The Saguaro, Part 2

ciwaro as the plant icon of the American Southwest. It's got this large, round, vertical stem, kind of like a tree trunk, and then these limbs that branch out from the core when the cactus is mature. We were talking in the last episode about how the sowarro is probably just what a lot of people think of when they think cactus, despite the fact that its geographic range is somewhat limited compared to more widely distributed species like the

prickly pair. But it's just a fundamentally very charismatic plant. And the last time we talked about some reasons why that might be. It's sort of human shaped, you know, it's got a trunk kind of like a human maybe with arms looking raised in a posture that's kind of friendly. So in the last episode we talked about that. We also just generally introduced and described the species. We talked about the origin of its scientific name and the tie

into Andrew Carnegie. We got a bit into its evolution and some interesting features like its rib structure and its spines. And so we're back today to talk some more about the sorrow and should we do a pronunciation note people pronounce this word different ways. We have landed on sowarrow, but there are other options.

scholars named David Yetman, Alberto Burquz, Kevin Holteen, and Michael Sanderson.

form in them. You can see you know, you see those ribs, and you start thinking of them as a as a living thing, and so they they still cast their spell over you even as you sort of get used to them being there.

And we've already referenced their particular temperature requirements as well, like they have a part of their whole range issue is they can sustain certain amounts of freezing temperatures, but only a certain amount. And it's kind of like, you know, a few different factors what they can physically handle themselves, and then also the sort of power ups they get from their environment.

They open at night, generally after ten pm. And remember we're mostly talking about Arizona here, just a slim range in California. Arizona doesn't observe daylight saving time, so that ten pm is going to be pretty consistent as far as clock time goes.

pollination is key to the evolution of their flowers. However, while the flowers open at night, they're still visited during the day by daytime pollinators like various bees, and this includes indigenous bees and bees that have been introduced, migratory white winged doves and the doves and bees in general.

These two daytime pollinator sources are actually the most successful pollinators among the most northern northern of the Souaros, and according to the authors of that University of Arizona book that we reference, the reason for this is that most of the far northern Saros grow beyond the range of pollinating bats, and they're only able to survive it all

up there, most likely due to the bees. So they've kind of pushed beyond the range of the pollinators they evolve to depend upon, or at least that's the way it's shaken out over time. But the bees are keeping them going.

various ant and rodent species depend on the seeds. I don't know if we'll get into it in this episode or it'll be a subsequent episode, but humans, of course make use of the fruit. We'll come back to that. Termites will invade the plant to consume some of the soft tissues, but apparently never healthy plant tissue. There's a nineteen seventy seven study that the authors referred to here by Steinberg and Low, and in it it was revealed that the average sorrow produces some forty million seeds in

a lifetime. Few of these seeds. Very few of these seeds will survive long enough to germinate, and of those that do germinate, as few as one individual plant per parent plant will survive the first year, which is pretty pretty incredible. This despite a ninety percent germination rate given ideal conditions. There's just that much out there looking to eat the seeds, the fruit, or the sprout itself before it gets past that one year point and one year old,

soorrows are still tiny. I encourage folks to look up pictures of these. They If you've ever been to certain beaches, you may have encounted sand spurs, these little little little prickly bets with tiny spines on them. That's about what a baby, a one year old sorrow looks like.

So you might see the seed fall leave, come back ten years later and it's still you know, it's a little little guy like that. Growth rates do accelerate after that that early earliest decade, so it's not eight years for every inch or inch and a half of the cactus's height, but it still grows very slowly across its lifespan. The Jetman at All book says that after twenty five years, they are usually still less than a meter in height,

so incredibly slow growth. Depending on regional variations in climate, it usually takes somewhere between fifty and one hundred years for a swaro to get its first branch, the first arm coming out wave and saying hello. Between fifty and one hundred years for that, and a major factor in the rate of growth seems to be the level of moisture in the environment, so wetter conditions mean faster growth

and earlier branching, or at least usually mean that. The authors of the book also note that variation in temperatures during the winter to spring period seem to have a pretty powerful effect on growth rates, with temperature volatility in the early warm season negatively affecting growth, and I think this is a fact they link to the idea of

increased temperature volatility coming with climate change. Obviously that puts sorrows somewhat at risk, but even in the most favorable conditions, it's probably going to be fifty years before a cactus

goes from seedling to getting an arm. The normal natural full lifespan of the swarow is somewhere between one hundred and fifty and two hundred years, so you know they live, They live across multiple human generations and take multiple human generations even to become the more recognizable mature shape.

from freezes during winter. And this is interesting because whereas something like lightning strikes or wind might have a more you know, varied you might pick out individuals in a population, especially big top heavy ones, or you know, the individual lightning strikes might take out individual soorrows in a In the more northern regions, a local freeze can kind of wipe out a whole crop, a whole local crop of

cactus all at once. Another interesting fact they were talking about is that if you see a sar with a branch that droops downward instead of reaching up, you know it's got the arm turned down. This is often a result of injury from freezing conditions in the past. So maybe there was a freeze that didn't fully kill the cactus, but it injured the tissues, and so now it's got a drooping arm.

is right. Quote John Alcock, who monitored the same soarrows through the year over many years time, found that a mechanical injury as simple as constant rubbing by a palo verdi or ironwood branch could render a soarrow susceptible to disease and ultimate rot. So they are susceptible to especially if they get abrasions on their skin. You know, something kind of cuts into them, or hurts them, or just kind of rubs them enough, they can get these bacterial

or fungal infections. They can get these infections that ultimately, you know, spread through the tissue of the plant and kill it. The authors also provide some interesting and I think vivid descriptions of the death of a sorrow. To paraphrase Hemingway, the soorrow often tends to die slowly and

then all at once. So the slowly part is that you can get this kind of in between life and death zombie mode cactus stage where a doomed soorrow has been has been lethally injured, like it has been through a lethal freeze, but it may continue after that to stand upright and produce flowers, that produce flowers and fruit for years, but it's not going to survive. It is now doomed inevitably to die within a certain timeframe, usually less than a decade. But in the time between it

keeps on living, keeps on doing reproductive activity. But in the final stage of death this comes on with shocking speed. Quote, what recently appeared to be a healthy plant may over a period of a few weeks, turn yellow, then brown, then brown, with black streaks, branches will collapse and fall, and finally these sickly outer layers will slough off. And I connected this with images of the cacti that we talked about last time, with that peeled away skin. Look.

Another thing that the author has mentioned. I didn't make a note of this, but I just remembered it is you can get a weird situation where sometimes a big mature cactus gets knocked over, maybe it gets blown over by wind or something, so it falls over, but it's still sort of alive for a bit, so it falls but continues to produce fruit and flowers.

Yetna at All book. You mentioned earlier that the swaro tends to set fruit in the early summer, and this is usually going to be between June, mid June and early July, and that this is timed to come right before the summer monsoon rains. This is because the seed, you know, the goal is there's a seed inside the fruit, and the plant wants to disperse those seeds. And the seeds are going to be dispersed either by animal transport, so they'll be dispersed in the maybe the feces of

an animal that ate the fruit. This could be a bat or one of many species of bird, or sometimes it'll disperse just by falling. You know, it's not going to get as far that way. But yeah, it's trying to disperse the seeds. But when the seed hits the ground, the seed needs warm, moist soil in order to germinate. And the authors we're talking here about how a huge amount of the seeds fall in places where they're just not going to have a chance to germinate and survive.

Sometimes they get eaten by granivores like doves and bats, and then they'll get pooped out on a rock surface or inside a cave roost or some of their dark place, or they'll get dropped in an open area that's blasted dry by the sun, so they just don't have a chance.

dry in so many respects. You're in the desert. You're very concerned about how much water you have on you And at the time I was running just a little bit low, not dangerously low, but it was a little low. It's like, okay, I need to get back and get some water. But then you're also passing puddles that are

still standing. You know, you're you're you're stepping, you're walking through soft earth because of the recent rain, and so yeah, it can almost seem it can be very difficult to imagine, I think if you haven't encountered this in this environment.

that's not favorable for germination. Not to mention how rarely in time the overall climatic conditions align for the seedlings to germinate. The authors of the book note that quote the necessary conditions for germination of seeds and survival of seedlings seldom occur, perhaps ten times per century, often less frequently still, so that's sort of the good case scenario

tend to. You know, it can go be a long time in between the years when things work out just right for the young souarros to you know, to germinate and then to survive through their youngest lives. And this leads to two very interesting consequences. One is areas with tons of Sorrows all roughly the same size, and that's

because they're all pretty much the same age. It's like a cohort or a crop that came from one of these periods when they all grew up together, when the conditions were right, and so you're not getting a lot of in between because you know, there are long gaps in between these periods when conditions are right. And it also leads to areas that are Soorrow habitats, but at certain times in history seem to have no mature soarrows, and this latter condition can can cause and historically has

caused periods of what we might call illusory extinction. So the authors mention this in the case of the eastern unit of Soorrow National Park, where between the time the park was established in nineteen thirty six, and some surveys that were done in the nineteen sixties, nearly all of the mature souarros disappeared. Quote, what was once a soorrow forest became a comparatively uninteresting and structurally nondescript desert landscape. Now that's alarming.

the timescale of decades. Then you pair that with the extremely slow growth of the seedlings, and you can get periods where nearly all of the mature saros in the region reach the end of their natural lifespan, they die, and the younger generation of souarros are still tiny. So it looks like the cactus has just disappeared from the landscape,

but it hasn't. And in fact, in the case I just talked about the historical case with the eastern part of Suarro National Park, there was an additional human factor involved.

Researchers figured out why this illusory extinction occurred between the thirties and the sixties, and it was the combination of the generational dying of a crop of mature souarros plus several decades of climate being not very favorable to seedlings, plus human behavior in the area, primarily livestock grazing, which meant you know you're going to have cattle or whatever live stock just tramping through the area, so that you know that is negatively affecting the seedlings, but also people

cutting down woody trees for firewood or to fire kilns. And when these human activities were eliminated, the Suaros bounced back in the area and the cactus forest grew again. Now here's an interesting question. Why would people cutting down woody trees for firewood have an effect on soarrow seedling growth. This is another really interesting part of the young Souarro's survival gauntlet. So warrow seedlings need protection, and for this protection they rely often on what are known as nurse

plants or nurse trees. So rob I wonder if this matches with your experience of looking for the little seedlings

out in the desert. If you go out into the desert and find tiny soorrow seedlings thriving, especially in the colder parts of the Sawaro Range, the more northern parts, it's usually the case that these seedlings are hiding under the protective cover of a larger established plant, with the most common species including the pallaverdi, the ironwood, creosote, mesquite, and another shrub called the triangle leaf bersage or barsage. I don't know how you say that, did you observe

this kind of thing? I've got a picture, by the way, you can look at in the outline, rob where you've got these young sowarrows, all kind of they're almost gathered like children around a mesquite tree. You know, they're under its branches and they're springing up around it.

the case. It's a it's a very very botanically diverse area. There's so many different types of cacti as well as as other plants that have evolved to thrive in dry conditions, and so you see this multi layered effect going on, things living and thriving in the shadow of other plants, you know, pretty much throughout these landscapes.

for you. The flesh of the soorrow is actually tough, acidic, contains irritants. It's just like not very palatable. There are some creatures that can kind of consume it. But unlike that, the tender cudaledans of a freshly germinated seed are relatively easy pickings for rabbits, mice, and pack rats, ants, birds,

all kinds of things want to eat the seedlings. The seedlings are also easily crushed underfoot by larger animals like deer or grazing cattle you know, livestock animals, and they are vulnerable to the sun, so if they don't have

adequate shade, they will get roasted and desiccated. On the other hand, if they don't have protection against the cold, they will easily freeze to death because they don't have the mass that the adult cactuses have that helps protect them against freezing as they don't have the mass or the defense mechanisms of mature souarows that allow them to

survive these short dips below freezing temperatures. So the authors of the book right quote, nurse plants are so named because their shade branches litter, plus the other plants that grow in their shade shelter the seedlings from sunburn and freezing, protect them against trampling, conceal and shelter them from herbivores, and, in the case of some luguminous trees, provide a nitrogen enriched soil environment. So the nurse plant offers the whole package.

It keeps you from burning. Not burning keeps you from dry you know, getting too hot, drying out and desiccating keeps you from freezing, keeps animals from eating you or crushing you. And sometimes it even gives you some natural fertilizer.

So it's a nice deal, right. It would almost be nice if the soaros could find a way to pay back their nurse plant somehow, But in this case, what goes around does not come around, because it seems what often happens is by the time the sowarrow is becoming large enough that it has its own defenses and it has enough mass to survive frosty weather and doesn't need the nurse plant's protection quite so much anymore. It also,

at this point has a pretty robust root structure. Now we haven't talked a lot about the root structure of the toworro, but it tends to unlike other plants which have a deeper taproot goes down deeper in the soil, the soworrow tends to have a wide, shallow root structure.

And what this does is it kind of sucks up a lot of the rain water that would previously have seeped down into the soil and been absorbed by the deeper roots of the nurse tree, and in this way, the growing soworrow may quite often sort of murder the plant that raised it, or if that's putting it too strong, it at least starts to outcompete the plant that raised it.

Very is this the thanks I get situation? However, because the growth of the sorrow is so slow, the author's point out that this process never serves to wipe out the population of nurse plants in an area because the nurse plants have plenty of time to reproduce and recruit new generations before they are sort of betrayed and destroyed.

plant canopies. I think it could be that there's, you know, just other factors come into play, like they're more in competition for light and stuff like that. But whatever the reason, they don't do as well under plant canopies in the southern part of their range, so instead they are found more isolated from other plants in rocky areas, where they rely on rocks and boulders to provide the kind of shelter that something like palloverdi and other plants provide further north.

A lot of the plants gathered there, and they also kind of help shade and protect each other.

It's like this plant is growing next to this one, in the shade of this one, in the partial shade of this one, in the soil that is manipulated by this one. You have an entire ecosystem going on there, and it's it's more than it's more than just the individual. And I guess part of that too is like humans have an individual spirit, and we are also often prone to think about ourselves as being disconnected from everyone else around us in the world and the people that came before us.

its flesh. And some of the authors we talked about in the last episode compared the cactus to just an enormous drum of water, like a giant standing drum of what I mean, that's quite true, Like much of its mass is water.

And you know, the spines do help with that, but they also help with water and they help with controlling the microclimate around the cactus because the spines help shade the surface of the cactus under the hot sun, mitigating evaporation. And they also i'll trap a boundary layer of warm, humid air around the souarro's skin, kind of like wearing a sweater.

the Nightstalker. But the connection to Spanish moss is that it also makes use of cresulation acid metabolism for roughly the same reason as the cactus, which is to preserve moisture. So what is CAM photosynthesis? Like other plants, the sowarro gets its energy through photosynthesis, So, in simplified terms, it uses sunlight to power a series of chemical reactions which take carbon dioxide that it absorbs from the air through these little holes. Most plants have these little holes on

the undersides of their leaves. In the case of the cactus, it's going to be these little holes in the stem which can open and close. These are called stomata, and they open and close to absorb carbon dioxide from the air, and then they fix that carbon dioxide into sugars into carbohydrates. And so for this reaction, the plant actually does need water, which it absorbs through its roots, and the chemical reactions produce the necessary carbohydrates for the plant to live, sustain itself,

and grow and reproduce. These are the energy storing molecules. And then the reactions also produce oxygen as a byproduct, which is very lucky for us, lucky for all of the oxygen breathing metazoins out there. But the most common form of photosynthesis in the plant kingdom is known as C three carbon fixation. Something like ninety percent of plants use C three. There's another type known as C four carbon fixation. Crasulation. Acid metabolism is an alternate form of

photosynthesis that it still does basically the same thing. You know, the beginning and end is roughly the same, but it uses a few extra steps. The CAM pathway comes with a reduced total carbon carbon output, so it's gonna be less productive overall for the plant. But what this pathway sacrifices in total energy molecule production, it makes up for in water preservation because it saves water. Most species of cacti, which are adapted to hot and dry conditions use CAM photosynthesis.

So what's the trick here. I'm not going to go into a full depth on the chemistry, but the major macro scale distinction of camp photosynthesis is that it allows the plant to keep its stomata closed during the daytime. And remember that the stomata are these little tiny holes or pores in the skin of the plant. Again most often on the underside of leaves, but in the cactus they're going to be on the outer the layer of the stammer of the arms, and these little holes allow

the exchange of gas and vapor with the air outside. Now, a C three pathway plant will keep these pores open during the daytime so that the plant can continuously absorb carbon dioxide from the air while the sun is shining to power the photosynthesis in its leaves, so in the C three pathway, it's like the raw materials are being delivered to the factory while the assembly line is running.

But for the suaro in the desert environment, having the stomata open during the day is a dicey proposition because the sun is blazing hot, the air is very dry, and those conditions together mean that a lot of water inside the plant will be evaporating and escaping while the

windows are open. So instead, what the soarro does is it keeps its pores closed tight during the daytime and then opens them instead at night, when there will be less evaporation and water losc as temperatures are lower, so it feasts on CO two after midnight by the light of the moon. Now, like any other plant, it still needs sunlight to power photosynthesis. It can't do anything about that. It needs to use the sun to power the reactions,

and there's none of that at night. So cam photosynthetic plants have to convert the absorbed carbon dioxide from the night time into an organic compound called malic acid, where they can store it for later use. Now it's important to note that malic acid is not an especially weird or exotic compound. In fact, it is produced by I think every plant on Earth, or if not every plant, nearly every plant. Most plants at least maybe all of them make this stuff. And you are already quite familiar

with malic acid. I can guarantee by taste because it is the main chemical responsible for the tart flavor, and a ton of fruits like unripe apples, grapes, pears, and plums, apricots, all these fruits are going to have a sourness that comes from malic acid. Now, of course, it's not the only source of sourness in fruits. You also have citric acid, which you get in citric fruits and stuff. But malic acid is going to be the tartness in a lot

of natural fruits and some vegetables too. I think it may be a dominant flavor in rhubarb, I think I've read. And one in Tristing fact I came across is that it is sometimes even used as the vinegar flavor in salt and vinegar potato chips. Are you a salt and vinegar guy, Rob.

called the Science behind Salt and Vinegar Chips. This guy went through and studied the ingredients of a bunch of different brands of salt and vinegar potato chips, and he writes, quote, surprisingly, a couple of brands in our lineup opt for citric acid from citrus fruits, malic acid from apples, lactic acid from milk, or even fumeric acid which apparently comes from lichen and the quote continues to give them pucker and punch. So I was looking through which ones are the ones

that opt for malic acid. Some very familiar brands like lays, Uts and Whys all use malic acid in their flavoring mix. So it's not the only flavor there, but it's part of the flavoring they use for the chip. And while well, not all tartness is exactly the same, you know you'll get different acidic types of flavors, and malic acid is going to have a slightly different kind of tartness and acidity than acetic acid from vinegar or citric acid. So yeah,

I don't know. I guess they just try different things and figure out what flavors they like. But sometimes you're going to be getting malic acid in your chips.

as malic acid. It's brought in during the night and then turned into malic acid stored there, and then once the sun fires up in the daytime, the plant can close its pores tight to protect its horde of water and minimize evaporation, and then vert the malic acid back into CO two inside its tissues and then fire up the photosynthetic assembly line. So rough analogy, it's kind of

like having a form of cold storage. It's a place you can store the materials you need when it's not convenient to be getting them at the same time you're using them.

the tequila element. Of course margarita, you're gonna have what's the other stuff in there? I think orange, liqueur or something and citrus. Yeah, but the tequila part itself, Some of these flavors are downstream products of crasulation acid metabolism. Another cam plant is vanilla. Now this one is not

fully cam. I'll discuss the distinction in a minute, but this is interesting because the orchid flower that produces vanilla vanilla beans doesn't grow in especially dry conditions like the desert. It tends to grow in kind of, you know, moist forest conditions like the dense, shady understory of a humid tropical forest. So if the I was wondering, if its environment is pretty wet, why does it need cam the

answer to this question. I had a harder time finding a very clear CLI answer to this, and I was seeing suggestions of different reasons in different sources. So maybe it's kind of complicated, but it seems one possible part of the answer brings us back to Kulchak, the nightstalker and paramou Fa. So remember that Spanish moss is an epiphyte, meaning it grows not on the ground but on the

trunks and branches of trees. And because it grows on trees, it can't put roots into the ground to collect moisture, so it has to collect moisture from the air and directly from rainfall with these epiphytic roots or with these things I think called tricombes on its outer tissues. So this is a less stable, less dependable way to get water compared to having roots sunk in the ground. Thus it needs to use cam to protect what water it's able to suck out of the fog and out of

the storm. Vanilla orchids are not full epiphytes, but it seems they are semi epiphytes, so they do they have roots in the ground, but they climb up trees. They climb up the trunks and branches of trees like vines, and as they climb up they produce these secondary aerial roots to absorb water directly from the air and from

the rain. So kind of like Spanish moss, the aerial roots are a less stable, less consistent way to harvest water than the roots sunk in the earth, and so this could be a reason why these vanilla flowers rely on CAM at least in part. Could be other reasons too. It might have to do with light and heat stress in their hot environments, maybe as they like climb up trees and become exposed to the sun. But whatever the reason, when you taste vanilla, you can think about how wow,

you know? So the compounds that I'm tasting now are downstream of growth through in part crysulation, acid metabolism. And it's worth noting that the different photosynthesis pathways are not mutually exclusive for a plant, so many plants can switch between like direct C three photosynthesis and CAM depending on conditions. It seems like vanilla orchids do this. A lot of camplants use C three when water is abundant, and then they switch defensively to the CAM pathway when they are

under thread of drought. This is called facultative CAM photosynthesis. But the swaro is an interesting exception. It is one of the rare plants that, as far as we can tell, basically never goes into C three mode. It is pretty much only CAM, which is called obligate camphotosynthesis and coming back to the Jetman at All book, there's this whole interesting section about this in a chapter by one of the authors, Kevin Halteen. Halteen writes about some experiments that

demonstrate and study the suarro's obligate relationship to CAM. One way you can do this is you put the soworro inside an air type plexiglass box and then measure the amount of CO two in the air in the box over time. And sure enough, these experiments show that carbon uptake by the sowarro is almost entirely confined to the nighttime it's after midnight. In a period between midnight and dawn and the rest of the day, carbon uptake is

either zero or it's actually negative. So during the day it's you know, releasing carbon dioxide, which we don't usually think of plants doing. So why would that be going on?

I guess there could be multiple reasons, but Holteine explains that this is actually pretty common for cam plants during the day because it happens when the malic acid is inside the tissues is converted back into carbon dioxide, so the photosynthesis can happen some of this co two escapes from you know, it leaks out of the plant before

it can be converted into sugars. And another interesting thing that they note is that the suaro shows differential carbon uptake across the seasons of the year, regardless of some objective external conditions like the amount of water present. This seems to be an adaptation related to the fact that they grow more in the summer and then they shift into a more conservative, safer gas exchange strategy in the off season when less new tissue growth is needed.

It's what everything revolves around.

certainly feel free to go ahead and ride in. Any of you desert dwellers or desert tourists out there, or cartoon watchers and Western officionados. We'd love to hear from you as well, if you have thoughts on anything we've discussed about the souaros thus far, or any media representations and so forth. It's all fair game. Just a reminder to everyone out there that Stuff to Blow your Mind is primarily a science and culture podcast, with core episodes

on Tuesdays and Thursdays. Short form episode on Wednesdays and on Fridays, we set aside most serious concerns to just talk about a weird film on Weird House Cinema. Yes, I'm not sure if we have watched a film with the sowaro in it. We have watched some, We've watched desert movies. We've watched Arizona movies, but I don't know if we've watched anything filmed specifically in the Sonoran Desert. I'd have to go back and check, but I'm not sure.