Mimosa pudica (from Latin: pudica "shy, bashful or shrinking"; also called sensitive plant, sleepy plant, action plant, touch-me-not, shame plant) is a creeping annual or perennial flowering plant of the pea/legume family Fabaceae and Magnoliopsida taxon, often grown for its curiosity value: the compound leaves fold inward and droop when touched or shaken, defending themselves from harm, and re-open a few minutes later. In the UK it has gained the Royal Horticultural Society's Award of Garden Merit.
The species is native to South and Central America, but is now a pantropical weed, and can be found in Southern United States, South Asia, East Asia and South Africa as well. It is not shade tolerant, and is primarily found on soils with low nutrient concentrations Mimosa pudica is well known for its rapid plant movement. Like a number of other plant species, it undergoes changes in leaf orientation termed "sleep" or nyctinastic movement. The foliage closes during darkness and reopens in light. This was first studied by the French scientist Jean-Jacques d'Ortous de Mairan. Due to Mimosa's unique response to touch, it became an ideal plant for many experiments regarding plant habituation and memory.
The stem is erect in young plants but becomes creeping or trailing with age. It can hang very low and become floppy. 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 purple flower heads arise from the leaf axils in mid-summer with more and more flowers as the plant gets older. The globose to ovoid heads are 8–10 mm (0.3–0.4 in) 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. Pollens are circular with approximately 8 microns diameter.
The fruit consists of clusters of two to eight pods from 1–2 cm (0.4–0.8 in) long each, these being prickly on the margins. The pods break into two to five segments and contain pale brown seeds about 2.5 mm (0.1 in) long. The flowers are insect-pollinated and wind-pollinated. The seeds have hard seed coats which restrict germination and make osmotic pressure and soil acidity less significant hindrances. High temperatures are the main stimuli that cause the seeds to end dormancy.
The roots of Mimosa pudica create carbon disulfide, which prevents certain pathogenic and mycorrhizal fungi from growing within the plant's rhizosphere. This allows the formation of nodules on the roots of the plant that contain endosymbiotic diazotrophs, which fix atmospheric nitrogen and convert it into a form that is usable by the plant.... See more
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