Re: Narrow leaf Yucca flaccida form (like a Yucca rostrata)
Thanks for showing us your find, it's a very form.
You must try to dug up a rhizome and grow it in your garden, so you can see if it's genetically or growing conditions which is the reason to the very narrow leaves.
It would be great with such narrow leaf flaccida, genes when breeding hybrids with narrow leaves.
The soil in which this plant grows is also very interesting, very sandy soil for a forest, was it near a stream, so that the humus were washed away annually?
Btw. Both Yucca 'Golden Sword' and 'Bright Edge' has leaves up to almost 3 cm in width, but very similar in growth.