Taking a New Look at Carnivorous Plants

Photo by Gayla Trail  All Rights Reserved

I just read a fascinating piece via the Telegraph UK that is absolutely blowing my mind.

Researchers at the Royal Botanical Gardens Kew have conducted a study looking into plant behavior, specifically carnivorous plants, and are concluding that there are hundreds more carnivorous plants out there in the world than previously realized. Many of which are common to our own vegetables gardens.

The one that makes the most sense to me based on personal experience is nicotiana. I grow Nicotiana alata every year in pots up on my roof and have observed that the leaves are incredibly sticky and attract gazillions of insects throughout the growing season. In fact, I often position the plants in problem areas as a way to attract and kill aphids and other small flying insects. And yet somehow, I never thought to identify this unique ability as carnivorous!

Another plant mentioned is the common, often banal and overrated petunia. I grew petunias this year by chance, something I said I’d never do, ever. But then some were sent to me and I actually sort of liked the variety and the next thing I knew they were potted up and growing alongside the chives and some variegated marjoram. Throughout the season I noticed that this particular petunia had incredibly gummy leaves and attracted legions of tiny, flying bugs all over the leaves, stems, and even the flowers, not at all unlike the nicotiana.

But did I ever think to identify this plant alongside the likes of a sundew or pitcher plant? I should know from studying so much postmodern theory in university, the power that “naming” has to subvert and even define the way we classify or contextualize things. This is a fantastic example of that power at work.

The third example that I find most fascinating are tomatoes and their little sticky hairs. Botanists are now saying that the plants can trap (most of us tomato gardeners know this) and kill insects with these hairs and as the insects die they fall into the soil and are absorbed as nutrients. That’s the real clincher here, because classifying a plant as carnivorous is often about identifying that the plant has adapted to killing insects for nutritional use. I got as far as observing that they could kill, but did not go as far as asking whether or not they were then absorbing the insects as supplemental nutrition. But even if the stickiness and trapping ability is only defensive, isn’t that enough given that the plants are still killing the insects?

This is fascinating stuff and has made me realize how much more conscious I would like to be in the observations I make as I tend my gardens. There is so much amazing stuff to learn and discover in the smallest, day-to-day muddling we do as gardeners, don’t you think?

Gayla Trail
Gayla is a writer, photographer, and former graphic designer with a background in the Fine Arts, cultural criticism, and ecology. She is the author, photographer, and designer of best-selling books on gardening, cooking, and preserving.

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15 thoughts on “Taking a New Look at Carnivorous Plants

  1. Wow – this is amazing info re: petunias & nicotina! I wonder if pairing one of them up with basil would keep the aphids off the basil?

    Will have to make note to try this next year!

    ps – I’ve never really liked petunias either, but if I can make them work for me…

  2. Well, that’s kinda iffy, because including petunias, tomatoes, and nicotiana requires changing the definition of “carnivorous”. Ever since Charles Darwin’s research 150 years ago, the standard for declaring a plant carnivorous is that it has to be able to attract prey, capture prey, and digest prey. Some varieties that are otherwise definitely carnivorous fudge the last: the cobra plant, Darlingtonia californica, doesn’t secrete its own digestive enzymes and therefore has to depend upon bacterial action, and the odd snare trap Roridula can’t digest prey at all, so it lives in symbiosis with a species of ambush bug that eats snared prey and then defecates on the leaves. (Roridula leaves actually have channels to collect the feces and absorb the nitrogen and phosphorus.)

    What this means is that a lot of plants that seem to be carnivorous might be what’s called “protocarnivorous”. The triggerplants of Australia are a great example: the flower scapes are covered with tiny sundew-like sticky hairs that sometimes catch prey, but also catch a lot of other items, such as pollen grains, which can also be digested. I’m currently working on a scientific paper on some of these strategies, and how fully carnivorous capabilities could have evolved from unrelated behaviors, and it’s shaping up to be _interesting_.

    Oh, and if you want two other plants that may be protocarnivorous, take a look at the passionflower Passiflora foetida and the devil’s claw Ibicella lutea. Both of these are fascinating plants in their own right, but they also have the ability to attract and capture insects. It’s just a shame that nobody’s found any evidence of digestive enzymes being secreted to digest them…so far.

  3. I have noticed this in the past with my pineapple sage! It NEVER has any pest issues and I constantly kept finding flies/gnats stuck to the hairs. It was sort of creepy actually! Sadly, I didn’t dig mine up this year and the cuttings didn’t take, so I may be screwed next year on that, some basils, and lemon balm. Stupid busy year.

  4. Wow, unexpected yet unsurprising… I grew a cherry tomato plant for the first time this year, and I did notice dead mosquitoes and such stuck to its stem. Now it makes sense!

  5. Hmmm, that’s a really interesting theory…but I don’t know if I would agree with it.

    I wouldn’t call a plant with pubescent or sticky leaves and stems carnivorous just because it can indirectly gain nutrients from casualties of its fuzziness/stickiness. The presence of pubescence is generally a barrier to insect predation.

    In a different example,take a poisonous plant such as foxglove. If someone’s dog or cat eats foxglove and dies at the foot of the plant, that doesn’t really make the plant a carnivore just because it may use nutrients from the decaying animal.

  6. Paul: Thank you for offering up some further definitions. We were discussing this over lunch and I realized that I had left the digesting part out in my post. I was thinking that there are some similarities between a plant like nicotiana and pinguicula; however, pings have digestive enzymes (or something like that. I’m not familiar enough with the biology of each plant) to directly digest prey. The article didn’t say anything about nicotiana as an example but I’m guessing not. Then again, they do probably indirectly absorb some nutrients from the decaying insect bodies, but if you’ve ever looked closely at the leaves, you’ll notice skeletons that stick around for long periods of time, whereas with pings they are absorbed.

    I had never heard the word, “protocarnivorous”. Your work sounds fascinating!

    Daedre: Good points. I still think it’s interesting even if this doesn’t lead to using the term “carnivorous” as Paul indicated. I’m just excited to have some new inspiration that shifts my thinking even a little bit.

  7. That was a really cool article. I’d noticed the nicotiana and the petunia ‘capturing’ insects before, but I’d never thought of the tomato. Which makes me respect it a little more.

  8. Many kinds of bromeliads collect water in a reservoir they have at the crown of the plant. This naturally has the tendency to capture and drown some insects. Scientists have recently identified digestive enzymes in the fluids of certain varieties of bromeliad, suggesting that they are actually digesting the bugs. However, they only produce a few enzymes, which means that they are just beginning this evolutionary journey.

  9. Well, that’s where it gets interesting, Ed. Two genii of bromeliad, Broccinia and Catopsis, have truly carnivorous members, because they actively produce digestive enzymes in the water in their wells. The problem is trying to discover others, and making sure that (a) the enzymes are produced by the plant itself and not by some symbiotic organism with its own agenda and (b) the plant actually absorbs the nutrients freed by those enzymes. There’s still a LOT of work to be done with carnivores, which is why I tell kids that ask me about botany careers to go after them. Between this and symbiotic relationships with fungi, you’ve got a few thousand Ph.Ds to fill before the research becomes even close to being done.

    Oh, and Gayla? If you get the chance, head over to http://www.carnivorousplants.org and check out the “Carnivorous Plant Newsletter”, because right now is one of the most exciting periods for carnivorous plant research since the height of the Victorian Era. I’m not exaggerating in the slightest, especially since people are going back and reevaluating a lot of species that are best described as protocarnivorous. The triggerplants are a classic example: they comprise a significant portion of Australia’s flora, going in size from tiny near-herbs to small trees. (They get their name because their flowers bear a small column that literally pops visiting insects with pollen, and the movement is usually faster than the human eye can follow.) They produce protease, a known protein enzyme, along their flower scapes, but most of the scapes are so small that they’d only be able to catch tiny insects, and only during blooming season. I have my suspicions as to what they’re really catching, but that’s what the paper is for.

  10. Paul, I follow mycology more than I follow botany and I agree with you. There is a lot of work to be done. The science of mushroom cultivation is growing rapidly. Interestingly, they have found a carnivorous mushroom as well. Pleurotus ostreatus, the pearl oyster mushroom (yes, the kind you get at the grocery store) has been observed to produce chemicals that attract and then stun nematodes. The fungus then grows around the nematode and enters through the mouth, consuming it. When I got beneficial nematodes to solve my problem with fungus gnats in my mushroom growing, it worked in all but the oyster mushrooms.

  11. Amazing. I have serious in-house bug problems because I shove everybody outdoors during the warm months. When I haul these flowering plants indoors, they almost always bring along a bugger or two. I keep a a couple of carnivore plants in the window to make short work of the bugs. But — pretty indoor petunias? And flowering nicotiana? I excited to give these a try…

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