Lepidodendron is an extinct lycopod tree that lived in the great coal-age forests before the time of the dinosaurs.  The were unlike any tree that lives today, in that they did not have a heavy woody trunk.  Their bark was covered with diamond-shaped leave scares, they reproduced with a cone like structure, and they had shallow roots that grew straight out from the tree. These roots had small rootlets that left scars on the roots.  If you looked at the root in cross section you can also see the small vascular bundle that conducted water up to the leaves and food from the leaves down to the trunk.  Lepidodendron lived during the Carboniferous period.

The lycopod plants that survive today, shown as the small plant left of central in the diagram, are small herbaceous forms that live in the shade of more advance trees.

Lepidodendron root showing the root scars. From the Carboniferous in Indiana.

The vascular bundle of the root shown above.