yucca is strong ,but i've not enjoyed processing fine leaf western yucca and the fibers are fairly coarse.(will have to try "rotting" the leaves)
gotta say , dogbane is my favorite now, strong enough for a 50# bow and if the string weakens one can simply twist in new fiber after untwining.
so you can rebuild a functional bowstring in the field. can't do that with modern string material unless you carry it with you.
I've used elm bark for a lot of tying jobs and it holds up in weather for years, but its not strong a weight as dogbane can be.
There's a type of burdock that grows here in NE thats fiberous and is tempting me to try...
no nettles here.