Plant Defenses: Nature’s Most Clever Survival Tactics

In this episode of Wildly Curious (formerly For the Love of Nature), co-hosts Katy Reiss and Laura Fawks Lapole dive into the world of plant defenses. From the explosive crystals of Diffinbachia that can paralyze predators, to the sneaky neurotoxins of the Australian stinging tree, they explore some of the most extreme ways plants defend themselves. They also discuss more subtle strategies, like the gentle wilting of the Mimosa plant and the surprising role of capsaicin in keeping mammals away from chili plants.

This episode is packed with incredible stories about how plants have evolved to survive, making it perfect for nature lovers, science geeks, and anyone fascinated by the wild world of botany.

Transcript

Hello, and welcome to For the Love of Nature, a podcast where we tell you everything you need to know about nature and probably more than you wanted to know. I'm Laura.

And I'm Katy. And today we're gonna be talking about plant defenses. But first, the news.

I was gonna say, I feel like we need... I almost did the... But that's law and order.

I almost did that.

I ching, ching.

Definitely law and order, not the news. But I do have something that I guess is a murder. I don't know if it is a murder.

A nature murder?

Well, or a muckduck. So my nature news story that we're gonna be talking about is the news around grizzly bear 399. And for anybody that's in any sort of wildlife, anything, you guys have probably heard of grizzly 399.

It's a mother grizzly bear that's been around, I think she was born in like 96. And yeah, she is old, but a very, very successful mother. And she's also very popular because she tends to hang out near highways and roads, which not for the typical reasons, like it's not like she's hanging out near the roads and everything because there's humans there and she associates humans with food.

No, because she does very effectively teach cubs to follow elk herds and rely on the elk and everything like that. But she, the scientists believe that she does this, sticks to human roads because it's just away from the male grizzlies who would kill her cubs. And so she's like smart about it, sort of a smart mom.

Smart mom.

Smart mama bear.

And so this last year into this year, she has four cubs, which is extremely unlikely.

Yeah.

And, but they're all thriving. Like, and that's what I'm saying. She is, let me see what the count was.

She's like a, when I say successful mom, I mean successful mom. And let's see here.

I bet they also take advantage of the roadkill too, because I know they're scavengers, so mine as well.

So yeah, so born in 96, she typically sticks around Grand Teton National Park. Okay, so she has had, successfully reared 16 cubs and grand cubs. So.

That's, yeah, that's really good for a mama bear.

I mean, typically it's like, you know, they might have two cubs, maybe three.

Mm-hmm, so 16 total. She's doing a hell of a good job. And again, unfortunately though, because she does tend to stick to road sides, there is obviously human interaction.

Not murdered. But, well actually one was murdered. One was illegally poached, one of her cubs.

But I believe it was an adult by the time it was killed. But that guy was charged. But she actually did at one point maul a hiker in a park.

But the hiker and the hiker's family was like, you need to take care of this bear. But the park superintendent was like, I mean, she's doing what-

But she's a mother bear in the wild.

Yeah, she's a mother bear in the wild. She's kinda doing what she was supposed to do in that situation. Like-

Dude, good for him.

Yeah, like you are out here, you hike. Like, this is a danger.

You accept the risks.

Yeah, you accept the risks.

That's like suing nature.

You don't get to do that. Yeah, God, let's not start suing nature. So anyway, so the big hype around grizzly bear 399 this year is because so many of her cubs have had negative encounters with humans.

She tends to stick around the roadways. I mean, wildlife photographers follow her out the wazoo. Typically, if you're gonna see like really, really good grizzly bear pictures, if it's not coming from Alaska, I can almost guarantee it's her because she's gorgeous, like super photogenic.

I mean, in one that kicks out like more than two cubs, like, I mean, come on, that's perfect, perfect for pictures.

And access, right?

Yes.

Easily accessible.

Easily accessible. But the big news is because she has been getting so close, more and more people have been pushing for her to be taken care of, AKA.

And so they, she was in Jackson Hole, Wyoming, cause they're, you know, Grand Tetons. So she was in Jackson and just like going for strolls through the town, like she wasn't becoming a menace at all. Like, and that's what's funny is like she's, at least from what I have been able to find, she's genuinely like not causing problems like normal bears would.

She's just like going through a stroll through the city because to her that's safe because male bears aren't there. And so she's keeping her cubs safe by sticking to these areas. But the big news is because so many people are like, listen, she needs dealt with, she's in the city, she needs killed, like take care of her cubs, whatever, move them, get rid of them.

Without doing any of that, they successfully scooted them way north of the town up into hopefully an area where she's gonna stay. But I don't know, every year, she kind of just like moves around. But this year, she was like way, way, way out of her normal zone anyway from what she typically was because she did spend part of her year in the national park and she normally hibernates there too.

It's just she's gone like way outside of her comfort zone this time. So anyway.

Mary, she's avoiding an ex.

Right, right, just stay away. Stay away, I don't like that one. So, but, so now she, for now she's successfully moved far enough north that they feel like she's not gonna be encountering any humans.

But then again, I mean, she's purposely staying close to humans.

Right, she's like, well.

Yeah, so we'll see. But Department of the...

Actually, it ends well for her and...

Yeah, and I mean, dang, I mean, that's just so many cubs and the Department of the Interior, like it was a huge partnership to make that happen. So many people were involved with that. And it, yeah, it's just definitely a group effort to get her moved because she was starting to cause problems without intentionally causing problems, like mobs of traffic, just trying to get pictures of her and all kinds of stuff.

But I mean, when you're a 26-year-old bear, you're that successful and you're that cute and photogenic and just like walking through downtown Jackson, like it's kind of hard to not cause a crowd and a ruckus, just because she is like famous. I mean, she has her own Facebook page, she has her own Twitter account at one point. I don't think it's active anymore.

But yeah, so that was the news. Grizzly Bear 399 should be.

Save 399.

Yeah, save 399. We'll put that along with the, what were we going to save? The tiny raccoons?

Pygmy raccoons.

Pygmy raccoons, which I really think we need to make a campaign for. Save the pygmy raccoons.

The stories, the awareness that they even exist.

Step one, let people know they exist.

And everyone can get on board with a tiny raccoon. Pygmy raccoon. I challenge you to find someone who doesn't think.

It's the tiny hands. It's the tiny hands. Yeah, gosh.

All right, so we're going to talk about plant defenses. And just in general, just some cool things that Laura and I have talked about or have found. So plants, Laura and I, I feel like definitely we have a love-hate relationship with plants.

As much as I love trees, this episode reiterated why I hated my botany class. Now, to specify, I loved my botany class when I was in Australia. I hated my botany class when I was an undergrad.

I mean, come on, who's not going to love a botany class in Australia? Yeah, it was a field botany class. Well, that wasn't the only difference.

The professors, because I had a hilarious professor from my Australia class who is a world-renowned botanist and really cool at what he does. Originally from Germany, married a Fijian.

Oh yeah, he said he had a whole bunch of accents.

Yeah, because he was raised in Germany. Then he lived in Fiji for a long time, married his wife, and then they moved to Australia. So his accent was all kinds of interesting, but he was hilarious and still publishes, still writes a lot, still does a lot of research.

Gunnar Kempel, so awesome, shout out Gunnar, if he ever finds and listens to this. He's hilarious. We introduced him to the American s'mores, the dessert s'mores.

He's never...

I'm sure.

Oh, it was, because he had a huge sweet tooth, so that was fun. So super smart guy, but I loved learning botany in Australia because it was practical, and it was just really fun, but learning it from a textbook, uh-uh. And so I feel like this was almost too textbook research for me for this one a little bit, but I tried to keep it interesting.

Man, this would be a really... I mean, if you didn't want to do this textbook, we could just go out and try out these to see what happens.

Listen, I...

But I don't want to do that.

I don't, and I'll... My first one, you'll find out. So do you want to go ahead and start then?

I think so. So like Katy said, we're going to talk about how plants have come up with some incredible different ways to prevent themselves from being eaten, for the most part, among other ways to defend themselves. And sometimes those defenses have even turned pretty much weaponized, at least in my case.

So I'm going to start out with my most extreme one, I think. Yes. So the plant defense that I'm going to focus on is called...

They have things that are called idioblasts. Which is a cool name.

It is, but I'm having twitches of flashbacks to...

So it means crazy cells.

I mean...

Which is true, because what they are are specialized cells in a plant that are different from ones around it. There are several different groups of them based on their functions. And I'm going to tell you about a couple of these different functions.

All of them are intense. So some idioblasts contain bifurin cells. And so if you break them down, it means two doors.

So the cells, they're shaped like ovals, and they've got two openings, one on each end. Inside of those are these crystals of calcium oxalate. So think...

And they can be in lots of different shapes. They can be in prisms, they can be in needles, they can be in like a star shape, almost. Really hard, of course, because they're crystals.

And so what happens is, if an animal bites into that area, the cell breaks and the crystals shoot out, which are extremely painful and irritating, in the mouth of whoever just bit that. Yeah. So just imagine, like, basically biting onto broken glass, essentially.

Which is intense. So some of these crystals even have barbs or grooves on them to inflict maximum damage or channel toxins.

Evolution was like, let's kick it up a notch.

Yeah, yeah, yeah. It's gonna hurt a lot, but you know what? Let's make it even worse.

Yeah, let's make it worse.

And these crystals can be toxic in large enough amounts. Like, if you eat a giant mouthful of essentially broken glass, it can do some serious damage.

Well, yeah, because it's not even the initial cut, it's also the infections that could come after it.

Yeah, and it can cause swelling, like in your throat, and all kinds of things. Yeah, and that's just one type of idioblasts. Some of them contain pain-inducing chemicals that are also ejected when bitten, and that's the case for stinging nettles.

Which I'm going to go into that. I'm going to go into that, yeah. We always overlap.

Just enough.

Yeah, just a teeny.

Just enough.

A few take it to the next level by injecting, so not just pain-inducing chemicals, but they're called pro, hold on, prostaglandins, which are hormones that actually amplify pain receptors to make it as painful as possible. It's not just going to hurt.

It's really going to hurt. Again, again, evolution. Let's just make this a little more painful than what it needs to be.

Some idioblasts have bitter-tasting chemicals, like tannins, which is what you find in red wine, and a lot of people are actually allergic to tannins, or they get really red. I know some people that have to like, yeah, can't drink red wine because of that. Some have weirdly shaped cells with super thick secondary walls, which make them hard to chew, so much so that they wear down the animal's teeth if they're constantly chewed on.

Oh my gosh.

And that's an example of pear skin. And I was like, what? Pear skin?

Pear skin?

I thought pear skin was pretty thin, but I guess like a wild pear? Yeah, they've got these really hard cells that will wear it down.

I wonder, yeah, I was gonna say, that's what you brought up a good point, because you said wild pears. And so I wonder if we've softened this. I wonder if we've softened the skin over the years.

Or thinned the skin. Probably, probably. Finally, some of them contain silica cells, which silica, again, like broken glass, but that silica is specifically found in things like grasses and sedges, and gives them a little bit of extra protection.

So what plants can you find these idioblasts in? Tons of different kinds. Succulents, the onion family, mulberries, stone fruit, roses, grapes, and beans.

So, I mean, you're probably thinking, well, Laura, a lot of those are food that we eat, and I can eat them just fine. Well, yeah, but we're also pretty big animals, and we've also domesticated a lot of these things, so we probably did change them to become more edible. But then there are some that are just straight up jerk plants.

For example, Diffinbachia. This is a very common house plant.

Diffinbachia?

Yeah. At least I'm pretty sure that's how you say it, or Diffinbachia. Kim actually has it at home.

Really?

It's a very common house plant.

So it can tell you...

Listen to this. So it's also, its common name is Dumb Cane.

Yes. Yes.

Which Kim thought, because it's such a pain in the butt to take care of and keep alive.

Could be.

And Kim says she has named hers Herman. Herman Cane. Thankfully.

Thank you, Kim. But the real reason it's called Dumb Cane is because it has idioblasts that will shoot both sharp crystals into your mouth, as well as a chemical similar to reptile venom. It causes paralysis in that area and leads to temporary loss of speech, which is why it's called Dumb Cane.

What? Because it will just make your mouth so numb you can't even talk.

Man, that's like one of those ones that needs to come with so many house plants.

Oh, yeah. People do not understand that.

Yeah, they don't know.

Yeah.

They just buy them and they're like, oh, this will be fine. I think they'd need much larger warning labels on them.

Agreed. Another one that's a pretty common house plant is philodendron, which contains lots of crystals that cause swelling and choking if ingested. Like, you know, and like the elephant ears that you see everywhere decoratively definitely will cut the crap out of your mouth if you eat it, ate it, and can be very dangerous for pets and children.

Yeah. So is this an effective plant defense?

Heck yes.

They're freaking weaponized. You are chewing on broken glass. I would absolutely avoid it.

Plus, the plants can use the crystals for both stability and calcium storage. So it's not just a defense. They also found out some other ways to use it.

But dag on, idioblasts will mess you up.

I'll say. Dang. Well, I'm glad you brought up stinging nettles because that's actually the first plant defense that I'm going to talk about.

So, let's see here. And I have had firsthand experience with this one. Me too.

So, well, I've had it. I'll get into it. So before I get into the details of my specific stinging tree itself, let me first talk about trichomes.

So this is my botany flashback. I twitch for the day.

Technical name for this.

Yes, so trichomes are what gives the plant the sting, essentially. So a lot of plants have trichomes, but they do not sting. Trichomes are basically just a type of plant hair that are a single layer of cells on the outermost area of a plant that can cover the leaves, flowers, roots, and stems of the plant, basically anywhere.

If you've seen a hairy plant, trichomes. It's not a hair, trichomes. Fun fact.

So let's see. And Luke, I think I was even talking to my son, and I was looking up research for this one. And he's like, I've seen a hairy plant in the backyard.

And I was like, yeah, buddy.

Sure.

I was like, they're everywhere.

Yeah. Even like some of those little flowers that grow. Like those little flowers.

Yeah.

But if you Google trichomes, holy moly, all that comes up is a bunch of info on cannabis plants. Why?

Really? I didn't know. I never thought about them being hairy.

Well, technically, they are because trichomes are the part of the cannabis plant that holds all the good stuff, basically. And so this shows like the drastic functions that trichomes can have because they can either, as a defense, trichomes can serve to either protect the plant from, let's say, like small herbivores eating the plant, sometimes even larger herbivores on the more rigid trichomes, which is a little bit more similar to like what you were talking about. They're not necessarily thorns, but they are like more rigid hairs.

But trichomes can also help keep frost away from plants from like the more sensitive living tissue. And even in windy locations, it can break up the airflow across the plant surface.

That's pretty smart.

Trichomes can reflect the sunlight in dry or hot environments, among several other things. So, as you can see, trichomes, the hair on the plant, or what looks like hair to us, are extremely diverse in defense mechanisms for what, depending on what plant they are, what environment they are in, et cetera. The one I'm specifically now going to focus on is this stinging tree called Gimby Gimby, which is in Australia.

Of course.

Mine was just stinging nettles, plain old stinging nettles from America.

No. This is brutal. Yeah.

This is the worst. So Gimby Gimby or Dendroxine morodides, more-o-r-id-i, more-i-dees, more-i-dees.

Sure.

Gimby Gimby is found in my most talked about area of the world, Australia. More narrowed down, it's found in Northern Queensland and where I spent most of my time. Whenever I was in Australia, the Atherton Tablelands, which, side note, gorgeous, gorgeous area.

If you just Google Atherton Tablelands, A-T-H-E-R-T-O-N, you'll be, Tablelands, you'll be blown away. Anyway, so Gimby Gimby is found here outside of Cairns, far northeastern Australia. It's a member of the Nettle family and one of four stinging trees in the Nettle family found in Australia.

It's more widely known as having the most painful sting which has made people go mad and even unalive themselves. So trigger warning for later on if you want to skip ahead past this section of the episode. Obviously not going to go into details, but I do go into a little bit more of the side effects and how people have taken their lives over this.

So skip over it a few minutes if you don't want to listen to that part. So Gimby Gimby is named after the Australian town of Gimby, a gold mining hub founded in the 1860s. And you can find the plant, though, in rainforest clearings as well as along creek lines and other clearings, you know, where people tend to walk.

So of course, this plant can grow upwards of 10 feet tall, and the stinging part is found in the trichomes, the tiny hairs I talked about, which are found all over the leaves and stems, and you know, since the universe has a sick sense of humor, the leaves are all in the shape of hearts. So yeah, absolutely perfect. So you know, this is touched by every unknowing tourist out there going aww as they reach for it.

Oh, right. And especially since these cute, you know, heart shaped leaves can be as small as your thumbnail or up to about a foot in length. So yeah, so it's basically the perfect size range for people to think like, oh, about how, oh, how cute this tiny little heart I found was, or, oh, look how great, cute this giant heart is.

And whammo. Grab it. Affected.

So when something touches the hairs on these enticing heart shaped leaves, or even brushes up against the stems, the there's a bulb at the top of that hair which sticks to the skin and releases a neurotoxin.

So that's where my idioblast comes. Your trichome is like the structure, mine's the pumping out of the toxin.

So break down neurotoxin. It's a toxin that when it enters the body affects the nervous system. So what does this thing feel like?

Again, trigger warning for what's coming up. So first, you will feel burning sensation. So far, not bad.

But you'll reach peak pain in about 20 to 30 minutes. And even if you make it past the most painful part, which most people do, of course, because you're like, ah, 20, 30 minutes, not so bad, the hair can remain in your skin for up to six months.

Oh, my gosh.

Which means at any time something brushes against that part of the skin in which you've been stung, it resurfaces the pain.

So your hands? Anything. And I know, but let's say you grab that leaf.

Yes.

Then we'll be grabbing things.

All the time.

Yes.

So, and okay, so, so.

It's not like a random body part.

Correct. And it's like if you have water brush around it, hot or cold, doesn't matter. You know, you would think cool water would help, doesn't.

It only helps to resurface the pain. Not only is it painful where the hairs are on your skin, but the toxin will make your lymph nodes swell, and the pain where the lymph nodes are will last an additional one to four hours after something brushes against it. So the pain from these hairs have been said...

Okay, so first burning can make your lymph nodes swell, and all of that combined has said to feel like a constant either razor blade cuts, being stabbed with hypodermic needles, and overall several people have described it as pouring acid on you while being electrocuted at the same time. Yes. So because of this ongoing pain for up to six months, this is when people have unalived themselves over just over the constant pain of can't get away.

There have been reports too of horses and dogs that have brushed against it, and they just die a few hours later. Like, so whether they're more susceptible to the pain, or they're just like, I'm done, and they decide to, cause you know, they can't take their own life, but whatever it is, I couldn't find much more if they're like more susceptible to the pain, and they like succumb to that or what. But, I mean, just think about trying not to brush, like let's say you got it on your arm, okay?

You try not to brush up against something, you accidentally do, oh my gosh, excruciating pain for four plus hours, that whole time you have to not hit it again on against anything, or it starts to clock all over. Correct, or else it starts all over again, so you can't put a cold compress on it, nothing.

Dude, skin graft, that's...

Right, just cut it out. So, let's just go, okay, and it doesn't even end there, doesn't even end there. So let's just say you're gonna go for a hike in the beautiful Atherton tablelands, and you're like, okay, don't touch any heart-shaped leaves, got it.

Does this matter? No. It's freaking Australia, so of course it doesn't matter, because these hairs can be airborne.

So even if you're in the general area of these plants, you can still have one of these hairs cause major damage.

So never visit the Atherton tablelands, which you're telling me.

And it is such a gorgeous, gorgeous place. So is there an antidote for it? Is there anything you can do?

Also, no.

Oh my gosh.

So most powerful form of protection against these plants is basically just to wear long layers. And when you're done in the bush, immediately wash them, which is what we were told to do. Anytime we were out surveying, it was like head to toe, just have on long layers.

Like you can wear light layers. Doesn't have to be, need to be very thick, but you have to wear layers.

That's a good rule for the jungle in general.

Yeah, it really is. If you wear shorts like myself did, cause I'm an idiot, I also wore gators, but that was mostly because of the snakes. I was more worried about, like I wore gators to watch for snakes, not, you know, gimby, gimby, which we were told about because the research center that I was staying at, and when I say research center, it was like a small building with four rooms on like a hundred hectares or so of land.

But one of the employees there was stung by the plant, and he was just telling us like the, he was like the maintenance, like facility upkeep of the whole place. And he was telling us like the horror story of what he went through because he had to remove it from an area or something, I think is how it started. And like no matter what he tried, because those hairs can just like flick off and then just go airborne.

Man, he, because he had it on his forearm. And so he was like, no matter what he did, and you can't go in and like, because they're such tiny hairs, you can't really like, well, not even just the hair, it's in those, the bulbs that get stuck in your skin. It's not like you can go in and remove those, because once it releases the neurotoxin, it's like in your system.

And so like the hairs are stuck in your arm. You can't just go like tweezers and like pick those out. Like it's, there's just nothing that you can do really.

Too bad we can't like vacuum them out. So at least you won't have to do with it for six months.

Right.

Just have like a suction.

Maybe Australians are just that badass that they're just like, I don't know.

Six months of pain, no big deal.

Yeah, whatever. So even with all these, you know, this defense mechanism to the extreme, there is a species of beetle and the red-legged patty melon, which is basically a tiny wallaby, which are so freaking adorable.

Patty melons.

Yeah, they're adorable. They can eat them. Like, they can eat these plants, and nobody really knows if the patty melon is immune to the toxin or if they too are just badasses, that they just are like, whatever.

Like, they just don't care. They have to be immune to the toxin. Yeah, they just have to be immune to the toxin, but they don't really know why they haven't been studied.

I mean, to be fair, this species of patty melon, like, we did surveys for them all the time to try and see, and we did have a few on the property, but they are extremely endangered. And so even just trying to find enough of them to do a sizable study on it is slim to nail. So the Gimbi Gimbi plant, incredible plant defense mechanism for the plant, like hell on earth for humans, though.

Craziness.

That, it's very, you're right, it's very similar to mine, but in a different, like, yours is the toxin, and mine's how it gets there. That's crazy. Or no, yours is how it gets there, and mine's the, yeah.

Yeah. Whoa.

Oh, man. Okay, well, let's take it down a notch, and rather than being like a weaponized defense, my next one is just that some plants play dead.

Extreme opposite. Some are throwing spear hairs at you, and others just are like, leave me alone, please.

Yeah. So, you know, listeners out there might think that only animals, like, you know, opossums and stuff can play dead, but some plants do too. So when they're touched, the leaves close and the branches droop, so the plant looks wilted or dead, and then perks up a few minutes later, which is kind of cute.

So how does this work? It's a little sciency, but to break down, reaction is stimulated by a couple of things. It could be that the plant is touched.

It could be that it had heat blown on it, wind, or even light change. These plants usually tend to close at night, so light changes. So normally, the water in cells of a plant are turgid, which I do love that word.

Turgid. Turgid. And so it holds everything rigid.

So turgid, rigid. The movement is due to a rapid release of water from the base of the leaflets, which are like, you know, you're looking at a leaf that looks feathery.

Okay.

These ones do. There's tiny little leaves that are leaflets that then make up a leaf with a stalk. So water comes out of the bottom of the leaflets and the leaf stalks through osmosis.

So things moving from one part of a cell to another that then leaves those leaves flaccid. Also a great word. So basically, the plant peas itself when it gets scared, and then everything goes flat.

Poor plant.

They're just like, ah, ah! That's how you release the water. It's so fast.

This reaction happens in four to five seconds. So, I mean, it's not like a...

Yeah, for a plant, that's quick too.

And boom, yeah, whereas unfolding can take up to 10 minutes. So, you know, it's cautious. And actually, it's believed that the time that it takes for it to unfold, like how long it takes, is actually the result of behavioral adjustments that it makes to different stimuli.

So, like, for example, a lot of plant eaters like young tender leaves, so in a study, when these younger leaves were repeatedly exposed to, like, non-damaging stimuli, they would consistently fold completely, but they decreased the time it took them to unfold. Like, they were like, oh, this isn't actually scary. Like, this isn't a problem.

Didn't we talk about this on another one, too?

Yes.

Where it's like they're learning.

Yes, this was on our learning plant one, because this is the mimosa, which we brought up and was done in that study.

Okay, I thought so.

That woman who was dropping them.

Yes, yes, yes, yes, yes.

So this is the mimosa pudica, aka the zombie plant, aka sensitive plant, aka shame plant, aka humble plant.

I like how it's shame, and then it was like, you know what, that's kind of mean.

Humble plant. Humble or sensitive. It's just sensitive.

I'd say most people know this as sensitive plant, but if you look it up, most hits, you'll get a zombie plant. They're sold as zombie plants because they die, like play dead and come back to life.

Yeah, which I mean, let's be fair, you're not going to be selling many humble plants. You know what I mean?

Putica means shy or bashful or shrinking in Latin. The mimosa is a lot of us, they're an ornamental tree. They're not here in the United States natively, but they've got really tiny feathery looking leaves and little pink puffball flowers.

We might have a type of mimosa that's native to here, but I don't think mimosa putica is from.

In the Northeast? Or just in the US in general?

I don't think it's in the US in general. I think it might be an Asian plant, but I should have looked it up.

Oh, interesting.

But I didn't. Sorry, listeners.

They can look it up.

Is this so? Is this an effective plant defense? I mean, yeah, I'd say so.

There's a couple of different theories here as to why they do it. One, it could deter predators because it appears dead, and they're like, well, I'm not going to eat a wilted dead plant that is not very nutritious. Or that it could startle them with the sudden movement, like say a rabbit bends down to like nibble on this thing.

All of a sudden leaves move. The rabbit's like, ah, because who knows what could be in there? Because Mimosa pudica is not like a tree.

There are other types of mimosas that are like taller. This is like ground cover almost. It's like a foot tall.

OK, OK, OK.

Highly browsed upon by. So it is like got extreme reactions. They think the movement might also shake off harmful insects.

So if it feels a little pitter patter of insect feet, leaves close, insect falls down. They also by folding the leaves, you know, they're smaller. They present less surface area to be nibbled on.

And they also have little tiny spines all along their stems. So when the leaves close, it exposes the spines. So, yeah, plus it can actually help the plant from losing water, have protection overnight, or reduce physical damage, since, you know, it reacts to like heat and wind and light.

So it's not just like a predator defense. It's also for some other things. So, yeah, playing dead, it works for animals and it works for some plants.

Huh. See, in the learning thing, is that...

Love it.

And again, yours feeds directly into what I'm going to talk about.

Yes, love it.

We didn't plan these, I swear. Kim just reads over it, and we were both worried that this one was going to have too much overlap because of how similar things are. But it's meshing perfectly.

All right, so the second plant defense mechanism I'm going to talk about is carnivorous plants, and in particular, sundew. Yes. So first off, what is a carnivorous plant?

Well, carnivorous plants are ones like Venus flytraps, which are native to North and South America. Good grief. North and South Carolina, here in the US believe it or not, they don't largely rely on, well, carnivorous plants, the whole point of them is they don't rely on photosynthesis or the soil to gain a lot of nutrients.

So they, because they normally live in very poor nutritious soils, like bobs and things like that. So to get all that nutrition, they have a variety of ways to capture, digest small invertebrates, or any, well, a lot of different invertebrates, I should say, and small invertebrates even, like not here in the US but...

Or small vertebrates.

Yes, any invertebrates and small vertebrates. But there are some pitcher plants abroad that can ingest, well, they don't like attack small mice, but the small mice or frogs, yeah, will fall in, and that's a nice treat and very nutritious for them. So, I mean, it works.

So while coniferous plants themselves, they do that for nutrition, there is one plant, the sundew, which I'm going to talk about, that developed a defense, which then apparently might have figured out how helpful it is as a defense mechanism and turned it into nutrition. So bear with me here. So sundews are the largest group of carnivorous plants.

There's a lot of different types. Sundews are often called flypaper plants because they trap prey in the sticky hairs on their leaves.

I've found there actually was some growing on a lake near my house.

Really?

Yeah, it was real cool. They were in the sphagnum moss, which I think has something to do with poor soil conditions.

That's what I was just going to say. If you see them, then clearly it's poor soil where they are. So the sticky hairs on the leaves, like with my last plant, these are trichomes which protrude from their leaves, and each trichome has a sticky gland on the tip.

These droplets of stickiness look like dew, which is where their name comes from, sundew plants. The glands of the sundew plant produce nectar to attract the prey. There's a powerful adhesive to trap it, and the enzymes then digest it.

Once an insect becomes stuck in the adhesive, very similar to Laura's, the nearby trichomes will coil around it, it's a physical reaction, around the insect and smother it. And the insect can be quite large since sundews can reach a height of up to 10 inches. Yeah, the sundews, these caped sundews, I should say.

Super cool.

Or all sundews. Some sundew species are tall and vine-like in appearance, while others, similar to yours, hug the ground, making their size just very variable.

Yeah.

So let's talk a little bit about then what I was hinting towards earlier, their move from defense to carnivorous. So we think defense came first, which then carnivorous came after. So, like the animal nervous system, plants can use electrical signals to carry messages over long distances, helping them to mount pretty much like a rapid response to wounding, infection, or an attack from an herbivore.

So instead of traveling along nerves, like with animals, which plants don't have nerves, plants' electrical signals are believed to travel through the xylem and phylum vascular tissues, which tells plants to activate the wound response. The wounded plants would curl up in self-defense. Normally, a movement alone, like Laura was saying, would scare an animal away because plants aren't supposed to move like that, and animals know that.

Over time, scientists believe that this movement, the plants somehow figure it out, oh, hey, this is useful, and the wounded plants normally accumulate higher levels of something called jasmineets on the leaves, which led to an increase in digestive enzyme production.

I just love that these little plants were like, okay, I'm protecting myself, and then a couple of them were like, well, come on, let's not waste this opportunity.

Exactly.

They were conservationists, as well.

Yes, right. Let's jump ahead of this here. So, and I mean, it might have been like they had that, well, anyway, I don't want to skip ahead of myself.

So between the movement and the increase and showing the increase of digestive enzymes already being there, I feel like they were maybe already adapted to get to the carnivore stage and didn't realize it. Or, you know what I mean? Or just like, I don't know, just happened in one day, and they're like, oh, this is handy.

But having these enzymes provides direct evidence that carnivorous plants and plant defense are evolutionary, like, related mechanisms. And it just happened to be, yeah, this one just went in a different direction. So since they are so similar in function and response, one could raise the question of, well, how do we know it's carnivorous and not still just a random defense mechanism that happens to capture insects, you know what I mean, like, over time?

Or there's like several other questions that can be asked about these plants now, too. There was a study done by Kretzko et al. that suggests that the electrical signals in jasmine, remember the digestive enzyme stuff, spreading throughout wounded plants can trigger a false alarm, but the sundew quickly recognizes the localized pattern of electrical signaling and jasmine accumulation in combination with chemicals normally released by a prey, causing it to ramp up its secretion of digestive enzymes in the carnivorous response at the appropriate place.

So, somehow...

Yeah, I'm like, right, where they're without brains.

Without brains. It knows when, even though it's a chemical response, it knows that when it has a prey versus when it doesn't. So if something just like fell onto it, it's gonna still have that response, but it's not like mechanical.

Like, we've thought about plants for so long where as soon as it falls, boom, it's just a reaction, and then it's like stuck there until it completes the quote unquote process. No, if it recoils and it realizes it doesn't have a prey, it releases and all those extra digestive enzymes are never released. But if it has a prey, it knows it has the prey, and it will start to release way more digestive enzymes.

Again, this goes all back to the fact of that plants, I just really think we're eventually going to get to a point where we're like, wow, we've just been looking at this all wrong just because plants aren't as quote unquote alive in the same way as what typical animals are. They are well aware of some crazy crap that's going on. So, anyway, so yeah, so defense mechanism first, which then turned out to be a really good adaptation and turned these plants into carnivorous when I guess maybe the soil that they used to live in was nutritious and then it started to not be as nutritious and it just adapted.

They don't really know.

But I guess people say the best defense is an offense, right? Like, isn't that the same?

It can be, I think so.

For a second, I was questioning myself, did I get flip flopped? No, I'm almost positive the best defense is an offense. And that's what carnivorous plants did.

They were like, you know what? Screw just defending. I'm also going to attack.

Yeah, right.

Okay, my last one that many of us are actually familiar with, you just might not know it, is the plant defense called capsaicin. So what is capsaicin? It is a chemical that makes plants taste spicy.

Which I love. Yeah, and I don't. And so we're going to talk about that.

I am 100% okay with pain when I eat, as long as it's tasty.

Gotcha. So capsaicin is kind of oily in nature in the fact that it doesn't mix with water, and it can be measured in Scoville heat units. Okay, so how does capsaicin work?

It is produced in plant tissues and things like that, and has its highest concentration in the white stuff that surrounds the seeds called the pith. So mammals, and probably insects, but definitely mammals, have special taste receptor channels. So this, again, sorry, this is getting kind of sciencey and technical, but I mean, that's what our listeners are here for, so.

Right. So they have special taste receptor channels called TRP channels, transient receptor potential channels. When capsaicin binds to those, it triggers calcium ions to go into a neuron.

The neuron gets agitated, results in burning. So capsaicin binds to pain receptors that usually react to heat. That's why we feel it as burning, because so there is no there is no taste bud for spice.

There are taste buds for sweet. There are things like that. Spice is not a taste bud.

Spice is a pain receptor.

So I have no pain receptors.

Yeah. And so which which so which I will talk about, but that probably means that that gives you the ability to actually taste. Your other taste buds are using the other parts of the plant.

It's only the pain receptors who are like, I feel no pain.

So the reason why you might enjoy it is one of two reasons. One, these pain receptors can be destroyed through long exposure.

That's very likely.

So the more spice you eat, the less spicy things will taste because you're desensitizing them. Like it's the paint, the calcium ions that are constantly flooding these neurons. Eventually, they're like, I can't, and they stop.

I can't.

You've given me too much, Katy.

I'm done. You've either killed or exhausted your pain receptors, which since these are pain receptors that identify heat, do you, I just thought about this, do you like to eat really hot? Like does hot food bother you?

Not really. I mean, I don't like scolding hot food, but not as much. But I am, I was going to say, I am the person that can and will take a scolding hot shower.

Oh, me too, for sure. And so that's what's interesting because I can eat, like, let's say I pull a pizza out of the oven. My husband has to wait at least 10 minutes before he can eat it.

Meanwhile, I'm devouring it.

Yeah. But you can't, it doesn't affect you, but you also can do spicy.

You can't have spicy food. So, I don't know, my pain receptors are selective or something. The other reason why maybe you can eat spicy food is because mutations within that receptor are genetic.

That's what I was going to say. I think it's more genetic.

That's why certain cultures are more able to deal with spice than other cultures.

And I am very white and very German, and they typically... But I said the genetic thing because my brother and my dad, before he passed, we all could do... And my brother and I can still, both of us, like spicy food.

And for me...

Your dad had a mutation and gave it to you guys.

Because for me, it started as a kid. It was purely competition between my brother and I. And it never affected me as much, but if he ate something spicy, and he was like, you can't do it, it immediately turned into a competition.

So it definitely was a little bit of over time. But at the same time, I feel like it didn't affect me. It never has affected me as much as other people.

Spice does.

So that's kind of how capsaicin works. It's found in chili plants. And there's all different kinds of chili plants.

And interestingly enough, so scientists have found that spice levels increase in wild chili peppers, growing in areas with more fungus-carrying insects.

Interesting.

So the reason for that is because I found out quite a bit about chilies and things like that. Do research for this. So wild chilies apparently are really no bigger than usually like your nail on your finger.

They're really tiny, and they're basically all skin and seeds. So when things bite them, it's like guaranteed spiciness.

Yeah. Which makes sense.

The fungus-carrying insect thing is because so capsaicin is actually also prevents microbial growth. It doesn't. The chemical doesn't let fungi and stuff grow on it.

However, if it doesn't have very much capsaicin in the plant, when these little insects come along and make puncture marks in it sucking out the juices, if they happen to have some fungus on them, then the fungus gets into the plant, and it's kryptonite. It cannot handle fungi. So it increases its level of capsaicin to be able to combat that, because the capsaicin can prevent the fungi, but it has to have enough to do that.

Man, that's really cool, though. Yeah, it's a really cool relationship. So is it effective?

Yes. That's one example of how it's effective. So it also keeps the insects away because it tastes spicy, and it prevents the fungi and other microbes from growing on it because of the capsaicin, so it's like a double-edged sword.

Mammals are also vulnerable to capsaicin, as I said. It's in our taste receptors or our pain receptors, so most mammals avoid chilies. This keeps the fruit from being eaten and their seeds destroyed, especially by rodents, because a lot of the rodents will just eat the seed around and it won't be able to germinate.

On the flip side, this is not at all a problem for birds as they are immune to spiciness.

Interesting.

Which I did not know.

No, I didn't know that either.

They lack this pain receptor, so they can eat as many chilies as they want. No problemo. And that's what the chili wants, because the birds are their seed dispersers.

Gotcha. Which makes sense.

Which is why chilies are also brightly colored, because they're attracting birds like a berry.

That makes sense.

Because really chilies are just a berry.

And it's native form. It's just a chili. Like it's small.

It's just a berry.

A little berry. So it's just funny that as humans, we're just like, you know what? I don't care.

I don't care. It might hurt. I'm going to eat it anyway.

Yeah, right. And let's make it bigger and spicier.

And that's kind of so. Fun fact is that chilies were one of the earliest domesticated crops in the New World. So chilies are from South America.

They were domesticated 6,000 years ago by people. Probably because they prevent food from spoiling. So it wasn't necessarily that the people were like, yes, I like that this is spicy.

It was just if this food isn't spicy, I'm probably going to die from microbes. Yeah, which because they're living in the tropics.

Yeah, right.

Spicy food is especially important. And you will see in other parts. So the chilies got then taken to other parts of the world and became very popular.

Spicy food is especially popular in tropical areas.

Which, yeah, I guess that would make sense, and that's why.

Right, to prevent food from spoiling.

Fascinating.

Yeah, never thought about that. And so we domesticated the chili, and we actually made it much less spicy, even though we've made it bigger. And there are some that we've, you know, tweaked and stuff to make like ridiculous.

But wild chilies are almost always more spicy than domesticated chilies. And humans have actually found out that we can use capsaicin as a topical cream for arthritis and psoriasis, because it is making those pain receptors flood, flood, flood until they numb. And so it is causing numbing of the skin.

Interesting. So it's a great defense to keep things away, except for people because we're crazy in gluttonous performance. Except for me, who literally cannot eat more than nacho cheese.

As soon as my tongue starts burning, the fun is over.

You're done.

I think that was you I was talking about before. I have asked, what can you taste? Because I literally taste nothing.

It's like I have put my tongue on a hot plate. There's no taste. It's only pain.

So why would I continue eating?

Yeah, I taste flavor. And there is some, I'm not going to start naming and bashing restaurant names, but there are some restaurants that will give out hot wings and stuff like that. It is just hot, painful hot, because it just doesn't taste good.

It's just cheap sauce. There's a fantastic show I'll just plug in. I'm sure we'll never get on it, but it's called Hot Ones.

Oh, yes.

And he interviews people while eating hot wings.

A friend of mine was telling me about that, and I haven't watched it yet.

It's so good, so good. But some of those hot sauces are made with extracts, and the extracts are garbagey, just painful, no flavor. Whereas the actual chilies do have a taste if you've got the right kind of receptor.

And that's like for me, I love trying different types of very spicy curries, just because to me, it's so flavorful, and you can do so much with different curries. But yeah, I taste more of the flavor behind it than the pain, and there is a right and a wrong way to have spice. And I think a lot of the chain wing places, sometimes, and they put too much emphasis on the hot of it, that it doesn't taste good, and that I don't like, because then it just doesn't even taste.

Because I think a lot of it is just for novel.

Exactly.

I think a lot of it has to do with ego. Like, you see that Burger King right now has ghost pepper poppers, and you're like, okay, this is just to say you have eaten ghost peppers. At this point, it's just a bragging, right?

Yeah.

Nobody enjoys eating them. You're a liar. And, you know, because it actually, it's a chemical that destroys microbial growth.

It's doing something to your insides.

It's doing a lot of cleaning. It's just not causing microbes. Oh, goodness.

That was interesting. I like, I didn't know. I didn't know.

Well, I guess I should say I didn't know. I never thought about the movement and why spicy foods would have been, you know, in more tropical regions. That's really interesting.

Yeah, right. I knew a little bit about all of these defenses, but nothing more than superficial. So I liked finding out a little bit more.

And just that plants are crazy, as I've always known. But like, dang.

As much as I don't like going into the deep botany of it, it does just blow my mind every time we talk about plants, because how we don't just say that they're alive, just a different type of alive, beyond me.

Yeah.

Beyond me. Well, folks, plant defenses, hopefully you guys learned something. I mean, I know I did, just researching it.

And next week, guys, you should be so excited for our episode. We have guest speakers on. They are going to talk about their specialties and actually battle out who has the best study area.

Field of study, yeah.

Yeah. So definitely tune in next week. We're almost finished the season.

We only have two episodes left.

And then season four will be right around the corner with the new year, and that will mark not only beginning of season four, but our one year anniversary, which is also crazy to think about, but somehow we've managed in our hectic lives to keep this going for a year by the skin of our teeth at times. Right? With thousands of downloads in 30 plus countries.

So thank you guys all for listening and for support and continue to do so. And until next week, we will hopefully hear from you over on social media at FTLON Podcast, or just shoot Laura and I a message.

Tune in next week.