Just a total guess, but maybe a young (or mini var) of Yucca gloriosa?
Sorry, don't have time to do more research right now.
http://en.wikipedia.org/wiki/Y...
Edit: Didn't see any white threads (filaments) until I looked very closely at the 4th pic, then it appears there may be some?
Also, Adam's Needle is a catch-all, common name for different types of yuccas (filamentosa, gloriosa, etc.), kind of like "Spanish Dagger."
