Early last year, I planted several thornless blackberry plants. This year there have been a few berries so far, but there are some new vines. The ones I planted mostly have leaflets in groups of three, but the new vines have groups of five leaflets. Other than that they look the same. I'm wondering, are these new vines really the same plant??
Thornless Blackberry Plants
Certified GKH Gardening Expert
Thornless blackberries can have either 3 or 5 leaves in a group so it could be the same plant and likely is. There is an outside chance that you are seeing the plant revert, but until you see some other difference, such as in the fruit or the canes, I would not worry about it.