In the Isle, there was formerly wide variety of plants for herbivores to eat but as of the new gamemode there is currently only one in terms of maps that is eatable by herbivores. In the future, certain herbivores will be restricted to eating certain plants found in their respective biomes.
For the Food Stats and explanations click at the link.
From Punchpacket, 22.01.2019:
We have plans for dinosaur diets to play a much bigger role in the future. What types of food that different species can eat will vary, and there will be rarer types of plants that will grant certain effects to the player when eaten. Poisoning is something that we have debated but not fully committed to.
Poisonous plants are a possibility, but we have not decided if we want to pursue those yet. For carnivores, meat will go rotten over time, and eating rotten meat will have negative effects with certain species able to stomach more than others.