Yes, just a place holder. If you are not up to level IV on a bonus, those will be in the bonus round. Once you get to level IV, then the next one you need will pop in. If you do not need but one, then the flowers fill in the spaces.
Sometimes, there are only a few, short groups of a bonus and the rest are flowers so you cannot make a long chain for one of your turns. When that happens, I make a super long chain of the flowers to get them out of the way and then it usually fills in so I can make longer chains of the bonus icons.