I worked through the keys, and this must be a form of Yucca arkansana. I've seen that species before, but never with the leaves so flattened and thin.

I dont know about this particular Yucca,
but it is amazing what modification can do to a plant, changes in appearance by particular site conditions.
Did I get it right, it grows in the shade of trees?
If so a sun loving plant would react exactly that way, growing with thin spindly stalks, long " internodes" and thin, rather soft leaves.

And do you find those keys in the internet?

Bye, Lin

Thanks, Lin. I thought that your suggestion was a good one, so just posted several links that I've found helpful for plant IDs.