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I came across this video on Facebook where a plant closes its leaves when touched. Unfortunately the video does not mention the name of this plant.
What's the name of this plant, and where can I see it?
It is a Mimosa pudica, a wonderful plant. According to wikipedia you can find it in the following places:
Mimosa pudica is native to South America and Central America. It has been introduced to many other regions and is regarded as an invasive species in Tanzania, South Asia and South East Asia and many Pacific Islands. It is regarded as invasive in parts of Australia and is a declared weed in the Northern Territory, and Western Australia although not naturalized there. Control is recommended in Queensland. It has also been introduced to Nigeria, Seychelles, Mauritius and East Asia but is not regarded as invasive in those places. In the United States of America, it grows in Florida, Hawaii, Virginia, Maryland, Puerto Rico, Texas, and the Virgin Islands.
If you think that's impressive, look at this video of Dionaea muscipula the venus fly trap:
Why do mimosa plants close when touched?
The mimosa pudica is a sensitive old soul, and it likely evolved its touch-me-not traits to put off herbivores.
Asked by: Harriet Best, China
The leaves of the ‘touch-me-not’ fold up and droop each evening before reopening at dawn. They also do this more rapidly if they are touched or shaken. It is likely the responses evolved separately. Many plants close up at night, usually to protect pollen or reduce water loss while the leaves aren’t photosynthesising.
But the Mimosa genus is a creeping shrub and highly attractive to grazing animals. It seems that at some point in its evolution a Mimosa appeared that closed up when touched. Doing so reduced the leaf area presented to herbivores and made the plant look wilted. If this was enough to make grazers look for another plant, then the genes for touch sensitivity would have spread, eventually leading to a new species.
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Do They Have Medicinal Uses?
The plants are said to have some medicinal uses despite the fact that they have some toxicity and so they are not edible for consumption. The leaves, flowers and roots have medicinal uses, especially for treatments related to skin and inflammations. The home treatments for inflammations and several skin problems include the grinding of leaves, flowers and the roots to a paste and applying it on the affected area. The plant is also said to be effective against cobra venom and also the headaches from migraines.
However, these traditional treatments are not scientifically proved and so if you want to try it out, there should be proper guidance and understanding. I have heard a lot about the medicinal use of this plant while I was growing up, but frankly, I have no experience using them even once.
The medicinal uses of mimosa pudica may be a subject with scopes for more studies.
The shrinking leaves of a mimosa pudica plant
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Why do plants close their leaves at night?
Plants move in different ways. For some it is just a &ldquoblowing in the wind way.&rdquo But for others, the movement is intentional, as in plant tendrils grabbing poles to climb on.
Another example of plant movement is nyctinasty &ndash closure of the leaves entirely.
Nyctinasty is the movement of leaves and some flowers that happens in response to changes around them.
Think of it in human terms and circadian rhythms. We sleep in response to the change of night and day but plants don&rsquot sleep. They just take a little breather from the light.
Types of nastic movement in plants
Nyctinasty is just one type of nastic movement in plants (reversible and repeatable movements in response to stimuli that is part of a plant&rsquos make-up.)
The Venus fly try eating bugs is another example of nastic movement in plants.
Plants 'talk to' each other through their roots
Plants use their roots to “listen in” on their neighbours, according to research that adds to evidence that plants have their own unique forms of communication.
The study found that plants in a crowded environment secrete chemicals into the soil that prompt their neighbours to grow more aggressively, presumably to avoid being left in the shade.
“If we have a problem with our neighbours, we can move flat,” said Velemir Ninkovic, an ecologist at the Swedish University of Agricultural Sciences in Uppsala and lead author. “Plants can’t do that. They’ve accepted that and they use signals to avoid competing situations and to prepare for future competition.”
Previously, scientists have shown that when plant leaves are touched as they brush up against the leaves and branches of neighbours they alter their growth strategies. Mature trees have been seen to experience “canopy shyness” and rein in their growth under crowded conditions. Others, take a more combative approach, diverting resources from root growth to expand more rapidly above ground.
The latest study reveals that this behaviour is driven, not just by mechanical cues picked up by leaves, but by chemical secretions in the soil.
The study, published in the journal Plos One, focussed on corn seedlings, which tend to boost growth in a stressed environment. Ninkovic and colleagues simulated the touch of a nearby plant by stroking the leaves for a minute each day using a makeup brush.
When they then removed the plant and placed a new one its growth solution they found that the new plant also diverted its resources to growing more leaves and fewer roots. Seedlings that were planted in growth solution that had previously hosted untouched plants did not show this pattern.
The possibility that plants communicate has surfaced periodically as a crackpot idea – in the 1980s it was suggested that trees send out electrical pulses, called W-waves, when their neighbours were chopped down. However, in recent years, fresh evidence has emerged that plants are constantly sending and receiving signals that scientists are now learning to eavesdrop on. As well as canopy shyness and aggression, plants warn their neighbours of impending aphid attacks via thread-like filaments of fungi that connect roots in complex communication networks and are able to detect whether they are surrounded by “strangers” or their own kin.
Movement in Plants (With Diagram)
The first two types of movements are called as vital movements because they are exhib­ited only by the living cells or organisms.
Movement Type # 1. Movements of Locomotion:
Those movements in which whole of the plant body or the cell or cytoplasm moves from one place to another are called as movements of locomotion. These movements may occur ei­ther spontaneously or in response to a certain external stimulus and are called as autonomic and paratonic (or induced) movements respectively. Paratonic movements of locomotion are also known as tactic movements.
(a) Autonomic Movements of Locomotion:
Such type of movements take place due to the presence of cilia or flagella e.g., Chlamydomonas, Volvox, flagellated bacteria, flagellated or ciliated reproduc­tive cells etc.
Such movements are exhibited by Myxomycetes where the na­ked Plasmodium moves by producing pseudopodia like an Amoeba.
In living cells of many plants the cytoplasm including various cell-organelles moves around the vacuoles. This movement of the cytoplasm is called protoplasmic stream­ing or cyclosis. It is of two types—rotation and circulation. In rotation, which is exhibited by plants like Chara, Hydrilla Vallisneria, Elodea etc., the cytoplasm moves either clockwise or anti-clockwise around a larger central vacuole. While in circulation, which is exhibited by the cell of staminal hairs of plants like Tradeschantia, the cytoplasm moves in both clockwise and anticlockwise directions around many smaller vacu­oles.
(b) Paratonic or Induced Movements of Locomotion or the Tactic Movements or Taxes:
(1) Phototactic Movements or Phototaxis:
These movements occur in response to an ex­ternal stimulus, the light and are exhibited by zoospores and gametes of certain algae e.g., Chlamydomonas, Volvox, Ulothrix, Cladophora etc. They show a positive phototactic move­ment under diffused light and a negative phototactic movement under intense light.
(2) Chemotactic Movements or chemo-taxis:
These movements occur in response to an external chemical stimulus. Such movements are exhibited most commonly by the antherozoids in bryophytes and pteridophytes where the archegonia secrete some chemical substances hav­ing a peculiar odour towards which the antherozoids are attracted chemotactically.
(3) Thermotatic Movements or thermotaxis:
Such movements result due to an external heat stimulus. For instance, if a large vessel containing some Chlamydomonas in cold water is warmed on one side, the Chlamydomonas cells will move and collect towards the warmer side (positive thermotaxis). However, a negative thermotaxis will occur if the temperature becomes too high.
Movement Type # 2. Movements of Curvature:
In higher plants which are fixed, the movements are restricted only to the bending or, curvature of some of their parts. Such movements are called as curvature movements and may be either autonomic i.e., sponta­neous or paratonic i.e., induced. The curvature movements may be of two types—variation movements and growth movements. In variation movements the cur­vature or the bending of the plant part is temporary while in growth movements it is of permanent nature.
(a) Autonomic Movements of Curvature:
(1) Autonomic movements of variation:
Tele­graph plant (Desmodium gyrans) is an excellent ex­ample of such movements. In this plant the com­pound leaf consists of a larger terminal and two smaller lateral leaflets (Fig. 21.2). During day time, the two lateral leaflets exhibit peculiar and interesting movements.
Sometime they move upward at an angle of 90° and come to lie parallel to the rachis. Again, they may move downward at 180° so that they are parallel to the rachis. They may again move upward at 90° to come in their original position. All these movements occur with jerks after intervals, each movement being completed in about 2 minutes.
(2) Autonomic Movements of Growth:
(i) Hyponastic and epinastic movements:
These movements occur in bifacial organs like young leaves, flower sepals, petals etc., and result due to the differential growth on the two sides of such organs. For instance, if there is more growth on the lower side of sepals and petals the flower will close. Such movements are called as hyponastic movements.
On the other hand, if there is more growth on their upper side the flower will open. Such movements are called as epinastic movements. Examples of these nastic movements may be found in ferns where the leaves (fronds) become circinately coiled in young condition (hyponasty) and erect in older condition (epinasty) or in the opening and closing of flowers in many plants such as Crocus.
(ii) Nutational movements:
Sometimes the growth of the stem apices occurs in a zig-zag manner. It is because the two sides of the stem apex alternatively grow more. Such growth movements are called as nutational movements and are common in those stem apices which are not strictly rounded but flattened.
(iii) Circumnutational movements:
In strictly rounded apices the growth occurs in a rota­tional way. It is because the region of maximum growth gradually passes round the growing apex. Such movements are called as circumnutational movements.
(b) Paratonic Movements of Curvature:
(1) Paratonic movements of growth or tropical movements or tropisms:
When growth move­ments occur in response to an external stimulus which is unidirectional, they are called as tropical movements and the phenomenon of such a movement is called as tropism. Depending upon the nature of the unidirectional external stimulus the tropical movements are of many types:-
(i) Geotropic movements or geotropism (gravitropism):
The tropical movements which take place in response to the gravity stimulus are called as geotropic movements and this phenomenon as geotropism. The primary roots grow down into the soil and are positively geotropic.
The secondary roots growing at rights angles to the force of gravity are called as Diageo tropic. While those growing at some intermediate angle (between 0° and 90° to the vertical) are said to be plagiogeotropic (plagiogravitropic). On the other hand, the pri­mary stems are negatively geotropic.
Geotropism in primary roots and stems can easily be demonstrated by sowing certain maize seeds in the soil so that their radicles lie in different directions. After a few days it will be noticed that irrespective of their position, the radicles in all the seeds always go down while the coleoptile always grow in upward direction (Fig 21.3).
That the geotropic curvature results due to unilateral gravity stimulus can be demonstrated by using a clinostat (Fig 21.4). If a young potted plant is fixed on a clinostat in horizontal position and rotated, neither the root will bend down nor the stem will curve upward. It is because in such case, the effect of gravity will be uniform all round the stem and root.
If however, the plant lies in horizontal position and is not rotated, the stem and the root will receive gravity stimulus only on their lower sides or the effect of gravity will be unilateral. This will results in a positive geotropic curvature in root and negative geotropic curvature in stem.
In case of roots, the gravity stimulus is perceived only by the root cap which covers the root tip. However, the geotropic curvature takes place a little behind the root tip, in the re­gion of cell elongation. The effect of the unilateral stimulus of gravity causes unequal distribution of growth hormone auxin in the root tip i.e., more auxin concentrates on the lower side than on the upper side. This in turn results in more growth on the upper side and less growth on lower side, and ultimately a positive geotropic curvature is observed (Fig. 21.5).
But, in case of stem the higher concentration of auxin on the lower side promotes more growth on that side so that a negative geotropic curvature is observed. (The root cap is a thimble-like mass of cells which covers the root tip. It consists of a central cylinder called columella in which cells are arranged in regular tiers. Columella is surrounded by one or more layers of peripheral cells. (literally, thimble means a cap-like cover with a pitted surface worn in sewing to pro­tect the end of finger that pushes the needle).
Microsurgical removal of root cap abolishes the gravitropic response of the root with­out however, interfering with its elongation or growth. Replacing the root cap or regenera­tion of root cap after an interval of time, restores the gravity response of the root. Within the root cap, the cells of columella especially the innermost ones, are sensitive to the grav­ity stimulus and not the peripheral cells of the root cap.
In the beginning of the 20th century, Nemec (1901) and Haberlandt (1902) put forward starch-statolith hypothesis independently to explain mechanism of gravitropic response by roots. According to this hypothesis, some specialized plastids called amyloplasts containing a few starch grains inside them are present in columella cells of the root cap. These amyloplasts and the columella cells, which contain these can sense gravity stimulus and have been called as statoliths and statocytes respectively.
When root tip along with its root cap is placed horizontally, the statoliths sediments under the influence of gravity stimulus on the basal sides of the statocytes and provide the basic perception mechanism for gravitropic response. The starch-statolith hypothesis has been supported by many scientists but also rejected by others and it has never received universal acceptance).
(ii) Phototropic movements or phototropism:
The tropical movements which occur in re­sponse to an external unilateral light stimulus are called as phototropic movements. These movements are commonly found in young stem tips which curve towards the unilateral light stimu­lus and thus, are called as positively phototropic.
This can be observed very easily by placing a potted plant in a room near an open window. After a few hours, the stem will be seen bending to­wards the window, the latter being the unilateral source of light (Fig. 21.6). The roots in some plants also exhibit phototropic movements but they are negatively phototropic.
When the stem tip receives uniform light all around, the concentration of the growth hormone auxin also remains uniform in the tip. But when the tip receives unilateral light, the conc. of auxin be­comes more in the shaded side than in the lighted side. Consequently, the higher conc. of auxin in the shaded side causes that side to grow more result­ing ultimately in a positive phototropic curvature (Fig. 21.7).
If however, a small young potted plant receiving unilateral light is fixed on a clinostat in a vertical position and rotated, there will be no phototropic curvature in the stem. It is because in this case the stem tip will be receiving unilateral light all around its tip and there will be no unequal distribution of the auxin.
Unilateral blue light is also known to be effective and essential in causing phototro­pic curvature.
(iii) Thigmotropic or haptotropic movements:
These movements take place in response to a touch or contact stimulus and are very common in plants which climb by tendrils (Fig. 21.8).
In such plants e.g., Passiflora, the tip of the tendril in the beginning moves freely in the air. 33ut as soon as it comes in contact with a solid object which may provide it support (i.e., it gets the contact stimulus), it twines round the object so that the plant may climb upward. The twining of the tendril around the support is due to less growth on that side of the tendril which is in contact with the support than the more growth on the free opposite side.
(iv) Hydrotropic movement or hydrotropism:
The tropical movements occurring in response to water stimulus are called as hydrotropic movements. These are commonly found in young roots and can be demonstrated by the following simple experiment: Some seeds soaked in water the previous night are kept on a wire gauze covered with saw dust. The water gauze is then kept slanting in humid condition. After a few days, the radicles will be seen bending towards the moist saw dust (Fig. 21.9).
Cheinotropic movements occur in re­sponse to some chemical stimulus and are best exhibited by fungal hyphae and pollen tubes.
(vi) Thermotropism and Aerotropism:
These tropical move­ments are not very important. When they occur in response to temperature stimulus, they are called as thermotropic movements. In case the stimulus is air, they are called as aerotropic move­ments.
(2) Paratonic movements of variation or nastic move­ments:
When growth movements occur in response to an external stimulus which is not unidirectional but diffused, they are called as nastic movements. These movements occur only in bifacial structures like leaves, sepals, petals etc., and may be of many types:
(i) Nyctinastic movements (or sleep movements):
In many plants the leaves and flowers ac­quire a particular but different position during day and at night. Such movements are called as nyctinastic movements or sleep movements. If these movements result in response to the presence or absence of light, they are called as photonastic movements e.g., Oxalis sp. (Fig. 21.10) where the flowers and leaves open in the morning and close at night. In other plants such as Crocus and Tulip the flowers open at higher temperatures. Such movements which occur in response to tem­perature stimulus are called as thermonastic movements.
(ii) Seismonastic movements:
These movements are best exhibited by sensitive plant (Mimosa pudica) and occur in response to a touch or shock stimulus including shaking or wind, falling of rain drops, wounding by cutting and intense heating or burning.
In this plant the leaves are bipinnately compound with a swollen pulvinus at the bases of each leaf and similar but smaller pulvinules at the bases of each leaflet or pinna. If a terminal pinnule of a leaflet is touched or given a shock treatment, the stimulus passes downward to the pulvinule and all the pinnules of that leaflet get successively closed in pairs. Now the stimulus passes to the other pinnae or leaflets so that their pinnules also close down and finally it reaches the pulvinus resulting in drooping of whole of the leaf (Fig. 21.11 A, B). Whole of this process is completed just in few seconds.
The pulvinus contains a number of specialised large thin walled parenchymatous cells called motor cells which undergo reversible changes in turgor in response to the stimulus. When stimulus reaches the pulvinus, the osmotic pressure of motor cells is decreased. Consequently, water is released from them into intercellular spaces and they suddenly collapse resulting in drooping down of the leaflets and the leaf.
After the lapse of sometime, the leaf recovers from the shock or touch stimulus, the turgor of motor cells is restored and the leaflets and the leaf come in their normal erect position (see, Fig. 21.11 A & C). It is now well established that almost any part of Mimosa plant can perceive the stimulus and transmits it to the pulvinus as electric pulses through phloem sieve tubes at velocities up to 2 cm s -1 . The appearance of the action potential is correlated with rapid uptake of protons (H + ).
When action potential reaches the pulvinus, it stimulates rapid efflux of both K + and sugars from motor cells into the apoplast (cell walls and intercellular spaces) decreasing their osmotic pressure. Consequently, water is released from the motor cells, which now be­come flaccid due to loss of turgor and collapse resulting in drooping down of the leaf. After sometime, reverse changes occur to restore the turgor of motor cells and the leaf comes in its original straight position again.
Some scientists especially Hermann Schildknetcht (1983, 1984), have found certain chemical substances isolated from phloem sap of Mimosa pudica and Acacia Karroo (the latter plant is not senstive to touch but exhibits nyctinasty) which activate pulvini in these plants when applied to cut end of the stem. These chemical substances have been called as turgorins by Schildknetcht and are identified as β-D-glucosides of gallic acid. Chemical structure of one of the most active turgorins (previously known as periodic leaf movement factors (PLMFs) is given in Fig. 21.12.
It is believed that turgorins may give rise to action potential in a manner similar to the neurotransmitter acetylcholine in animals but at a much lower velocity (Action potential trav­els along the animal nerve cells at velocities of tens of meters per second plants do not have nerve tissues and the action potential may travel only upto 2 cm s -1 ). In both the cases (plants and animals), action potentials are caused by flexes of specific ions across the cell membranes.
(Turgorins are so named because they act on turgor of pulvini. These have been isolated from over a dozen higher plants which exhibit nyctinastic movements and are believed to be hormones that control nastic movements).
(iii) Thigmonastic or haptonastic movements:
The movements are found in the leaves of Drosera (Sundew) and Dionaea (Venus Fly Trap) and result in response to the touch stimulus of the insects. In Drosera, as soon as an insect sits on the leaf, the tentacles curve inward to trap the insect. Similarly in Dionaea, the two halves of the leaf curve upward along the mid­rib. These parts of the leaves come to their normal position after the insect has been digested.
Movement Type # 3. Hygroscopic Movements:
These movements are found only in dead parts of the plants which are hygroscopic in nature and result either due to loss or gain of water by them from the atmosphere. Hygroscopic movements can best be observed in the elaters in bryophytes, peristome teeth in moss capsules, elaters of Equisetum spores etc.
Plants with Weird Leaves: Leaves That Move
From time to time, I like to write an article about the oddness of some leaves. Here’s yet another, about plants whose leaves actually move.
Leaves Move All the Time
The truth is, leaves that move are not that unusual. They notably move in the wind, or when touched by rain drops or brushed against. However, there are extraneous movements: the plant isn’t moving on its own, it is being moved. That said, many plants do have leaves that move themselves. You’ll learn more about them by reading the following text.
Movement for Protection
Resurrection fern (Pleopeltis polypodioides) fronds curl up and look dead when dry, but will green up again when the rains come. Source: apalacheehills.com
Many plants have leaves that curl up or roll down under stressful conditions—drought or cold, for example—but recover afterward. The resurrection fern (Pleopeltis polypodioides, syn. Polypodium polypodioides) can survive without a drop of water for many months, even years, then its apparently dead fronds become completely green and functional within 24 hours after a good soaking. Two other resurrection plants are the rose of Jericho (Selaginella lepidophylla) and the alpine gesneriad ramonda (Ramonda spp.).
These drooping winter rhododendron leaves will straighten up, uncurl and come back to life when warmer weather arrives. Source: http://www.indefenseofplants.com
As for movement to improve cold resistance, the thick leaves of many hardy rhododendrons (Rhododendron spp.) lose most of their moisture and both curl and hang limply all winter, giving their owners quite a scare, yet recover fully when spring returns. It’s thought this habit helps keep frost crystals from forming and damaging leaf cells.
Turning Towards the Sun
Unless turned regularly, most houseplants will bend in the direction of the light source, Source: Donnie, http://www.houzz.com
On most plants, leaves will turn to face the direction of the sun, at least to some degree. If you transplant or otherwise move a plant—or even if you just cut an overhanging branch that was blocking the sun!—the leaf will adjust, changing its position, usually quite slowly, over days or weeks. This is particularly easy to observe on a forest edge where most light comes from the side or on a windowsill in your home if you don’t give your houseplants the traditional quarter turn regularly: most of the leaves will clearly orient towards the light. This habit of growing towards the source of light is called phototropism. (Remember that term from school?)
Prayer plant (Maranta leuconeura) leaves move upward at night, like hands in prayer. Source: Aida F., http://www.pinterest.
Other plants have the curious habits of folding their leaves at night, either upward or downward, a phenomenon called nyctinasty. It’s actually very common in some plant families, such as the legume family (Fabaceae) and the oxalis family (Oxalidaceae). You may have noticed this in clover (Trifolium) or false shamrock (Oxalis triangularis), but the best-known nyctinastic plant is the popular houseplant known as the prayer plant (Maranta leuconeura), whose leaves fold up at night like hands in prayer.
This kind of movement is caused by a hinge-like structure at the base of the leaf or leaflet called the pulvinus (plural: pulvini) that is filled with water during the day, but drains at night, so that the resulting lack of turgor causes the leaf to fold.
Scientists still debate why plants do this.
Plants That Dance
Carefully watch the fire fern (Oxalis hedysaroides ‘Rubra’)—not this photo but a real plant!—and you’ll discover it’s in nearly constant movement. Source: bluepumilio.com
There are plants that, under the appropriate conditions, take the concept of nyctinasty one step further. They too have pulvini and do close at night, but during the day, seem to be constantly readjusting themselves. The fire fern (Oxalis hedysaroides ‘Rubra’), not a fern at all, is a red-leaved oxalis sometimes grown as a houseplant, one of these “dancing plants.”
The telegraph plant (Codariocalyx motorius) seen using time-lapse photography. You can actually see it move, but not quite that fast! Source: gfycat.com
The telegraph plant (formerly Desmodium gyrans, now Codariocalyx motorius), is another occasional houseplant with seemly motorized leaves.
Both plants will only perform when conditions are fairly warm and humid, but if you sit in from of one and watch patiently, you’ll see each leaf seems to be slowly moving, giving the impression the plant is lazily dancing. The fire fern will also react to touch, at least to a slight degree, but more about touch sensitive plants later.
The carambola (Averrhoa carambola) has leaves that move all on their own. Source: biogeodb.stri.si.edu
The tropical fruit carambola or starfruit (Averrhoa carambola), in the Oxalidaceae, likewise has leaflets that both close up at night and move visibly, although slowly, during the day, all on their own … if you watch them patiently!
Response to Touch
Plants that react to touch are certainly the weirdest of all plants with leaves that move. This phenomenon, known as thigmonasty or seismonasty, occurs when something touches or shakes the leaf. And some will also react when you hold a match up to them. This can be incredibly rapid and is certainly visible. Again, all these plants close up at night and, again, it’s pulvinus at the leaf or leaflet’s base that empties rapidly, causing the leaf folding. Studies show that there is even an electrical current that runs between the pulvini on many of these plants, almost like nerves in animals, plus there is also a chemical reaction involved.
Sensitive plant (Mimosa pudica). Source: worldoffloweringplants.com
The best known thigmonastic plant is the sensitive plant (Mimosa pudica), a legume also known as sleepy plant, dormilona, touch-me-not or shy plant, a decent if usually short-lived houseplant easy to grow from seed … and also a pernicious and quite prickly weed in tropical countries. A light touch will cause a single leaflet of the bipinnately compound leaf to fold inward, a firmer touch will lead to the whole leaf drooping and shaking the plant will cause all its leaves to collapse. If you run a finger down the leaf, the leaflets will close like dominoes, as in the photo below. Yet if you leave the leaf alone, it will recover in just 15 to 30 minutes.
Mimosa pudica leaf closing. Source: Mimosa_Pudica Hrushikesh, Wikimedia Commons
It’s thought this quick reaction to touch helps prevent foraging by grazing animals. I mean, wouldn’t you stop eating if you thought you were biting into a luscious plant, then the leaves all collapsed after your tongue touched the first one, leaving the plant looking barren, unappetizing and full of (previously hidden) thorns?
M. pudica is the most commonly grown sensitive plant, but there are some 400 other species in the genus Mimosa, both herbs and shrubs, all sensitive to touch to at least some degree. There is even a hardy sensitive plant (zone 5) that can be grown as a perennial, M. nuttallii.
Note that these are true mimosas, not the trees and shrubs often called mimosas and which are actually very different, non-sensitive plants with similar pinnate leaves such as Albizia julibrissin (silk tree) and several acacias, including Acacia dealbata (blue wattle or mimosa).
There are also several species of “aquatic sensitive” (Neptunia spp.) with leaves much like those of the sensitive plant that react to touch in a similar fashion. As the common name suggests, they grow in water or at least under very boggy conditions.
Little tree plant ((Biophytum sensitivum) has leaves that move. Kenraiz, Wikimedia Commons
Less well known is the little tree plant (Biophytum sensitivum), a small herbaceous houseplant in the Oxalidaceae that looks like a tiny palm tree and is sometimes used as a tree substitute in terrariums and fairy gardens. It is modestly touch sensitive … but its leaves move all on their own much of the time, albeit quite slowly.
Finally, the partridge or sensitive pea (Chamaecrista fasciculata), a fairly common annual species of legume native to the eastern United States, also has pinnate leaves that close at night … and are slightly sensitive to the touch during the day.
Touchy Feely Carnivores
The other group that includes plants sensitive to touch are carnivorous plants or, more correctly, insectivorous plants.
Venus flytrap (Dionaea muscipula) with its leaf traps. To learn how to grow this capricious plant, read No Hamburger for the Venus Flytrap. Source: Citron / CC-BY-SA-3.0, Wikimedia Commons
The best known of these is the Venus flytrap (Dionaea muscipula), often offered as a houseplant, although rarely very long-lived in the average home environment. I already wrote a bit about this plant in 5 Plants with Weird Foliage. It’s bear trap-shaped leaves are dotted with tiny hairs. If an insect touches one hair, nothing will happen. This is believed to be a protection to keep leaves from closing for inopportune reasons, such as when a raindrop or a fallen leaf touches it. However, if the hair is touched a second time within 20 seconds, or if a second hair is touched within the same time limit, the cause is probably a wandering arthropod and the trap closes rapidly, in one tenth of a second. After that, the insect is slowly digested, then the trap opens again. It takes 5 to 14 hours for the trap to reopen after a false alert, while actually digesting an insect can take 10 days or more.
The trap leaves of bladderworts (Utricularia spp.) do their job underwater, so it’s not easy to see them catch their prey. Source: wetland-plants.co.uk
Less well-known than the Venus flytrap, bladderworts (Utricularia spp.) are even faster. Their bladder-shaped trap is small modified leaf, so designed that when it is “set,” a vacuum forms inside the bladder. If a water flea or other small invertebrate touches the sensitive hair on the outside, the trap opens, instantly sucks in the creature, then closes. The whole process only takes ten to fifteen thousandths of a second.
Gardeners won’t likely find this trap as fascinating as that of the Venus flytrap, as all of this action takes place more or less out of sight underwater or even underground in soggy soil, as bladderworts are bog or aquatic plants.
Some sundews (here, Drosera capensis) have leaves that will (slowly) wrap around the insects they have caught. Source: Noah Elhardt, Wikimedia Commons
Other insectivorous plants show some leaf movement. Some sundews (Drosera spp.) have leaves that will slowly wrap around their prey once it is glued to the sticky glands that cover them, but this happens so slowly you’d need a time-lapse camera to notice. Butterworts (Pinguicula spp.) leaves also roll up slightly when they trap a prey item, but their movement is even less impressive than that of sundews.
Leaves that move: one of Mother Nature’s little surprises!
How Does the Mimosa Pudica Move Its Leaves?
Finally, we get to the important question. How does this plant move? It turns out, this simple question that I had after touching the plant has led me into one of the most complex things I have ever come across. I will do my best to explain it, but I will also put some excerpts from some experts below for those a little more intelligent than I.
Our Simple Explanation
This plant has sensors that detect vibration. The Mimosa Pudica reacts once its sensors detect touch or vibration. This process is called Thigmonasty.
You may think that the plant has a 'default' position of open and upright, but from all of our research, it seems as though the default position is actually down and folded. When the plant is open, there is water inside cells that apply force via pressure against the cell walls. This is known as turgor pressure.
When the plant sensors vibration, the plant releases a number of chemicals including potassium ions. These chemicals cause the cells that are under pressure from the water to lose pressure. The lack of pressure sends the Mimosa Pudica back to its default state of folded and droopy.
The Complex Explanation
Here is what the professionals at ScienceABC had to say about why the Mimose Pudica leaves fold:
The movement of plants caused by touch stimulus is known as Thigmonasty. In this mechanosensory response, water within the cells and other cell contents apply a certain amount of force against the cell walls of the plant this is called turgor pressure.
It is due to turgor pressure that the leaves of this plant stay upright unless disturbed externally. Now, when you touch or shake the leaves (known as seismonastic movements), the swollen base of the leaf stalk (called the ‘pulvinus’), which contains certain contractile proteins, is activated.
When disturbed externally, certain regions of the plant trigger a release of various chemicals, including potassium ions, within the body of the plant. These chemicals make water and electrolytes flow/diffuse out of the cell, resulting in a loss of cell pressure. This causes the cell to collapse, which squeezes the leaves shut. Stimuli, in the form of touch, is sometimes transmitted to neighboring leaves as well, causing leaves to fold.