Plants such as Mimosa pudica are also called sensitive plants, sleepy plants, action plants, touch-me-not, Shy Plants, and shameplant. This plant belongs to the pea-legume family Fabaceae and is a creeping annual or perennial flowering plant. Shy, bashful, or shrinking is what the word pudica means. A curiosity value is often attached to it.
In response to touching or shaking, the compound leaves fold inwards and droop to defend themselves, only to reopen after a few minutes. Generally found on low-nutrient soils with little shade, this plant is not shade-tolerant. Mimosas are known for their unique ability to respond to touch, which made them an ideal plant to study plant habituation and memory. A legume fruit is produced by these plants and the flowers are small and regular.
Although Mimosa pudica originally grew in the Caribbean and South and Central America, it has become a pantropical weed, growing far beyond its original range. In Southern United States, South Asia, East Asia, Micronesia, Australia, South Africa, and West Africa, it is now a common weed. Tropical crops can be damaged by the species, particularly if they are cultivated by hand. Sugar cane, bananas, soybeans, papaya, and corn are a few of the crops commonly affected by it. Thickets that are dry may pose a fire hazard.
Rapid plant movement is a characteristic of Mimosa pudica. It undergoes a change in leaf orientation referred to as nyctinastic movement or “sleep.”. Fluffy leaves close during darkness and reopen in daylight. Young plants have an upright stem, but as they age, the stem becomes crooked or trailing. It can become floppy when it hangs low.
Growing to about 30 cm in height, the plant is a spiny subshrub. Having a slender, branching stem, prickly, sparse to dense scales, the plant grows to a height of 5 feet. Besides being stimulated mechanically or electrically, leaflets also close when touched, heated, blown, and shaken. Movements of this type have been called seismonastic movements.
A French scientist named Jean-Jacques d’Ortous de Mairan was the first to study the plant. Species Plantarum by Carl Linnaeus in 1753 is the first scholarly description of Mimosa pudica. Numerous common names have been given to this species, including sensitive plant, sleepy plant, humble plant, shameplant, and touch-me-not.
Usually, there are two or three pinnae pairs per leaf, with 12 to 26 leaflets each. A prickly texture can also be found on the petioles. Mid-summer, the plant produces pedunculate (stalked) pale pink or purple flower heads with progressively more flowers as it matures.
The Mimosa’s leaves are hypersensitive to touch, just like the trigger hairs on the Venus Fly Trap. The touch-sensing function of these parts is similar to that used for defense or nutrient maintenance tasks; they have mechanoreceptors connected to mechano-sensitive channels that, upon touch stimulation, conduct calcium ions and indirectly relative anions, triggering depolarization, the initiation of an action potential.
Plants of this type are typically grown indoors as annuals, but they can also be used as ground cover. It can also be found on many Pacific islands, as well as in some parts of South and Southeast Asia. It has been introduced to a number of other regions and is considered an invasive species in many of them. Parts of Australia consider it invasive, while Western Australia and the Northern Territory declare it a weed. There is a recommendation for control in Queensland.
In conjunction with the evolution of nitrogen-fixing bacteria, Mimosa pudica may have developed its ability to fix nitrogen. A mutualistic relationship has evolved between bacteria and plants as a result of nitrogen fixation.
The spider mite and mimosa webworm are some of the natural predators of Mimosa pudica. Leaflets are wrapped in webs by both insects, which prevents them from responsively closing. When a leaf is webbed, it becomes a brown fossilized remnant after an attack. A nutrient-poor soil with good water drainage is the best environment for Mimosa pudica to grow. A scalped and eroded subsoil may also support the growth of this plant.
Besides Singapore and Bangladesh, sleepy plants are also found in Thailand, India, Nepal, Indonesia, Taiwan, Malaysia, the Philippines, Vietnam, Cambodia, Laos, Japan, and Sri Lanka.
In addition to Uganda, Nigeria, Seychelles, Ghana, Mauritius, and East Asia, the plant has also been introduced there but is not considered invasive. This species is found in Louisiana, Florida, Hawaii, Tennessee, Virginia, Maryland, Puerto Rico, Texas, Alabama, Mississippi, North Carolina, Georgia, and the territory of Guam in the United States.
Among the toxic alkaloids in Mimosa pudica is mimosine, which has also been found to be antiproliferative and apoptotic. Antioxidant and antibacterial properties are demonstrated by Mimosa pudica. Additionally, in brine shrimp lethality tests, M. pudica has been demonstrated to be non-toxic, indicating it pudica is relatively non-toxic. It has been found that Mimosa pudica is rich in alkaloids, flavonoids, and C-glycosides, along with sterols, terebinoids, tannins, saponins, and fatty acids.
Water drops and finger touches could be distinguished by Mimosa. Also, the leaf-folding response returned when other stimuli were presented, proving that the habituated behavior was not fatigue-related.
Compared to plants that live in high light, where sunshine isn’t a problem, low light environments have fewer opportunities for photosynthesis. The Mimosa plant folds in its leaves as a defensive mechanism, but there is a trade-off since folding its leaves decreases the amount of photosynthesis it can perform during the closed period by 40%.
However, folding its leaves provides a rapid defensive mechanism against predators and external stimuli that might harm the plant.
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