Sensitive Plant (Neptunia aquatica) is exactly like its name, sensitive to the touch and when touched its tiny leaves will contract.  Did you know that it resembles a dragonfly's wings?  When glancing at the leaflets, you'll notice they are growing on both sides of the petiole, and when touched resemble dragonfly wings. 

During the growing season the sensitive plant will grow tiny yellow flowers that are about an inch wide along the stems.  You can float this plant and it will grow spreading out over the pond.  It can also be rooted in soil at the edge of a pond where it will spread out over the pond and grow to about 5-6 inches tall.  It requires sun to part shade and is hardy zones 9-11.

There are two type of sensitive plant, the regular and the giant sensitive plant.