Is this Arundo donax?
IMHO, no. The flower of arundo donax looks quite different (see picture below) from the one in your picture which is somewhat miscanthus-like. And more, AD stalks are more separate from each other than these.
Just my 2 cents.
I tried to find pics of the flowers on the newer variegated cultivars of A. donax, like 'Peppermint Stick' but couldn't find any. I agree this one's flowers don't look like the species, but the plant itself doesn't look like any Miscanthus I've seen.
I've asked for a better picture, including the bloom. I may be trading for a division of this plant, but since it's growing in zone 9 California, I need to ID it first, to be sure it's hardy in my zone. It's apparently a 7' plant.
I think I'll post it on the Name That Plant Forum.
Looks like Miscanthus Cosmopolitan to me.
Cosmopolitan is a reverse variegation of Miscanthus Cabaret.
Here is a link that might be useful:
g_g..that's the same conclusion the Name That Plant Forum reached. It looks like a nice plant, and I'll do my best to trade for a division of it.
Worth growing! I like the seed heads, which turn coppery red in late summer. Nice contrast with the variegated foliage. Here's a link to a pic that shows the red blooms in September-ish.
Here is a link that might be useful: Miscanthus Cosmopolitan Blooms