Variable Milfoil (Myriophyllum heterophyllum) has flowers that are tiny, obscure features of the plant. Flowers appear on an emergent stem to lift them out of the water for pollination, and they are two times smaller than the bract (specialized leaves associated with reproductive structures) that supports them. Everything else about this plant is so showy and in your face, but one has to really get down and personal to see the miniature flowers. This is what I got:
