> When competing for resources, killing your neighbour frees up resources, which you can take. Most species of animal and even plants do this to some extent.
If anything, I'd say plants do it more. Everything in the garden is trying to kill everything else.
Sometimes they do it in their own species, but much more commonly they do it across species. Eucalyptus will kill all but eucalyptus. Redwood trees will form networks and help each other; even an albino redwood tree (no chlorophyll https://education.nationalgeographic.org/resource/white-wond...) can survive.
A plant that killed all offshoots of itself would not survive. But plants much more often make perfect genetic copies than animals do, so the selfish gene can explain this behavior