A quote directly cited from the official wiki, the first sentence about their physiology:"The sylvari are omnivorous humanoid plants." So yes, they are plants.look at the GW2 wiki and you'll see the main difference. Besides it says BOTANICAL humanoids. Also Explorer Syllia states that the cold does not affect sylvari, but they affect plants. I'm leaning toward the thought that they are just humanoids that just RESEMBLE plants. Not that they are plants.