When Tumbleweeds Take Over

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Call in the troops! Airmen battle a tumbleweed invasion in Clovis, Colorado. Source: www.cannon.af.mil

For me, tumbleweeds blowing lazily down the street of a ghost town are the very epitome of the American West, but while tumbleweeds may seem bucolic to gardeners in greener climes, real Westerners are getting fed up with tumbleweeds. Iconic or not, they’re a major hassle.

Road overwhelmed by tumbleweeds. The road had just been cleared by a snowplow! CLICK ON THIS: IT’S AMAZING! Source: Tim Tower, http://www.youtube.com.

When the big, round shrub-like masses of dry vegetation break loose from their roots and start to roll, they have to stop somewhere … and that somewhere can be drainage ditches, fences, firebreaks, gardens and homes. You certainly wouldn’t let a child play outdoors when they’re around in any number: that could be fatal! Sometimes so many tumbleweeds build up against homes that people have had to climb out through second-story windows or call neighbors for help. Some homes become entirely covered and can’t be recognized as buildings.

And Western tumbleweeds can be toxic to wildlife (they’re edible when young, then more and more toxic as they mature), hinder traffic and, being highly flammable, are a major fire hazard. Imagine a rolling, burning bush heading towards your home! Their thorny stems make handling them painful (hint: wear thick gloves!) and scratches can cause rashes, itching and inflamed skin in sensitive individuals. Going barefoot in tumbleweed territory is unthinkable and in many areas, you have to protect the legs of pets and livestock to keep them from going lame. And each plant produces up to 200,000 seeds a year. Yikes!

What Is Tumbleweed?

A tumbleweed can be any plant that breaks off and blows around. This one is a giant tumbleweed (Salsola x ryanii), only recently discovered in California. Source: giphy.com

Tough question! The term tumbleweed can refer to many different plants in 10 different plant families. It actually refers any plant sharing the same seed distribution technique. Tumbleweeds can be flower heads or entire plants that spontaneously break free and roll in the wind, spreading their seeds or propagules as they go.

Tumbleweeds tend to found in arid climates with open environments where there are few obstacles to hinder their roll-about distribution method: steppes, savannas, plains, deserts, beaches, etc. They don’t get very far, although may well be present, in dense, green, shrubby environments. Moist soils are an anathema to them: they much prefer drought!

Tumbleweeds in the Garden

You may be growing tumbleweeds without knowing it.

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The flower head of the tumbleweed onion (Allium schubertii) is a typical tumbleweed. Source: www.johnscheepers.com

The huge spherical umbels of rose-purple flowers of the ornamental onion Allium schubertii break off and roll about in its native Middle East environment. It is sometimes called—and why not?—tumbleweed onion. Boophane and Brunsvigia, two extraordinary African bulbs likewise bearing balls of flowers, are also tumbleweeds.

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The so-called Resurrection Fern (Selaginella lepidophylla) is one of the rare fern relatives that is a tumbleweed. Source: Nicole-Koehler, Wikimedia Commons

Or you may have tried (mostly likely in vain) to grow a “Resurrection Fern” or “Rose of Jericho” from a dried-up ball of leaves. Such dried plants commonly are sold as a novelty plant in horticultural fairs and will green up (although rarely come back to life) when soaked in water. The Resurrection Fern is not actually a fern, but a spike moss (Selaginella lepidophylla) and in the wild in its native Chihuahuan Desert, it breaks free and rolls about, spreading its tiny spores.

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Planting of kochia just staring to turn its bright fall color. Source: lookfordiagnosis.com

Another homegrown tumbleweed is kochia, also called burning bush and summer cypress (Bassia scoparia, syn. Kochia scoparia), a garden annual that forms a dense ball of apple green leaves that turn brilliant red in the fall and is sometimes used as a temporary hedge. It too breaks off and rolls away at the end of the season, sowing its seeds far and wide. Although widely available in seed catalogs, growing kochia is illegal in many areas.

The Not-So-Friendly Tumbleweeds

The tumbleweeds devastating California, Colorado, Arizona, New Mexico, Texas and Mexico, just to mention a few hot spots, are quite different from the garden plants described above and indeed, are not even native to the New World, but were imported accidentally from the steppes of Russia in field grains starting in the late 1800s. Others possibly arrived from elsewhere in Asia and one species seems to have come from Australia or Africa.

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When in growth, so-called Russian thistles (Salsola spp.) look nothing like thistles, but rather like shrubs. Source: Pablo Alberto Salguero Quiles, Wikimedia Commons

Because of the Russian origin of the main species and the plant’s thorny leaves, these tumbleweeds are often called Russian thistles. Of course, they are clearly not true thistles (that title rightly belongs to the thistle subfamily of the Asteraceae or sunflower family). Instead, they are placed are in the genus Salsola, now in the Amaranthaceae or amaranth family. Actually, the genus name has been changed to Kali … but I’ve heard rumors it will be moved back to Salsola, so I’ll be using that name in this text.

Confusing Nomenclature

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Most botanists would call these plants Salsola tragus, a sort of “name by consensus” for any plant in the hopelessly muddled Salsola genus. Source: wnmu.edu

Whether you call them Salsola or Kali, the plants’ identification is hopelessly muddled. Traditionally, the North American plants have long been called Salsola tragus, but apparently several very similar species were actually introduced, including S. kali, S. pestifer, S. australis and S. iberica, so it’s rarely clear which species you’re actually looking at. In fact, just to make things more confusing, some of these species have hybridized, creating new species, such as S. x gobicola and “giant tumbleweed” (S. x ryanii).

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The tiny flowers of Russian thistle are pretty enough … when seen close-up. Source: Forest & Kim Starr, Wikimedia Commons

Salsola species are shub-like annuals of varying heights, from 4 inches to 4 feet (10 to 120 cm tall) according to growing conditions, with small, sparse, linear, spine-tipped leaves and numerous narrow, branched, tangled stems. The stems are green, red or striped when young, beige at maturity. The tiny sessile mallow-like flowers have no petals, only sepals. They are whitish to pink, depending on the species.

The plant dries up when the seeds mature, then breaks off at its base and starts its travels, dropping its seeds as it rolls. Plants have been clocked at 30 miles (48 kilometers) per hour on windy days and will often take to the air!

Going Places

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Field filling in with young Russian thistles. Source: Stefan.lefnaer, Wikimedia Commons

Starting theoretically from an accidental introduction in South Dakota in 1873, Russian sage has pretty much conquered the North American continent, being found in 48 US states except Alaska and Florida, northern Mexico and all Canadian provinces, although none of its territories. In more humid climates, it’s mostly found on railrway embankments (plants are carried far and wide by trains) where they thrive in gravel and near the ocean, as it will grow in saline soils, including sand. It has likewise naturalized pretty much all over the world: Australia, South Africa, Asia, Europe and South America.

The extreme drought in the US Southwest has caused a massive explosion of tumbleweed in many areas where it was once fairly rare, since it is extremely drought tolerant and easily fills in where other plants fail.

Stopping a Pest Plant

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Mass burning of tumbleweed in a secure setting. Source: CBS

Control measures so far have been mostly limited to cutting the plant back, spraying it with herbicide and mass burnings of mobile plants, but the USDA is testing specific insects and diseases, including a virus, imported from the plant’s main homeland, Eurasian Russia. Some look quite promising, but the concern is that they may attack other plants and that requires further study.

In the meantime, S. tragus can still be useful under certain circumstances, offering browse and shelter for wild animals, a source of seed for birds, soil rehabilitation and phytoremediation. It also acts as a pioneer plant in disturbed environments, helping to launch ecological successions. It is not very competitive, disappearing quickly when taller vegetation creates shade, and thus will only thrive under near barren conditions. Also, the seeds are short-lived (about two years).

However, the prolonged drought in the US Southwest means the situation has gotten so out of hand in recent years that there is little sympathy for tumbleweed there. Most people want to see it gone … forever!20180425A www.cannon.af.milJPG

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


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.

Leaves that move: one of Mother Nature’s little surprises!20180211A www.oogazone.com & freedesignfile.com.jpg