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Sensitive Plant, Mimosa pudica

Sensitive Plant

The Sensitive plant (Mimosa pudica L.) is a creeping annual or perennial herb often grown for its curiosity value: the compound leaves fold inward and droop when touched, re-opening within minutes. Mimosa pudica is native to Brazil, but is now a pantropical weed. Other names given to this curious plant are Humble plant, Shame plant, Sleeping grass, Prayer Plant, Touch-me-not, Makahiya (Philippines), and Mori Vivi (West Indies). The Chinese name for this plant translates to "shyness grass". The species epithet, pudica, is Latinfor "bashful" or "shrinking".

The stem is erect in young plants, but becomes creeping or trailing with age. The stem is slender, branching, and sparsely to densely prickly, growing to a length of 1.5 m (5 ft). The leaves are bipinnately compound, with one or two pinnae pairs, and 10-26 leaflets per pinna. The petioles are also prickly. Pedunculate (stalked) pale pink or purpleflower heads arise from the leaf axils. The globose to ovoid heads are 8-10 mm in diameter (excluding the stamens). On close examination, it is seen that the floret petals are red in their upper part and the filaments are pink to lavender. The fruit consists of clusters of 2-8 pods from 1-2 cm long each, these prickly on the margins. The pods break into 2-5 segments and contain pale brown seeds some 2.5 mm long.

Mimosa pudica is well known for its rapid plant movement. In the evening the leaflets will fold together and the whole leaf droops downward. It then re-opens at sunrise. This type of motion has been termed nyctinastic movement. The leaves also close up under various other stimuli, such as touching, warming, or shaking. The stimulus can also be transmitted to neighbouring leaves. These types of movements have been termed seismonastic movements. The cause is a loss of turgor pressure. The movement is caused by "a rapid loss of pressure in strategically situated cells that cause the leaves to droop right before one’s eyes"

More information about the sensitive plant