My guess would be that it started out as the common ‘Beacon Silver’ but has reverted to a wilder form with wider green margins. That’s what happened here. I rip large amounts out every spring and again in summer to keep it confined to one area. I’ve been doing that for years now and it hasn’t spread beyond the area where it reaches by foliage growth i.e. It doesn’t seem to seed around. Since it is growing in a very dry area with root competition from a large cedar clump and some other trees and shrubs, I don’t mind it being there as the ripping out is fairly easy and not much else will grow there.

Thank you!