Bloodthirsty Vegetation is one of the 2 trophy quests for chapter 2. You can see Vincent in the Temple Quarter for information about monsters although you don’t need to see him to start this quest. Vincent will pay 400 Orens for the Coccacidium, a large Archespore.
You’ll probably come across the Coccacidium while doing the ‘A Pilgrimage‘ quest. If not you can find this Archespore in the Swamp at location (#1). It’s a tough battle so make sure you’re equipped with Swallow potions and other buffs. Take the Coccacidium Head back to Vincent in the Temple Quarter for your reward.