|The plant itself looks rather bland, but the flowers are quite attractive.|
Mimosa pudica, also known by such names as "tickle me plant," is one of the few plants that reacts very quickly to its environment. That's right, if you poke it, it will move and you can easily see it do so. It was once thought the plant had nerves and muscles, but in fact the movement is made by a simple change in turgor pressure, which helps plants stand upright and keep their shape. However, much is yet to be discovered as to the specifics of the reaction and what exactly leads to that loss of pressure and its ability to travel to other portions of the plant.
It is native to Brazil, but grows as a weed throughout the states along the Gulf of Mexico. The scientific name basically translates to "bashful mimic" and it is thought that the movement might have evolved because drooping leaves are less attractive to herbivores.
Below is a video of this plant doing its thing:
Source is here. Image is from Wikimedia Commons under a creative commons license.