Plants with Weird Leaves: Leaves That Move

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Some leaves really like to shake it up! http://www.oogazone.com & freedesignfile.com

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

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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.).

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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

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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?)

Night Moves

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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

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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.”

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.


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Grow Your Own Living Sticky Trap!

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Pinguicula gigantea with the usual contingent of fungus gnats. Source: Noah Elhardt, Wikimedia Commons

Yellow sticky traps have been around for over a century (flypaper was patented in 1910) and gardeners know them well. You put them out near plants susceptible to attack by flying insects and bif, boom, bang!, the annoying little creatures stick to the trap rather than eating your plants.

However, Mother Nature has been making sticky traps for millions of years in the form of plants with sticky foliage. There are many plants that capture insects that way. The more efficient ones are said to be carnivorous, or more correctly, insectivorous plants. Wouldn’t it be wonderful if you could just set out pots of sticky trap plants and watch insect pests fall prey to them? Well, you can. But not just any insectivorous plant.

I’d suggest using butterworts.

What the Heck is a Butterwort?

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One of the Mexican butterworts, Pinguicula moranensis, a parent of many of the hybrid varieties Source: worldofsucculents.com

Butterworts are plants in the genus Pinguicula. There are about 80 species found mostly in the Northern Hemisphere, but also South America, where they grow from the Arctic to the tropics, and from near sea level to above the tree line. Unless you live in Africa or Oceania, there are probably wild butterworts growing not far from where you live.

The name Pinguicula means “small greasy one,” as they’re quite small plants (most measure less than 8 inches/20 cm in diameter) with apparently smooth pale green leaves that seem to be covered in a thin, shiny layer of fat. They’re called butterworts for the same reason. If you look closely, though, you’ll see the leaves are neither smooth (in fact, they’re covered with tiny hairs) nor greasy: it’s not a layer of “fat” that covers the leaves, but rather many fine droplets of clear mucilage.

For indoor use, you’ll want one of the tropical Mexican species (P. moranenis, P. esseriana, P. gigantea and various hybrids), as they are adapted to conditions very similar to those found in the average home. Most will produce dense rosettes of sessile (lacking a petiole), spoon-shaped leaves, looking rather like small, smooth-leaved African violets (Streptocarpus sect. Saintpaulia). Note the leaves often roll up at the edges to keep digested insect liquids from dripping off.

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The flowers (here, Pinguicula moranensis) look a lot like violet flowers. Source: Noah Elhardt, Wikimedia Commons

Even the flowers, usually purple or pink, more rarely red , yellow or white, look rather like the blooms of species African violets, with five petals (two smaller upper ones, three larger lower ones), but borne on taller, thinner stalks. Many of the hybrids, especially, bloom sporadically much of the year … again, much like African violets.

However, in spite of these similarities, butterworts are not related to African violets: the latter belong to the Gesneriaceae family, while butterworts are in the Lentibulariaceae family (the bladderwort family).

How Butterworts Trap Insects

I’ve grown many insectivorous plants indoors over the years—Venus flytraps, nepenthes, tropical sundews, etc.—and if they ever caught any insects, it was only because I supplied them. Not so with butterworts.

If there are any small flying insects in your home, your butterwort’s leaves will soon be dotted with them. Fungus gnats seem to be fatally attracted to them. I haven’t had a true fungus gnat infestation since I began growing butterworts: any fungus gnats that manage to work their way into my plant collection end up stuck on their leaves. And I’m not the only one who’s had success with butterworts as living sticky traps. Some commercial orchid nurseries also use them to control fungus gnats.

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Butterwort leaves (here, Pinguicula colimensis) are covered with shimmering droplets of mucus. Source: Barry Rice, http://www.sarracenia.com

Why are the leaves so attractive to small insects? The principal theory is that the shimmering appearance of the leaf seems to suggest water. It always strikes me that the color of butterwort leaves is such a pale, bright lime green, almost yellow, a color that seems to attract many insects (if most commercial sticky traps are yellow, it’s not for nothing!), so that might also be a factor. And it’s possible the leaves give off some sort of chemical attractant.

Whatever the reason, when the insect lands, it becomes stuck on the mucilage. The more it moves, the more is produced, soon covering and smothering the insect. Then the leaf produces digestive enzymes that dissolve the insect into fluids the leaf can absorb. Note that the leaves often roll upwards along the edges: this is to keep the “bug juice” from washing off in the rain. Butterworts obtain all their minerals from trapped insects: their roots absorb only water.

Fun Fact

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Tätmjölk is the Swedish name used for the yoghurt like product made by curdling milk with butterwort leaves.. Source: Kristofer2, Wikimedia Commons

Adding a butterwort leaf to milk will cause it to curdle, resulting in a fermented milk product notably consumed in Scandanavia.

Reasonably Easy to Grow

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You can grow Mexican butterworts on a window ledge like you would almost any small houseplant. Source: ChrisLamb, www.flytrapcare.com

You can grow tropical butterworts under average household conditions. I grow mine alongside my African violets, as they have similar needs. In other words, give them good light with some morning sun, such as an east window (or, as I do, a spot under grow lights), reasonable air humidity, normal indoor temperatures, etc. They prefer water with a low mineral content, such as rainwater or distilled water. In the winter, when rainwater is scarce, just use water from your dehumidifier.

Keep the potting mix evenly moist throughout the growing season, never letting it dry out, as butterworts have a very limited root system and simply don’t tolerate dry soil. Some people wick water them or leave the pots soaking in a thin layer of water during the growing season, but you can also water from above as you would any houseplant as long as you keep the soil moist.

Never apply fertilizer: like other insectivorous plants, butterworts evolved to grow in soils or other substrates (often moss) that contain no minerals. Thus, fertilizer can kill them. They’ll get their “food” from the insects they catch.

Nor do they seem to tolerate pesticides of any kind, either fungicides or insecticides. If you need to spray your other plants, move your butterworts somewhere else first.

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This Pinguicula esseriana is going ito dormancy. The new leaves in the center are winter leaves: smaller, thicker and are not covered in sticky dew. Source: http://www.thecarnivoregirl.com

With most butterworts, there is a “dormant” period. The tropical types rarely go fully dormant (the temperate ones do, though), but instead start to produce smaller, thicker “winter leaves” that are not insectivorous. During this period, which usually occurs from September/October to March/April, you can grow them cooler, although this is not strictly necessary. However, it is very important that you allow their growing mix approach dryness before watering again. When new, longer summer leaves start to appear, start watering more abundantly again.

That said, I find some of the Mexican butterworts, especially the hybrids, continue to grow throughout the year, especially when kept under lights. If so, just follow the plants’ lead and keep watering them well.

You can try multiplying butterworts by leaf cuttings (tricky) or seed (a bit easier) and commercially they’re produced by tissue culture, but most species will produce offsets you can remove and pot up, something most easily done during their dormant period.

It’s best not to repot butterworts into regular commercial potting mix, because it contains fertilizer. Instead, prepare your own blend, say half peat moss, half perlite or vermiculite, or sphagnum moss with or without a share of perlite or vermiculite. If the mix contains a pinch of lime, that’s not a bad thing either, because unlike other insectivorous plants, mostly from acid growing conditions, butterworts prefer slightly alkaline soil. However, adding lime to the mix  doesn’t seem to be essential.

In spite of the above, some people do use ordinary peat-based potting mix and claim to get wonderful results.

Limited Local Choice

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Butterworts only identified as “starfish plants” (note plant 3) show up in garden centers with other insectivorous plants. Source: www.boomanfloral.com

Butterworts often show up in garden centers among shipments of other insectivorous plants (one company calls them “starfish plants” for reasons unknown) in little plastic terrariums. These are usually hybrids of unverifiable origin and are the cheapest way of getting started with butterworts. Do not leave the plants in these transport terrariums: they’re for shipping purposes only and cut off air circulation, harming the plant if it’s left in one for too long a time.

If you want a wider choice, a better-quality plant or proper identification, you can order butterworts from a specialist insectivorous plant nursery.

Here are a few nurseries that sell them by mail order:

Carnivorous Plant Store (Canada)
Carnivorous Plant Nursery (USA)
Cascade Carnivores (USA)
Exotik.fr (France)
Triffid Carnivorous Plants (Great Britain)


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