ISGS - Fossil Mire Forest

The calamites, or "giant horsetails" were a group of spore producing plants very closely related to modern "horsetails" (also known as "scouring rushes"), of the genus Equisetum. Much larger than modern horsetails, this ancient group also could produce wood. Trees could reach considerable heights, although those at Riola probably did not exceed 30 feet (10 m) in height, based on the sizes of the stems observed. The trunks had a hollow center that could be filled with mud after the tree died, leaving a so-called "pith cast", which is one of the most common remains of these plants.

The calamites, like the modern horsetails, had "node-internode" architecture. All the leaves and branches were arranged in whorls borne at "nodes". These nodes can be seen in the fossils as lines that extend around the stem.

Description	Image (click for full size)
*Calamites* pith cast. Note the nodes (lines around the stem) where leaves and leaf-bearing branches would have been attached. The bottom picture illustrates a long trunk segment that is thin throughout the preserved length.
*Asterophyllities equisetiformis*. Leafy branches of a calamite tree. Note how the leaves themselves (which are thin and elongate) are arranged in whorls on the stems.
*Calamostachys*, the spore-producing cone of a calamite tree. Note again, the whorled arrangement of the appendages.
*Calamite* cones mixed with tree-fern stems or frond axes. The triangular object in the lower right of the photograph is broken piece from a "female" cone of a giant.