Here's a good debate point. Let's consider this scenario:
1. A plant of Crassula multicava is planted for decoration in a part of the nursery.
2. Over later years, several new plants start sprouting elsewhere in the vicinity.
3. The plant is now fairly established (10-20 plants), but many still "inside the fence".
This is proof of naturalization, although locally. I guess this is a grey area for many people, but how do you take examples such as this? Does something have to be encroaching into native or wild habitat to count? Does it have to "jump the fence" in significant numbers, or does only one need to lie outside?
How are we to judge in what circumstances jumping the fence matters (for instance if the plant is very close,or very far from the fence respectively creates scenarios that are not equal in consideration).