But the main difference is that the Pennsylvania Clubmoss branches with leaves feel round when held, but the Flat-Branched Ground Pine branches feel flat. This is due to the fact that the Pennsylvania Clubmoss leaves are all the same size and spread the same amount while the Flat-Branched Ground Pine has leaves on the bottom that are much smaller and not spreading (which gives it a flat feel). Compare the second picture on the right of a Pennsylvania Clubmoss branch with the very last picture on the bottom left which is a labeled picture of a Flat-Branched Ground Pine branch.
