There is a creeping rootstock than can result in a patch being produced.

I'd love to have a patch of bear's breeches. I planted one (gallon sized pot) five years ago. It bloomed for the first time this summer. No sign of spreading yet.

It could be the hardier Acanthus hungaricus (balcanicus).

cecily that does not sound encouraging for the seeds I got from a friend.

I planted ancanthus mollis about 8 yrs ago and had read how aggressive it could be. The first one (far right in picture) is planted in a large plastic storage container. The one next to it might be too...so long ago I'm not sure. The one on the left just went into the soil. I don't see a lot of difference in them. I really like these as they stay green all year, haven't taken over the ribes or the (assertive) plumbago, and provide a nice backdrop. Good luck!

Or Acanthus spinosus, which is rated to zone 5. In my climate, this plant spreads aggressively if happily sited, as does A. mollis. And once planted difficult to get rid of, as any bit of the deeply growing rootstock left behind will generate a new plant.

The plant does have spines on it, if that helps an ID.

Leaves look a lot like my Blue Globe Thistle, though not as prickly.

That’s the a. spinosa that is much hardier and heat tolerant.

I have had a. mollis for years and am digging it out now. It just sulks in our southern Ohio hot and humid summers for me. Even if I water in the morning, it looks sad by the afternoon.

A mollis has a curious habit of drooping in the sun, even in my cool, temperate, moist climate. It’s not a sign of anything amiss, in my garden at least. I didn’t plant it. A bit of root got in with something else. I've dug it out now but morsels of root continue to sprout.