The horsetail tree Calamites

This tree, in size up to 20 meters, grew in the coal-swamps of the Carboniferous, the period in which most of the coal has been formed.
Originally the name Calamites was only given to the articulated and ribbed casts of the central pith of the trunk, but now the name is also used for the entire plant.
It has yielded many kinds of fossils.

Click the parts of the tree to see photos of these fossils.
Possibilities:
rhizome, roots, stem and branches, foliage, cones.

Key for somes species of Calamites.