It’s not, though. There is a perfectly viable market of seeds and such for non-biolumenescent plants. You can, in fact, plant watermelon seeds and use the seeds in the resulting watermelon to plant more watermelon plants. Crazy.
I don’t understand what you’re trying to argue, but the patent laws aren’t designed to patent generic, pre-existing plants like generic watermelon.
This is not a natural plant though.