Until some of these systematic issues discussed above are better resolved, we will give a few examples as an overview of early fern representatives. Rhacophyton is well known from the Late Devonian of North America, Europe and western Siberia. It was characterized by a semi-erect axis with rows of paired branches. Although the biseriate branches look much like the fronds of modern ferns they are not.
Fronds are, strictly speaking, elaborate compound leaves, attached to the stem by a petiole.
The frond-like structures of Rhacophyton are clearly branches with secondary xylem. The discovery of secondary xylem in the frond-like structures of Rhacophyton illustrate the taxonomic dilemma posed by this plant. If you saw it growing today, you probably wouldn't recognize it as a fern. However, its stele morphology is like many other things that we recognize as ferns. Elaborate three-dimensional branching systems are well on their way to becoming fronds, with their vascular strands distinctly different from that of the rhizome.