cordaitean trunk was unbranched for three-fourths of the height of the tree and was topped by dense branches bearing large, simple, straplike leaves spirally arranged. The leaves had closely set parallel veins and measured from half an inch to three feet or more long.