"A Man-eating Water Lily" 

Unless the plants already became like the dead pumpkin king before or other mutant plants which became leaders of the other mutant plants….

It was not easy to find such intelligent mutant plants. 

Even the tree roots that grabbed the worm's carcass were not so intelligent and just acted on instinct to devour carcasses. 

That tree didn't target Ainsley not because it was a kind one but because it only ate carcasses and not fresh, living things. 

Other mutant plants would be 'offended' if someone or something attacked them, but most of the responses were also more like a reflex than a show of intelligence. 

The Sun Tree might be a slightly intelligent mutant plant that could initiate cooperation with the Sun-Eater. 

The tree needed something and the Sun-eater would help. In exchange, the Sun Tree gave the Sunlight Fruit to the Sun-eater.