Well, Violets, for obvious reason but also forget-me-not , thistle and night-queen.
Edit : ok so I saw everyone kinda explaining their choice in the reaction and now I want to do the same (even if I don’t know if you’ll see that edit) : so we all know that I thought of Violets because of the name, but I thought of forget me not because they’re little flower that has that vibe of a quiet kid that is reading in the background, which was the type of guy Vio was in the volume 1 of the manga (if I remember which events happens where in the tomes right).
I thought of thistle because at first glance all you gonna see is the spikes. You may even think of it as a weed and not as a flower. But if you study it closer you’ll see that the spikes are only 1 part of it and the rest are all soft. It’s a beautiful flower in my mind, plus it can grow in arid soil !
As for the Night-Queens well it’s because they bloom at night and close by morning that’s all XD. I just thought it was fitting :) (plus by googling it to make sure that I had the right name I saw one that was purple, could be an edit but still !!)