On April 17th, 2018 we learned about

Describing, and disabling, a carnivorous plant’s version of consciousness

“Wait, how do plants know things? Do they know things? They can’t, right?”

My third-grader’s brow furrowed as she ran scenarios over in her head. Plants aren’t the same as animals. They don’t have muscles to move with. They don’t have eyes like we do, and no brain to do any thinking. Nonetheless, they are known to follow the Sun, open and close flowers, and even react to the sound of predators eating their neighbors’ leaves. How was any of this possible without the anatomical gear we depend on to do any of those jobs?

It’s a tough question, and we don’t know all those answers yet. The sound sensory in particular is quite odd, but fortunately, some very reactive plants have helped botanists figure out how a plant can sense and respond to stimuli without nerve cells and a brain to do so. Because carnivorous plants like the Venus flytrap (Dionaea muscipula) and sundew plants (Drosera) have to actively trap their prey, they need to operate in a time-frame that matches the critters they want to catch. To do that, the plants are relying on so-called trigger hairs that essentially give the plant a way to “sense” when something has touched it.

As the titular fly lands on the attractively-scented “lobe” at the end of a leaf, it’s likely to bump into one or more trigger hairs. Unlike your nerve cells, those hairs don’t report back to any brain to trigger further activity. Instead, they create an action potential, which is an electrical charge that builds up in the trigger cell, eventually reaching a threshold where it gets discharged to the next cell, and the next, and the next. Eventually, this signal reaches the plant’s version of a muscle cell, which either expands or contracts to change the water pressure along the joint of the mouth-shaped lobe, causing it to close shut on the bug. With further stimulation of those trigger hairs, the flytrap will start to excrete digestive enzymes to it can actually eat its prey.

Turning off the trigger hairs

Even though trigger hairs aren’t exact matches for animal nerve cells, they’re close enough that they can be used to study the effects of the general anesthetics we use on animals. Even though those drugs are used every day to numb and temporarily paralyze people in surgery, we don’t know exactly how they do it. By using them on reactive plants like Venus flytraps and the “shy plant” Mimosa pudica, researchers are getting closer to understanding the exact cellular mechanisms that make modern surgery possible.

The answer seems to go back to the idea of action potentials, and how they get started in the first place. In both the plants trigger cells and animal nerves, a charge is built up on the outside of the cell membrane or wall. In the membrane are openings called ion channels that open and close when specific molecules are present to unlock them, a bit like a key opening a gate. Charged molecules, ions, can then move into the cell, helping it accumulate a larger charge, until eventually it triggers the release of an electrical charge to kick off another cell.

Paralyzing the plants

When carnivorous plants were subjected to anesthetics like diethyl ether, their trigger cells became unresponsive. The shy plant didn’t curl its leaves. Flytraps didn’t close after being poked. More importantly, no charge was detected at the plants’ trigger cells, indicating that the ion channels weren’t opening, heading off any action potential before it started. A second test with the roots of a mustard plant, Arabidopsis thaliana, found that the lipids, or fat proteins, in the cell membrane were being disrupted, helping researchers narrow their focus even further.

This wasn’t done to numb Venus flytraps, of course. They seem to be quite good at regulating their own activity already; they only close if multiple hairs have been touched, don’t usually close down on their pollinators, and reserve digestive enzymes for when they really have lunch in their clutches. Instead, this work may help us understand and then design better anesthetics for humans and other animals, taking some of the trial and error out of how we temporarily stop each other from sensing the world around us.

Source: We can make plants pass out—with the same drugs that mysteriously knock us out by Beth Mole, Ars Technica

On April 15th, 2018 we learned about

Beyond bugs, mammals, birds and reptiles play big roles in the pollination of flowering plants

On paper, the tongue of a Pallas’ long-tongued bat (Glossophaga soricina) may sound a bit like something from a horror movie. The South American bat’s tongue is made of spongy, erectile tissue, allowing it to increase its length by 50 percent when engorged with blood. It’s covered in an array of tiny, densely-packed hairs, which then stand perpendicular to the tongue when fully extended, allowing it to better capture the fluids the bat devours to stay alive. In practice though, none of this seems very grotesque, because G. soricina only uses its tongue to lap up nectar out of flowers, placing this bat in a niche closer to a honeybee than a vampiric parasite.

Scientists studying pollinators have found that the importance of vertebrate pollinators like G. soricina may be widely underappreciated. For all the attention played to pollinating bees and butterflies, a large number of plant species largely depend on bigger critters like bats, mice and even lemurs to fertilize their flowers. These aren’t strictly fringe cases either, as some flowers have evolved to be highly specialized, and thus dependent on just the right species of mammal or bird to be able to reproduce.

Nectar-eating bats and birds

Among mammals, bats are the most common pollinators, sometimes accounting for 83 percent of fruit production in a geographic region. They’re known to pollinate close to 530 species of plants around the world, often in relatively exclusive arrangements. For example, the blue agave cactus (Agave tequilana) which is used to make tequila, only open their flowers at night in order to attract greater (Leptonycteris nivalis) and lesser (Leptonycteris yerbabuenae) long-nosed bats. These bats don’t have hairy tongues, but the hair on their bodies collect and spread pollen just like the fuzz on a bumble bee.

As the specialized beak and tongue of a hummingbird indicates, many species of our feathered friends also act as important pollinators. Beyond hummingbirds, 920 species of bird are known to spread pollen between flowers, and are estimated to account for five percent of flower fertilization where they live. In more isolated environments, like islands, that number goes up, with birds being responsible for at least ten percent of flower pollination.

No need to fly to flowers

The success of pollinating bees, bats and birds may suggest that flight is somehow necessary to pollinate a flower, but that’s not the case. Any animal that wants to sip nectar without destroying the flower that produced it can potentially act as a pollinator, which has lead to at least 85 plant species around the world that get regular visits from non-winged mammals. Mice, squirrels, possums and lemurs may all stick their noses into flowers enough to transport pollen. Even without fur, bluetail day geckos (Phelsuma cepediana) can act as pollinators, carrying sticky pollen on the tips of their noses.

As humans become more appreciative of how insect pollinators help keep ecosystems alive, this research shows that we need to also consider the bigger-bodied pollinators as well. As policies and even substitutes are being developed to help protect creatures we associate with plants humans grow on farms, we need to make sure the wider range of pollinators around the world are protected as well. After all, some of these pollinators have become very adept at their sticky, hairy line of work, and won’t be easily replaced.

Source: Lizards, mice, bats and other vertebrates are important pollinators too by Ecological Society of America, Phys.org

On January 21st, 2018 we learned about

Chile peppers produce more spicy capsaicin when they’re fighting more fungi

Bugs make food taste better, at least in the long run.

From the crisp snap of wasabi to the soothing bitterness of coffee, many of our favorite flavors have been created in response to some kind of predatory insect. Bitterness is generally a sign of toxicity, which in foods like broccoli or coffee beans, evolved to deter bug that would otherwise destroy a plant’s chances of reproduction, usually by eating fruit without dispersing its seeds. Pepper plants take this mouth-watering defense up a notch, trading bitterness for spicy capsaicinoids, like the capsaicin found in a jalapeno pepper. It’s less subtle than broccoli’s bitterness, but it also has to pull double duty, repelling both insects and fungi that would harm the pepper.

More parasites means mas picante

There are many of pathogens that can harm a plant, but a pepper’s capsaicinoids probably evolved to help fight fungi that target their seeds. Ideally, a pepper, as the seed-carrying fruit of the plant, would be carried by an animal to a new location where those seeds could be dispersed. Fungi then pose a specific threat because they consume the seeds themselves, wasting all the resources the plant put into growing the seeds and fruit. Capsaicinoids help fight the fungi as well as the insects that help the fungi gain access to seeds in the first place.

Researchers studying capsaicinoid production in various peppers found that the plant’s location played a big role in how spicy they’d turn out to be. Cooler areas produced milder peppers, while hotter locales produced spicier fruit. Focusing in on the Capsicum chacoense pepper from Bolivia, researchers found that hotter peppers were first attacked by insects, and that the scars left in the fruit by those bugs provided entry points for fungal parasites. So the plants that were at more risk of fungal infection then produced more capsaicin to act as a bigger dose of fungal protection. This is likely why the seeds of many chiles pack a much bigger punch than the flesh of the fruit itself- that delicious burn is concentrated where it’s needed most.

Bland for the birds

So if fiery peppers evolved to be avoided by insects and fungi, what creature provided the proper seed dispersal for these plants in the first place? While humans have come to enjoy the burn of a good chile pepper, most mammals aren’t so keen on a spicy dinner. Birds, on the other hand, don’t have capsaicinoid receptors in their mouths, leaving them to enjoy the vitamins, sugar and fiber found in a pepper without any sense of the burning we get to experience. The birds are probably happy with this arrangement, but it’s hard not to feel that they’re missing out on the pleasurable pain a good pepper can really add to your meal.

Source: There's a fungus among us and it's making peppers spicy by Jennifer Tsang, The Microbial Menagerie

On January 3rd, 2018 we learned about

The word pineapple made more sense when everything was apples

Pineapples obviously don’t resemble apples, but they used to. This isn’t because pineapples used to have thin peals and white flesh before humans started cultivating them, but because people’s concept of what an apple is has changed since the fruit was first identified by European explorers. For hundreds of years, the word apple could be used for just about any unknown fruit, even if they were in no way related to plants in the Malus genus. Following this logic, peaches were first known as “Persian apples,” and bananas were once “finger apples.” This then leaves us with the “pine” in name pineapple, which still doesn’t make much sense.

Since pineapples don’t even grow on trees, it’s clear that nobody thought these tropical fruits were somehow growing on spruce or redwoods. What they did think is that pineapples looked a lot like pine cones, which, in 16th century, were still called pine apples themselves, since they produced seeds while growing in a tree. So from a 16th century perspective, pineapples do look like their namesake, at least before we changed the name of the plants that were being referred to. In the case of pine cones, the use of the word cone was borrowed from the Greek kōnos, and eventually passed from more academic botanical discussions to common English by the 18th century.

When is an apple not a fruit?

Apple is obviously no longer a generic term, now used exclusively for expensive computer hardware or the fruit of the Malus pumila tree. The word fruit itself is now our best generic term for tree-bound produce, although it too has a narrower definition than it used to. In the late 12th century, fruit could be any “useful” portion of a plant, with etymological roots in words for enjoyment and satisfaction. At some point, it could even be used for any product grown from soil, from nuts to veggies, and so the idea of a reward being the “fruit of one’s labor” barely qualifies as a metaphor.

Today, fruit covers a lot of the ground that the word apple used to, but it has also gained a strict, botanical definition. The funny thing is that since fruits are “seed-bearing structures in angiosperms formed from the ovary after flowering,” pine cones, as the original pineapples, can’t really be considered fruit at all. With pineapple’s linguistic connections being erased bit by bit, maybe it’s time English speakers simply joined the rest of the world and picked up the word Ananas. It wouldn’t be any more confusing than what we’re saying now.

Source: A Pineapple Is An Apple (Kind Of), Merriam-Webster Word History

On January 1st, 2018 we learned about

Scientists find the molecular mechanisms that help flowers survive their own deadly fragrances

Smelling nice is a luxury for humans. Skipping deodorant isn’t really going to hurt us, although it may bother whomever we stand next to on the bus. For flowering plants, emitting a pleasant, or maybe just strong, smell isn’t a choice. Beyond helping to attract pollinators and signal growth cycles, researchers have learned that flowers must get their attractive odors into the air, because holding them inside would be fatal. Now a series of experiments has figured out exactly how flowers keep themselves safe from their own delightful fragrances.

The gases that we usually refer to as a flower’s fragrance are technically known as “volatile organic compounds,” or simply volatiles. While volatiles tickle our smell receptors when they enter our nose, they’re toxic to the plant cells that produce them. The realization of this critical fact forced scientists to rethink their original model of how flowers release volatiles so animals can smell them, which stated that the fragrant molecules passively diffused through cell walls into the atmosphere. However, that process would actually be much to slow for the health of the plant, prompting further investigation into how plant cells send their scents into the air.

Isolating petunias’ volatile pump

The first part of the study looked at petunias, as they release very few volatiles as buds, but really pour them out when the flowers have bloomed. The contrast between these two phases allowed researchers to look for genes that were more or less active at either time, revealing which genes and therefore molecular mechanisms were being cranked up to push more volatiles out of the flower’s cells. The answer was a type of ATP-binding cassette transporter, which flowers use to not only move volatiles, but other compounds like a leaf’s wax coating as well. The volatiles were actually moved out of the cell thanks to combinations of hydrophilic, or water-attracting, and hydrophobic, or water-repelling molecules. The volatiles themselves are also hydrophobic, and so the right combination of similar and contrasting molecules could effectively shove the volatiles out of the cell after they were produced.

To test this hypothesis, researchers manipulated the transporter genes in petunias and other plants. In flowers that presumably relied on these genes to eject volatiles, the genes were suppressed, leading to less fragrant blooms and eventually more dead cells thanks to a build-up of volatiles. On the flip side, the transporter genes were added to non-flowering tobacco plants, then dosed those plants with potentially dangerous volatiles. As expected, tobacco that had the volatile transporter genes could keep its cells alive by pumping out volatiles. Normal tobacco plants that lacked this extra mechanism couldn’t cope, and died like the genetically modified petunias mentioned earlier. Thanks to these experiments, scientists now know exactly how flowers survive their own scents, and may be able to further control volatile output in the future.

Source: Stopping to smell the roses? You’re inhaling flower farts by Abrahim El Gamal, Massive Science

On November 19th, 2017 we learned about

Analysis of potatoes’ genetic past identifies opportunities for better breeding in the future

Don’t take this the wrong way, but you’re simpler than a potato, at least on a genetic level. A study of the lowly spuds’ genetic history has found not only how complex the modern potato’s genome is, but that it may be overdue for some innovation. This interest in potato evolution isn’t because potatoes are slacking off in meeting their mutation quota, but that potatoes are humanity’s third most important crop worldwide. If nudging the right gene might yield healthier french fries, we might all be better for it.

A modern, cultivated potato has a lot of genetic material to look through, with over 39,000 genes in it’s genome. That’s more than a human’s 20,000 genes, and even more than potatoes own ancestors. Wild potatoes, as ancestors to the potatoes we grow to eat, are much simpler in comparison. They reproduce with what’s known as a diploid genome, with two sets of chromosomes per organism. This can be accomplished with seeds and berries, a feature that has obviously been bred out of their domesticated counterparts.

Taming the tuber

In the last eight- to ten-thousand years, human intervention changed a lot about these starchy members of the nightshade family. A domesticated potato can reproduce asexually, and now sports a tetroid genome, with four sets of chromosomes per individual. To potatoes out of the Andes mountains, we’ve altered everything from their pest resistance to the the plants’ circadian rhythm, as growing outside high mountain ranges meant differing amounts of sunlight per day. These sorts of mutations are among the 2,622 genes that transformed the potato into the staple starch we now find at the grocery store.

While researchers would like to see further change in the potato genome, they’re mostly looking to achieve it the old fashioned way. In the relatively short time since potatoes were first domesticated, farmers have been able to make some significant changes to these plants. With that said, there is concern that more recent breeding efforts have hit a bit of a ceiling, with no major improvements to speak of in the last 100 years. With more specific information about the potato genome, we may be able to make more significant gains via more carefully planned breeding programs. So as much as you may enjoy your mashed potatoes today, farmers may be able to offer an even better option in the not-so-distant future.

Source: Examining Potatoes’ Past Could Improve Spuds Of The Future by Layne Cameron and Robin Buell, MSU Today

On October 15th, 2017 we learned about

The plants that deter their demise by becoming more toxic and doubling their DNA

While people often become vegetarians or vegans to avoid causing harm to animals, there’s plenty of evidence that plants aren’t much happier about being eaten than any animal. Sure, fruit can be tasty and enticing so that a plant’s seeds will be distributed, but the leaves and stems themselves are more likely to be bitter or dangerously toxic for interested herbivores. If the plant itself is eaten, it will probably miss its chance to reproduce, a goal so significant that some plants actively respond to threats as they occur. This may mean trying to regrow lost leaves or stems that were chomped off. Or it could mean a plant will warn their kin to increase their production of nasty toxins to scare off incoming insects. Or, in plants known appropriately dubbed “overcompensators,” a single plant will adopt both strategies at once, fighting back the threat of being consumed so vigorously that they end up better off after being bitten than if they lived their whole lives untouched.

The ideal scenario for an overcompensating plant is to be nibbled on enough to trigger its defenses, without causing so much damage the plant can’t carry on. Once a primary stem is bitten or clipped, plants like the mustard Arabidopsis thaliana will increase their growth rate, regrowing the lost stem two to three times faster than it originally grew. To make sure the plant isn’t simply restocking some herbivore’s buffet, the plant will also increase the amount of toxins it produces so that it theoretically won’t get munched on again. This two-pronged strategy not only helps keep the plants alive, it may even give them a boost, as they have been found to enjoy greater reproductive success, spreading more seeds, than plants of the same species that never responded to danger.

Pumping out proteins

As from the energetic cost of tacking both toxins and regrowth at once, the weird part of these abilities is just how the plants make themselves grow faster. Normally growth involves a cell cloning its DNA then dividing into two so that each resulting cell is copy of the first, complete with cells walls, mitochondria, etc. Those cells can then do whatever job the original cell was doing before, like making proteins vital to the plant’s metabolism. These overcompensating plants speed up growth with a process called endoreduplication, which tries to get twice as much out existing cells, rather than having them split themselves in two. A cell’s DNA will be copied, but both copies stay put and go to work. This means that that first cell can kind of multitask, encoding two proteins simultaneously using both strands of DNA, but without the overhead of a second cell’s other organelles. As it happens, the molecular triggers for endoreduplication also help kick off toxin production, making overcompensating a rather elegant package for a plant to adopt.

Researchers are hoping that this package is also transferable to other plants. While 90 percent of herbaceous flowers currently engage in endoreduplication, there could be big benefits if commonly farmed crops used it more often. Responsive toxicity levels could reduce the amount of pesticides needed to protect plants like cotton. Higher growth rates would be appreciated in all kinds of crops, shortening the amount of time necessary to get a full year’s yield. There’s more work do be done, but farms may someday be able to significantly boost their crops’ growth with just a bit of well-intentioned pruning.

Source: Some plants grow bigger – and meaner – when clipped, study finds by Diana Yates, Illinois News Bureau

On September 20th, 2017 we learned about

Policing and preventing the burl poaching that puts redwood forests at risk

How much would you pay for a piece of a tree’s metabolic dysfunction? What if was the shape of a wall clock or coffee table? Even if you’re hesitating, there’s enough demand for what’s essentially deformed wood that national and state park rangers have begun working with police to deter poachers. The wood, known as burls, is valuable enough that so called “midnight burlers” are sneaking into parks under the cover of night, removing portions of trees and possibly putting the forest at risk.

Twisted tissue in tree tumors

You’ve probably seen a burl at some point, as they’re not uncommon on large trees. Thanks to an injury or just exposure to infected soil, a tree will become infected with bacteria like Agrobacterium tumefaciens or fungi like Exobasidium vaccinii. The pathogen will alter the plant’s DNA, causing the metabolism speed up growth in one part of the tree, essentially resulting in a large, woody tumor. As the growth gets bigger, it can bulge out from a tree trunk, sometimes ending up with a larger diameter than the tree itself. Trees can survive with one or multiple burls for many years, although there is evidence that they’re a bit of a drain on the tree’s health, as burl-carrying trees tend to die earlier than their burl-free kin.

While the trees don’t benefit from growing burls, woodworkers love them. When cut open, burls reveal a much more chaotic, randomized structure than healthy trunk. The wood grain in a burl is swirled and uneven, often containing multiple shades of color, and can be polished for rather spectacular effect. Importantly, it’s also just very different from healthy wood, and that rarity is what’s making it valuable enough for poachers to steal, even out of State and National parks.

Blocking the burlers

California’s redwood forests have been targeted by poachers for the last few years. Morning patrols would turn up massive trees with enormous holes chopped out of their trunks. With over a hundred thousand acres of forest to patrol, there’s been little hope of catching thieves red-handed, as the poachers can cut a burl and deliver it to a buyer in a single night. The wood buyers are somewhat complacent, but aside from weird delivery hours, there hasn’t been a clear way for them to obviously know when a burl has been illegally harvested.

That might be changing though, as rangers and law enforcement have been trying new tactics to slow down the poaching. Careful mapping of which trees were attacked revealed that poachers aren’t picking the best or most hidden burls, but simply targeting trees close to the road. This has allowed rangers to better plan their patrols, reducing the amount of territory they might need to guard each night. After a tree is poached, advances in DNA analysis may soon make it easy to identify which tree a particular burl came from. By making the wood traceable, wood buyers may need to become a little more thoughtful about where their supplies come from.

Fighting for the forest

While trees generally do better without burls, preventing poachers from cutting them off is good news, especially for redwoods. While the burls represent a metabolic disorder, they’re also packed with nutrients. Losing a dense ball of nutrients isn’t great for the adult tree, but it’s also bad for redwoods’ suckers. When the young trees try to start growing, a missing burl robs them of a considerable source of nutrients, hurting the forest’s natural rejuvenation. Additionally, since many poachers are working with chainsaws as quickly as possible in the middle of the night, the cuts to remove the burls are often rough and haphazard, raising the remaining tree’s risk of new infections.

It should be noted that not all burled wood is obtained illegally. Many woodworkers harvest burls from less vulnerable species of tree, and do so in a more responsible way. As demand, and prices, rise, more midnight burlers are likely to try to pass their goods off as legitimate. At this point, it’s in everyone’s interest to make sure the poached wood is kept out of the market, and our living rooms.

My kids said: Maybe if the poachers know that they’re hurting the redwood trees they’ll stop.

That would be fantastic. Unfortunately, poaching markets seem to be tied not just to demand from buyers, but also to downturns in other parts of the economy. Chances are, many poachers feel like they don’t have a lot of choices, and a few thousand dollars for some stolen wood seems like the easiest answer.

Source: How Forest Forensics Could Prevent the Theft of Ancient Trees by Lyndsie Bourgon, Smithsonian

On September 7th, 2017 we learned about

Electrifying plant matter for healthier leaves and better power storage

We’re not far off from plugging in our plants. The boundary between organic, leafy greens and metallic electronics is becoming increasingly blurred, although the end result won’t exactly look like a LED grass or an electrified salad (sadly). Still, there’s an impressive range in where plants and electronics are overlapping, starting with some well-roasted leaves that are may soon be recycled into capacitors.

Using leaves to manipulate a current

Appropriate to their names, Chinese phoenix trees are being reborn in fire as highly conductive carbon microspheres. Thankfully, the whole tree doesn’t need to be destroyed in this process, as the carbon is obtained from dead leaves that pile up in autumn. That convenience aside, you probably aren’t going to start getting capacitors out of your yard waste any time soon, as these leaves are dried, powered, heated for 12 hours at 428° Fahrenheit, mixed with potassium hydroxide, then heated again in rapidly changing temperatures up to 1,472°.

It’s a lot of work, but the payoff is a renewable source of highly porous carbon spheres that may pave the way for a variety of plant-based electronic components. The pores create a very high surface area for the tiny pellets, which may even qualify as supercapacitors transferring three times more power than graphene supercapacitors. The phoenix tree leaves work especially well, but researchers are already looking into other plants like potato skins, corn straw, pine wood and rice straw as other sources of conductive carbon.

Measuring the current in leaves

On the flip-side, if you’re looking to produce more foliage instead of electricity, there’s still a reason to wire up a plant’s leaves. Lightweight electrical sensors are being clipped onto leafy crops to measure how well they conduct electricity in differing soil conditions. Once baselines are established, these tiny variances may help measure exactly when a plant is dried out enough to need a drink, reducing a farm’s water usage.

To make these measurements, a small sensor was clipped to leave on different plants for 11 days. As the plants absorbed more or less water, their leaves would swell or shrink at the same time. That tiny change in thickness would then alter the flow of electricity through the leaf enough to be detected, and could then inform a farmer, or automated irrigation system, when plants were really ready for more water, even if the normal watering schedule didn’t sync up. These measurements were compared against a separate sensor in the soil to verify that they were on the right track. The measurements are complicated by the fact that photosynthesis can also change the flow of electricity through a leaf, but researchers are still confident this system will allow farms to be much more sensitive to their stressed plants.

Source: High-Tech Electronics Made From Autumn Leaves, Scienmag

On August 21st, 2017 we learned about

Thin, smooth bark makes Madrone tree trunks seem cool to the touch

I may need to start petting trees more often. I’ve long known of trees that had particular colors and smells in their leaves and trunks, but I only learned in the last week that some trees hold surprises for your finger tips to discover. The tree in question was a Pacific Madrone (Arbutus menziesii), and was actually hard to miss thanks to its striking red bark peeling off the trunk. The surprise was that the tree was cool to the touch, which is why it’s sometimes called the “refrigerator tree.”

For something cool to the touch, Madrone trees need lots of sunshine to thrive. If conditions are right, they can grow to be nearly 100 feet tall, but at smaller sizes Madrone trees can be mistaken for some of their red-barked relatives, like the Manzanita (Arctostaphylos). Both plants’ eye catching bark grows thin and smooth, but this trait is especially striking in mid-summer when Madrone tree bark starts to peel off the trunk. At that point, a quick touch makes it hard to ignore how much cooler these trees are than the surrounding environment.

Cold or just conductive?

Except that they’re not really cooler. The trees’ temperature is likely the same as any of the other similarly-sized plants that grow near them, just like a paper book is the same temperature as a metal keys sitting in the same room. With sufficient time, the temperatures equalize, but when we touch the metal, or the Madrone trunk, it feels colder. This is because heat is more easily transferred to certain materials than others, and when heat from our hand is conducted away we perceive it as colder. Now, a Madrone tree obviously isn’t metal, but that thin, smooth bark isn’t as good an insulator as the rough, corky bark that you find on most trees. Your hand is able to come into more contact with the smooth surface, and the sap and fluids flowing inside the trunk can then wick your body heat away.

Even if refrigerator trees aren’t actually colder, their unusual bark obviously still stands out from that of their neighbors in the forest. The thin, peeling bark that exposes the trunk may have originally evolved as a form of defense. By shedding the outer layer of bark, the tree can dump any fungi, mosses, lichens or other parasites that tried taking up residence on the red wood. The red itself is likely another form of defense, as the tannins that make up that coloration would be bitter and possibly toxic to animals that might want to munch on the tree, not unlike the colorful bark found on rainbow eucalyptus. It’s good that the peeling is helpful to these plants, because now that they know about these chilled trees, it’s going to be hard to keep my kids’ hands off them.

Source: The Refrigerator Tree by Steve, Nature Outside