Ground pine. Nice big patch I'd somehow overlooked. This is common in Pennsylvania as a whole, but I've never seen it just over the line in the Delaware Piedmont; it doesn't do well where there are earthworms. (Very common on the Coastal Plain, though.)
In sphagnum bog
Leaves in horizontal plane. ..one side with much shorter leaves.
Growing on the beech forest floor.
The Lycopodiaceae (class Lycopodiopsida, order Lycopodiales) are a family of primitive nonvascular plants, including all of the core clubmosses. These plants bear spores on specialized structures at the apex of a shoot; they resemble a tiny battle club, from which the common name derives. They are non-flowering and do not produce seeds.