If you think about it, there are basically an infinite number of shapes that could occur. For instance, a chicken could have 8 legs, or people could have square heads (maybe some of us do ;-)), but it seems that of all of the possible combinations, just a few are actually realized, which brings me to the question:
Flowers could grow in infinite ways, but in actuality, there are only three shapes that the growing tips of flowers take on. What are they? Each type of flowering is a single word.