There are small opuntias that grow in southern, western Michigan on
sandy areas near Lake Michigan. When I lived there I saw several that
a friend had collected and was growing in pots. Opuntia doesn't
necessarily mean large prickly pear cactus. I was exploring in South
Dakota and saw many small opuntias growing on a rocky hillside.
Mentioned it to a native who lived in the area. He swore that was
impossible. Finally had to take him to the site to prove it.
[NAFEX] opuntia in Michigan,
Ernest Plutko, 02/26/2011