SEED FERNS (Plate 4)

SEED FERNS (Plate 4)

Seed ferns resembled true ferns in general, but they produced seeds, borne on modified leaves. Where spore sacs and seeds are absent, the leaves of seed ferns are difficult to distinguish from those of spore ferns, although individual seed fern leaflets, called pinnae, are somewhat larger.

Medullosa Reconstruction and original drawing by Wilson N. Stewart

Seed ferns included vinelike plants in the undergrowth and trees such as Medullosa. Some tree genera were very tall, 16 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.