That’s the plant spell upgrade!! It makes them a little cheaper and you can spawn 4!
No, that the point that I bought the first plant scroll (2 plants only) 2 times.
Though, maybe I am really wrong, if spells upgrades are a bit random. Nvm it much though, should play it more.
haha, about that screenshot you posted, I did know that they do that sometimes, I just didn't think anyone would notice ;) thought I could patch it next time.