A Sensitive Plant

 

Flowers of Sensitive Plant (Mimosa pudica).
Palm Beach County, Florida. 

We usually think of movement as an animal attribute, but plants can move too.  Sure, plants move when they grow, they increase in height or diameter, but some can move rapidly in response to a stimulus.  Sensitive Plant (Mimosa pudica) is an example of a plant with this rapid movement.  Sensitive Plants are members of the pea family, the Fabaceae, and they range through the American tropics and Caribbean islands. They also grow in the Southeastern United States, Africa and Europe.  In the Southeast, Sensitive Plants flower in summer and produce a spherical inflorescence of pink flowers. 

The scientific name of Senstivie Plant, Mimosa pudica reflects its active nature.  Mimosa is from the Greek meaning mime, because the plant mimics the movement of animals. Pudica is from the Latin meaning shy. Another common name for Sensitive Plant is Shame Plant.  The shy and shame in these common names come from the plants ability to quickly close their leaves when touched, as if they want to shrink from sight.  

Compound leaves of Sensitive Plant.
Palm Beach County, Florida.

The leaflets in the center of the photo are 
closing after being touched.
Palm Beach County, Florida. 

Sensitive Plants have compound leaves with many leaflets. Each leaflet has a structure at its base called a pulvinus.  When a Sensitive Plant leaflet is touched, an electrical signal, much like a nerve impulse spreads, across the leaf.  The signal causes the pulvinus cells to lose potassium ions which causes water to leave those cells.  Because of water loss, the pulvinus collapses and the leaflets quickly fold inward.  The signal spreads and a whole section of leaf folds up. 

Video of Sensitive Plant leaflets closing.

Crooked Tree Wildlife Sanctuary, Belize.

The reason for this dramatic action by Sensitive Plants is to startle herbivores and prevent consumption of the leaflets.  You can imagine a rabbit being surprised by this fast plant movement. But if a grasshopper landed on a leaf it could be thrown completely off.  In addition to movement, Sensitive Plants are protected by spines on the stems. 

These interesting weeds grow along roadsides and in sandy soils.  When you find Sensitive Plant, give it a touch and it will show its sensitivity.