Himalayan blackberry (Rhubus armeniacus) is a non-native, aggressively invasive blackberry. It is native to Armenia and Iran, and it was imported to the United States in 1885 because its berries are larger and sweeter than native blackberries. It was planted for commercial blackberry production, and it quickly naturalized. It is widespread in the Pacific Northwest, particularly.
I worked in the PNW, and it’s really terrible stuff. It forms large, dense thickets that are painful to walk through. And when I say large, I mean large. Canes can be up 15 feet tall and as long as 40 feet! Canes that can be up to an inch in diameter.
Himalayan blackberry is present in Illinois, but as far as I know it hasn’t been confirmed in Wisconsin. Unfortunately, I think I found two patches of it when I was cruising a property in western Vernon County in order to prepare an MFL plan. I sent pictures of the plant to an invasive plant specialist with the DNR, and she agrees that it looks like Himalayan blackberry. We’ll make a field visit this spring after it has leafed out to confirm its identity.
One patch is located along a County highway, and the other is adjacent to and on a skid road that was used during a timber harvest 10 years ago. If I saw it in two places, it’s almost sure to be present in other forests. Keep an eye out for especially large blackberry plants with fluted stems when you are in the woods.