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).
I've struggled with this argument before. If you plant something in your garden and it sets seed resulting in new plants 100ft outside your garden - and these new plants successfully grow and set their own seed then that's tickable to most, right? But what if you have a massive garden and that 100ft is still inside the garden boundaries. No fences have been 'hopped' yet the mechanism and distance are identical in both scenarios. Not many folks would tick it would they? The plants have no concept of the fence, so what's the difference? Pure craziness.
It's like creeping around the outside of the Abbey Gardens on Tresco, Scilly. Anything on one side of the wall is fine, but if it's on the inside edge....oh dear me no. Even if both sides of the wall are already a long way from the parent plants. And what to do if it's growing on top of the wall...aaaarrggghhh, run! Pretend you didn't see it! :)
Personally speaking I haven't ticked any vascular plants from inside a garden although ticking bryophytes in a garden (and inverts, fungi, lichens, any verts that aren't pets etc) is perfectly fine. I have seen plenty of wild plants (native and introduced) inside of gardens, but none were ticks at the time so it's a dilemna I haven't had to lose sleep over. Crassula multicava is doing rather too well for itself on many drystone walls on Tresco and, more recently, St Marys on Scilly. If you are determined to have "good" plants of it on your list then that's where you need to look. Scilly is AMAZING for ridiculous plants gone wild.
Thank you for your advice and for sharing your experience, this is the best site I've ever met 192.168.l.254