Reconstruction of Megaphyton
(after Hirmer)
Because fossils of complete fern plants have not yet been found, separate names have been adopted for detached leaves, stems, and other parts. For example, the fossil stems of some Pennsylvanian ferns found in Illinois have been referred to two genera, Megaphyton, whose leaf attachment scars are arranged in two vertical rows, one on either side of the stem, and Caulopteris, whose leaf scars are arranged in a steep spiral that becomes progressively flatter upward until near the top they appear to be whorled. When the stem is a petrifaction, with internal structures preserved, it is called Psaronius. The fronds are referred to a number of genera, but those most commonly found in Illinois are Pecopteris, Asterotheca, and Ptychocarpus.
Venation of seed fern leaflets
Pecopteris Asterotheca Ptychocarpus
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