How to recognise them

The roots can be as thick as your arm with regular spaced pits. 

Fossil Info

These fossils are actually the roots of Lepidodendron. They are often preserved "in the round" in three-dimensions and have a distinctive pattern of regularly spaced dimples on the surface. They are often as thick as a human arm. The roots of Lepidodendron were very shallow and spread mostly horizontally. Their structure is quite different to the roots of trees today and so some palaeontologists think that they might be modified leaves rather than true roots with root hairs. The shallow rooting system may have contributed to the toppling of Lepidodendron trees during storms. 

Fun Fact

For many years Stigmaria and Lepidodendron were thought to be different fossil plants, but are just different parts of the one tree.

Photo: Stigmaria - photo by Verisimilus T - CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6741052