Fungi, flowers, fruit, and foliage (growing wild, not cultivated) are one of the corner cases - they're specifically carved out by s.4(3) of the Theft Act 1968.

Fungi, flowers, fruit, and foliage (growing wild, not cultivated) are one of the corner cases - they're specifically carved out by s.4(3) of the Theft Act 1968. There are a few others, as I said: mineral rights, wild and semi-wild animals, etc. But otherwise it's not generally complicated (at least in England and Wales). Now, you have a good case that the natural things shouldn't belong to the landowner. But English law has chosen not to agree with you (unsurprisingly given the strength of the landed interest over British history). First possession is not the rule here, it's the ownership of the land it's found on that matters.