My friend Bob from Ohio recently sent me photos of his Hoya vitellinoides that he grew from a cutting that I personally gave him from my plant. You would hardly know that they are the same plant as they look so radically different. The top photo is my plant from a couple of years ago, and the bottom two photos are of the exact same plant grown under Bob’s conditions.
There is a lot of research that could be done on just exactly what are the differences that produce such distinctive plants from the exact same cutting. There is a movement among plant scientists currently to lump many heretofore separate species into a single species. The conditions under which a plant is grown could have a lot to do with why they originally were thought to be different species, but are in fact the same plant.