Here is a specimen from the Discovery Gallery hands on fossil exhibit at the
Louisville Science Center. It is labeled as a 'Club Moss Root' but no location or time period included. I do not know much about fossilized plants but most of the fossils I have seen are from the Mississippian or Pennsylvanian periods (Carboniferous).
Research at this
site about club mosses they were known as lycophytes of the genus
Lycopodium (
lycos Greek for wolf and
pous Greek for foot).
I did not have a ruler but the specimen seemed to be about 15 cm long and 6 cm in diameter.