A young Didymochlaena truncatula. Rgds

These things are pretty hard to kill. BTW, they are rhizomatous, so there's a word for you to look up! That will tend to indicate these guys are here to stay. Again, a great native plant, superb for colonizing empty space and areas too wet for other species, but not one which will work well in a "garden". I like them and have many, both in my yard and at my tree farm up north, but that's me. Incidentally, yes, the growth under a heavy pine (or other tree type) canopy will be slowed, but never stopped. tough, tough customers-you can move them any time the ground is workable. And yes, you will see some of these rhizomes when you dig. +om

I'm going to agree with Southern Shield fern, which I've always called Maiden fern, and it's also called Southern wood fern. It forms clumps, but also spreads from runner and comes up in everything. It gets quite tall in the wild, up to 3 feet. I had it in SC, and it came up in almost all my pots and any crack in the concrete every year. Here is the UF/IFAS page on it. http://gardeningsolutions.ifas.ufl.edu/plants/ornamentals/southern-shield-fern.html the spores look the same too, according to this site and picture https://www.wildflower.org/gallery/result.php?id_image=44417

Cinnamon fern? The upright part should be a reddish brown, though.