You wouldn’t call seaweed vegan. Seaweed is seaweed all by itself. It’s a plant.
You wouldn’t call tomatoes or blueberries or nuts vegan. They’re plants.
RECIPES are vegan or not vegan, animal-free or animal-based.
If the recipe contains no animal products, it’s vegan or animal-free. If the recipe contains some part of the animal, then the recipe is animal-based.
If it’s all plants, then it’s vegan, animal-free or plant-based, etc.
Even if it’s part animal and mostly plants, it’s still considered, as a whole, an animal-based recipe.
The steamed peas I had this morning were not vegan, because I didn’t do anything to them, besides steam them. If I had put oil and garlic on them, then they were prepared animal-free or vegan style, meaning usually no butter or animal product or flavoring in the sauce or cooking substances or toppings were used to prepare the peas for the plate.
Blueberries by themselves are plants. Blueberry pie is either vegan or not vegan, animal-free or not animal-free judging by the ingredients put into the pie crust and the filling.
The point being made here is that vegetables, nuts, fruits, grains, legumes etc. are plants until such time you alter them by making a formula or recipe with them, and then the formula or the recipe made with the blueberries either contains animal products or contains no animal products.