Mushrooms are taxonomically clearly distinct from plants and animals (and other kingdoms), but in "cuisine taxonomy" they are typically included in plants. The word "vegetables" in a restaurant's menu can well include mushrooms — no matter how much I personally dislike this inclusion.
I would like to know whether the Romans saw mushrooms as plants or vegetables. Are there passages in Roman literature that discuss or hint at the inclusion or exclusion of mushrooms within plants? Any mention like "mushrooms and plants", "mushrooms and other plants", or "mushrooms are plants" would be interesting. Any word for "mushroom" or "plant" is possible, for example boletus and holus. The context can be food or taxonomy. I did not manage to find anything. (I purposely decided to leave the question broad, since I fear there is not much relevant extant material.)