Why do blackberry plants grow vines with 3 leaves and sometimes with 5?

Question

Why do blackberry plants grow vines with 3 leaves and sometimes with 5?

Answer 1

Every plants will have some instances of 3 and 5 leaflets. This is the nature of the species. As the plant matures, you will see many more with 5 leaflets, but you should still see a good mix.

Of course, this can depend on cultivar as well. Some may not be bred to be as dense, or a broadleaved.