Viola (odorata or tricolor)

[Bernd]

Not dumb at all and more a question of phytochemistry than taxonomy.
If 2 similar looking plants have a similar effect (or at least no detrimental one), there's no point in distinguishing them. Think about mushroom hunting. If there's a highly similar deadly poisonous one, you gotta learn how to avoid it. If similar species look and taste similar, who cares?

I'm not aware of differences in biochemistry between V. arvensis and tricolor, arvensis is sometimes treated as a subspecies of tricolor The whole thing is an extremely difficult species complex. So honestly I have no idea. I'm not a pharmacologist. But both were used in folk medicine so I don't believe there was much of a distinction.

Another interesting aspect to keep in mind I have previously talked about is the general role of illustrations in herbals. Most of the lavishly illustrated books that survived until this day were produced as luxury items for nobility, not as handbooks for physicians - who could never afford something like this. Poor man's herbals were likely unillustrated, as was the original Dioscorides. One simple reason was because the physicians that prescribed drugs did not go out and collect the ingredients. This was seen as an inferior job - mostly for women. Those were the ones who held the botanical knowledge of local plants. But were not necessarily literate. So there was a gap between the audience of herbals and the people who collected the plants. Hence the quality and accuracy of illustrations was not a top priority.