I found this at the top of a creek bank in a dense oak-pine forest in east central Alabama, zone 8a.
As you can see in the pics, its single leaf is dissected, resembling a fern frond. It is lighter green near the central veins. Unlike a fern, the leaf and petiole are herbaceous.
There are no spore sites on the underside, of course.
There is an older stem attached, perhaps of last year's leaf or possibly a bloom or spathe.
It has a short rhizome with radiating tuberous roots with little branching.
The rhizome is somewhat fragile; part of it broke off as I was digging it up. I held the pieces together for the photo of the roots. I included the broken piece in the fourth picture, showing the underside of the leaf.
It was growing in a deep layer of decomposing leaves in early December.
I potted it in a similar medium (with the broken rhizome to one side, in the hope that it will produce another plant) and put it in a shady spot. A month later, it looks unchanged.
The rhizome and roots and the solitary leaf remind me of Jack-in-the-pulpit (Arisaema). Colonies of Jack-in-the-pulpit grow nearby in the same material, but they are dormant now. Perhaps it is an estivating relative that grows in the winter and is dormant in summer, like Arum italicum.
JasperDale wrote:Any chance it could be Rumohra adiantifolius aka common Leatherleaf Fern that florists use ?
Unlikely as Rumohra adiantifolius is not found north of Florida according to PLANTS.
Botrychium spp. however are rather common in much of the SE US.
There is a close resemblance because they're related (Polypodiaceae family).