8.5" Carboniferous Fossil Fern and Horsetail Plate - Two Species

Pecopteris is a form classification (taxa) for the leaves of a fern associated with the tree fern Psaronius. It is one of the most common Pennsylvanian age plants and grew up to ten meters (30 feet) tall and produced about 7,000 spores per leaf.

Annularia is the form genus of leaf clusters of tree-like sphenophytes (horsetails) known as Calamites.

Leaves on Calamites trees formed in clusters of 8 or more, called whorls, at spaced nodes along stems. Annularia indicate flat, starburst-shaped whorls, but the shapes of the leaves themselves could vary from oval (A. sphenophylloides) to lanceolate or needle-like (A. radiata). They can also be identified by midline veins throughout the leaf from node to leaf tip.

We use these terms to describe the shapes of fossil imprints. Exact species are often difficult to determine, but these form taxa help to distinguish the prolific species of sphenophytes that defined the Carboniferous Period.