Gregory Desmond was a world renowned botanist. He had some uncommon ideas, including that plants were sentient much the same as humans or animals, it was just that they had no way to communication with us. Eventually his ideas began to take a more radical turn as he began to splice human genes with plants, specifically his genes. Whether his theories were proven right or not is up for debate, but the plant, a creeper, did gain sentience. It also killed him shortly thereafter. Since then Bloodvine has existed with a hatred of humans but with the intellect of a human.
Bloodvine usually is accompanied by controlled plants. Add appropraitely level plants to any encoutners with Bloodvine. It should be noted that Bloodvine does have the ability to dominate human beings as well as plants, thogh this is not an ability he is aware of until later in his career.