Indoor Plants as Air Purifiers

This is weird to write, but it's been bugging me for a while now, so I figure I have to. I see a lot of people asking – more on line than in-person at work, but there's some of both – about which plants are good at removing chemicals from the air, and where one might find these plants. Semi-recently, I had a customer who was very insistent that she had to have some plants from this specific list (out of Reader's Digest: she'd brought the magazine in with her) because those plants had been tested by NASA, and they were good toxin-removers, and anything else might be nice and all, but unless NASA had proven it would improve air quality, she wasn't interested. Another subset of customers want some plants because of their capacity to produce oxygen, and have been told by the deluded or unscrupulous that more oxygen is the Answer! at long last! if you're feeling tired or run down.

Pictures in this post are of various NOID mums from work,
and are only tangentially related to the topic at hand.
This is what we call junk science. Junk science is stuff that's true in some fashion or another, but horribly misunderstood, distorted, or incomplete. This is distinct from pseudoscience, which is stuff that isn't even a little bit true, but is dressed up in the language of science (vibrations, energy, metabolism, crystal lattices, toxins, quantum, etc.). Plants are tools of both, though not very often – generally the peddlers of junk and pseudoscience want you to buy something manufactured, not a plant, because manufactured things won't propagate themselves. If there's a plant involved, it's usually been ground to a fine powder, or reduced to a picture somewhere in the logo.

Part I: Oxygenation

Let's start with the oxygen claim, 'cause it's easier to take down. First of all, in order for this to work, we have to assume that your home is airtight. If you're going to be opening your doors and windows, then all bets are off, because any (allegedly) beneficial accumulation of oxygen is negated once all the air inside your home has been replaced with air from elsewhere, an event which is called an "air exchange."

This first qualifier excludes everybody who's reading this. The average home completes an air exchange about once an hour, and the EPA recommends sealing your home tighter, to extend this to about every 2 hours and 51 minutes. I'm not saying that the air in your home is identical in every respect to the air outside: things can build up. However, there's always a point where the oxygen you generate inside is balanced out by the amount leaving, whatever those relative amounts might be. At that point, there's nothing you can do to increase the average oxygen level in your home except to produce it faster (as by getting more plants) or get it to leave slower (as by sealing your home up even tighter). If all the air is turned completely over every hour, or even every 2 hours and 51 minutes, then that's not going to allow for a whole bunch of buildup of anything. Keep this in mind for later.

When photosynthesis happens, oxygen is produced. In order for the oxygen to leave the plant, though, carbon dioxide has to come in, one for one, and a molecule of carbon dioxide (CO₂) weighs more than an oxygen molecule (O₂). This means that the plant is going to put on mass over time, but we already knew that that happens: we call it growing. I'll spare you the chemistry, but when all is said and done, the plant adds one molecule of glucose for every six oxygen molecules it gives off.


So we can use this fact to do some math. I'll stick the math in a footnote, so as not to rile the mathphobic in the audience, but the upshot is, just to increase the oxygen content in a small bathroom, say 6 feet wide by 8 feet long by 8 feet tall, by a small (probably not even noticeable) amount, say 1%, over the course of a day (let's assume that the air exchange rate is once per day, which is more than eight times more airtight than the EPA recommends and is therefore damned unlikely) you'd have to have a plant in there that was putting on dry weight at the rate of 11.1 kg/yr (or 24.6 lb/yr).¹ And this is to change the composition of air inside of a very tiny room by a very tiny amount. So, ma'am? That peace lily you're buying isn't even going to oxygenate your bathroom, much less your whole ground floor.

But – and this is really my main point here – that's okay. You wouldn't necessarily want it to, even if it could. Unless you are right this minute drowning at the bottom of a swimming pool, in outer space, suffering from carbon monoxide poisoning, adjusting to a move to a higher altitude, or in need of supplemental oxygen due to emphysema or some other lung impairment, you're already getting all the oxygen you need. Even if you feel tired and run down. You're probably not sleeping enough. You may not be eating well. You could be depressed. But lack of oxygen is not your problem. If everybody feels tired and run-down because of lack of oxygen, and oxygen only comes from plants in one's immediate vicinity, then: please explain this to the Inuit, who live a plantless existence on ice and permafrost for most of the year. (But explain it to them quickly! They have no oxygen!)

And furthermore (since this dead horse is just laying here, I may as well beat it), if you think about it, the odds are pretty good that just outside your door, or maybe the next county over, there is a very large biomass of plant life just photosynthesizing like mad, in the form of a lawn, or a farm, or a tree, or whatever, which probably puts on all kinds of biomass in a year. Unless you went to completely ridiculous extremes to fill your home floor to ceiling with houseplants (and I don't know what kind of insane person would do that²), any contribution from your houseplants is going to be completely swamped by the plants outside every time you open the front door.

And if that's not enough, most of the oxygen on earth doesn't come from land plants in the first place. Wikiposedly (I couldn't confirm this with anything more reliable, though it makes sense), 70% of the oxygen in the air comes from sea life, algae and cyanobacteria and such. Your spider plant, however big and lush, is just not that big of a deal.

Part II: Toxin Removal

The word "toxin" used to have a more specific meaning. I'm not sure who to blame for the change, but now instead of meaning "something that can and will cause you harm if it gets in your body," it seems to mean "tainted" or "contaminated:" it's more of a psychological word than a physical one. There are a lot of products out there which purport to cleanse toxins out of your body, but there's not a lot of detail on the questions you'd think would be important, like: Which toxins? How did they get there? What happens if I don't remove them? How do you know? A skilled charlatan will have a blizzard of junk science to throw at you; a less-skillful one will have to use pseudoscience and hope you don't know the difference; the newbies will change the subject.

That said, there really are, probably, some things in your air right now that aren't good for you. Exactly how bad we're talking depends on what it is, and where it's coming from, and how frequent your home or office's air exchanges happen, but sure. Not everything in your environment is as pure as the driven snow, the driven snow included.


That said, it's not likely that these chemicals are going to be what finally does you in. They may not even contribute to it, not even a little bit, or reduce your quality of life in any way. But they're also not going to make you healthier, so you may as well get rid of what you can, and if doing this involves a plant, well, plants are pretty, or at least can be, and having pretty stuff around improves your quality of life anyway. So go right ahead: I've got no problem with that. But keep in mind when you hear and read these things that the whole plants-will-save-us-all crap may have been just a weensy bit oversold.

Where this whole plants & toxins thing crosses a line, for me, is the point when people think that it is very, very important that they get a plant for this one, specific purpose. They don't care what the plant looks like, they don't care if they have the conditions to support it, they don't care about the price: if it's on the list, then they have to have it, and it's an emergency.

There are situations where it might actually be sort of an emergency to do something about chemical vapors in your home. For example, if you survived Hurricane Katrina and got moved to FEMA trailers provided by the government, who knew that the trailers' air contained levels of formaldehyde 75 times the maximum level considered safe for workplaces but stuck you there anyway. (Remember when I asked you to keep in mind how oxygen never gets much of a chance to build up in the air, because the air cycles through so fast? Imagine how much formaldehyde has to be being released, continuously, to build up to levels 75 times the amount considered safe. Imagine how much higher the concentration would have to be at the source of the formaldehyde, then, like kids playing on the floor next to off-gassing carpet, or sleeping with the head of your bed pushed up against an off-gassing wall.) Then, it might be kind of an emergency to get some plants. Though in that case, you probably don't have enough room or money for the number of plants it would take anyway, so the whole discussion is still kinda moot.³


Although different plants do seem to preferentially take up one chemical or another, I've had trouble finding anything reliable-looking on-line about any chemicals except three: trichloroethylene, formaldehyde, and benzene. So, in the unlikely event that you're sure you have an issue with one of these, do the research and find a plant that will get rid of it. Most of us, though, aren't going to know which chemical might be our main problem. Since 1) it's hard to find specific chemical/plant match-ups anyway, and 2) all plants have some capacity to absorb organic compounds from the air, I say buy what you like and don't worry about it. In general, plants with more surface area will absorb unwanted molecules from the air faster and more completely than plants with less. So you're better off choosing bigger plants rather than smaller plants, rainforest plants rather than succulents, fast-growing plants rather than slow-growing plants. But this isn't a life-or-death thing, and anyway, you're (in theory) going to be living with this plant for a while, so you may as well get something you enjoy looking at.

This is true even if it's not something that NASA specifically checked out.⁴ On the other hand, many of the NASA study plants are quite nice, including several that have already been the subject of plant profiles here at PATSP, so there's also no reason to exclude something from consideration just because it's on the list:

Aglaonema spp.
Chamaedorea seifrizii
Chlorophytum comosum
Chrysanthemum morifolium
Dracaena deremensis 'Janet Craig'
Dracaena fragrans 'Massangeana'
Dracaena marginata
Epipremnum aureum
Ficus benjamina
Gerbera jamesonii
Hedera helix
Philodendron hederaceum (a. k. a. P. scandens, P. oxycardium)
Philodendron selloum (a. k. a. P. bipinnatifidum)
Sansevieria trifasciata
Spathiphyllum spp.

The NASA recommendation was for one eight- to ten-inch plant per 100 square feet of floor space (some sources say six- to eight-inch; I'm not sure which was the actual original suggestion); based on my best guesses of how that scales up and down to four-inch plants and sixteen-inch plants and so forth, I think I have at least nineteen times more than the recommendation. We have really, really non-toxic air here. Or so goes the theory.

One note of caution: in some situations, having a plant inside can actually make air quality worse, at least in a sense: certain plants are known to cause allergic reactions in some people, and if dried sap, for example, is on the surface of a leaf and then gets stirred up by the wind, or a featherduster, or whatever, then it could, in theory, lead to some respiratory distress, though I was unable to find evidence that this had ever actually happened to anybody in any kind of life-threatening way. I assume that the same plants that are known to cause contact allergies would also be the worst offenders on this count, so Ficus spp., Euphorbia spp., Synadenium grantii, Hedera helix, Pedilanthus tithymaloides, Yucca guatemalensis, Agave spp., and so on, might not be the plants you want for this, if you're extraordinarily sensitive to plant materials in general. Or use pots filled with dirt, which also works, though not as well.⁵

I'd prefer that the people buying houseplants were buying them because they liked them, not because they're expecting them to do a job. And I'd really rather that the people buying them weren't expecting them to give them super-oxygenated energy! or remove toxins (for "toxins" read evil itself) from their environment, because this is a lot more to ask of a plant than most plants are capable of, and all involved are likely to wind up disappointed in the end.

[shrug] It's not up to me why people buy, obviously. I suppose I just don't relate to people who need an excuse.

-

¹ Air is 78.08 % nitrogen, 20.95% oxygen, 0.93% argon, and the rest is miscellaneous junk (carbon dioxide, helium, neon, methane, ammonia, water vapor, ozone, nitrogen oxides of varying configuration, carbon monoxide, radon, krypton, sulfur di- and trioxide, hydrogen, etc.).

1 kilogram = 2.2046 lb.
The volume of one mol of any gas at standard temperature and pressure is 22.4 L.
The molecular weight of oxygen is 32.0.
The molecular weight of glucose is 180.16.
-
6x8x8 = 384 ft³. So then,

(384 ft³) x (28.3168 L / ft³) x (0.2095 L O₂ / 1 L air) x (1 mol O₂ / 22.4 L) x (32 g O₂ / mol O₂) x 1% = 32.5 g O₂. This is the mass of one percent of the oxygen in the room in question.

(32.5 g O₂) x (1 mol O₂ / 32.0 g O₂) x (1 mol glucose / 6 mol O₂) x (180.16 g glucose / mol glucose) = 30.5 g glucose / day.

(30.5 g glucose / day) x (365.25 days / yr) x (1 kg / 1000 g) = 11.1 kg glucose / yr.
(11.1 kg glucose / yr) x (2.2046 lb / kg) = 24.6 lb glucose / yr.

This is a lowball estimate, because of course plants do things besides making glucose, like for example making proteins (for which they need nitrogen) and DNA (which involves phosphorus). Uptake of nitrogen and phosphorus, as well as the various other elements plants are made of, will increase the amount of mass involved still more.
² my "office:"

³ So, you may be wondering how the formaldehyde got in there in the first place, and why it stays. Well. For reasons too complex to go into here, a lot of foams, glues and plastics are produced by reacting formaldehyde with some other substance (in fact, Bakelite, the very first plastic, was produced by reacting formaldehyde and phenol). There's always a little of the reactants left over, and they can only be washed off the surface. Other products that aren't actually made with formaldehyde can break down into formaldehyde (and other things) over time. A third group of things is deliberately permeated with formaldehyde to kill mold and bugs and such, a fraction of which stays in the product. So all three kinds of materials are going to be continually leaking a little bit of formaldehyde from the center of whatever it is, until it's all evaporated away, a process which is usually known as "off-gassing" in the environmental literature. Wikipedia has a list of stuff that (wikiposedly) releases formaldehyde, though this won't probably mean much to you unless you're fairly versed in chemistry.
There is the occasional product where release of formaldehyde is the whole point, as for example imidazolidinyl urea, an antimicrobial added to certain shampoos and other cosmetic-type products. Imidazolidinyl urea can protect a product against mold and other unwanted organisms because it is constantly releasing a small amount of formaldehyde, which is sufficient to kill anything off before it can get itself established; consequently, you can squeeze the shampoo out of the bottle in the shower without having to worry about it having embedded chunks of mold, which I think most of us would agree is a good thing. (I know Martha Stewart would agree that it's a good thing. Unless she makes her own shampoo. I bet she makes her own. So never mind.) Though I doubt the Katrina survivors' trailers have high formaldehyde levels in them because they're full of shampoo.
Indoor air normally contains about 10-20 parts per billion (ppb) of formaldehyde. The work-safe level is currently set at 8 ppb by the CDC. The average level in the Katrina trailers was 77 ppb, though there was quite a range: at least one test showed a level of 590 ppb, which is a whole hell of a lot.
⁴ The original NASA-approved list seems to have been expanded somewhat since the original studies were published, or at least you'll find longer lists than mine at some other websites. Whether this is because people spontaneously expanded the list to include their own favorite plants, or because of common-name confusion and people copying one another's lists, or because there were actually additional studies done more recently, I'm not sure. It doesn't change my basic point, however big or small the official NASA list is.
⁵ No, seriously. One of the NASA tests on Chlorophytum comosum and another plant I can't remember (Epipremnum aureum?) used a Plexiglas box containing a certain concentration of formaldehyde. In order to see how much of the formaldehyde being absorbed was the plant, instead of the soil, the pot, etc., they ran a control test with soil-filled pots of the same size. The soil removed a third of the formaldehyde on its own, taking the concentration in the box from 15 ppb to 10 ppb. It's easy to forget about the microbes in dirt, even sterilized dirt, but they're still there.

Random plant event: Polypodium formosanum 'Cristatum'

This isn't really so much a random plant event as just a random plant, but whatever. In the post about the shoplifter, I mentioned that there was a weird plant in the latest shipment that was going to get its own post soon: this is that plant.

It's a little unusual from the top:


But the foliage isn't even the part we're interested in. It came in with a batch of "footed" ferns -- rabbit's-foot (Davallia) and bear's-paw (Polypodium?) and that sort of thing. So check out what we saw when we looked at the "feet:"


The picture doesn't quite do it justice, but it was the best I could do. The "feet" are smooth, and sort of a light green -- more than one co-worker spontaneously compared them to Manduca sexta, the tobacco hornworm, though hornworms are thicker. And more mobile.

The supplier helpfully provided tags with the scientific name and the suggested common name of "E.T. fern;" I don't know if I expect that to catch on, but it certainly got my attention. In any case, it looks like a footed fern mutant that doesn't grow "fur" on the "feet." I'd buy one, but we're kind of at the low end of the annual cycle with my rabbit's-foot, where it's just starting to come out of dormancy after spending all winter looking increasingly like crap. Taking on another fern seems like asking for trouble. But maybe eventually.

Unfinished business: Ludisia discolor blooms

Just before Christmas, I posted excitedly with the news that the Ludisia discolor ("jewel orchid") plants in the greenhouse were all budding, and I was excited about what the flowers would end up looking like. Then they all got sold before any of them opened up, so I never saw even one flower, which was depressing. Well. In last week's tropical order, we had some come in that were already in bloom, so now I know, and I took pictures, so you also can know.

The bud:



And then the flowers:



A little anticlimactic, no?

The shoplifter

So I'm in the back of the store, trying to put away the tropical order (which arrived on Wednesday: pictures of three of the more notable plants are scattered throughout this post, though the weirdest one is going to get its own post in the near future), when Younger Co-Worker comes back and tells me, You should go out there; there's a guy who I think is just standing by the Joseph's coat or whatever it's called, breaking pieces off.

He's what?

Just go go in there and see.

Tillandsia xerographica. This plant is something like 10 inches in diameter, and is impressive, but I strongly doubt that we're going to convince many people to pay $30 for one. ($30 is actually cheap: with our usual mark-up it should have been $40. Certain people had to be talked into reducing the price.)
So I go in the greenhouse and look around, and there's only one guy in immediate sight, who sees me see him and immediately asks me something I don't remember, about Begonias. I remember the phrasing was weird -- something along the lines of, I need to steal a couple leaves from one of your reddest Begonias. And we look around at Begonias for a bit, and he's chattering at me the entire time about how he's connected with the University of Iowa¹ and there's some guy there who's got this thing he does with dissolving cell walls away until the protoplasm from differing cells can be combined together, and he has to have really red leaves so they'll be able to tell whether or not it worked, etc., which chatter is actually moderately interesting.²

Anthurium andraeanum 'Florida,' at least according to the tag. The picture is more or less true to the actual color: it's sort of orange-but-not-orange. Yellow spadix. WCW and I were both unwilling to buy a whole plant (they were pricey), but we divided one between us and are buying most of the pieces of that instead. WCW, by the way, said that she'd had dreams already about some of the plants that came in in this last order, that she wants some of them that badly.
And I think to myself, I should really probably make sure he knows he's going to have to pay for those, and I consider saying just flat out, "You know you have to pay for those, right?" but I don't, because that's, you know, awfully blunt, and for all I know the University has some special arrangement with us to where they can take stuff like this from time to time, for their purposes, whatever those purposes may be. So I figure, okay, no, I'll just go up towards the front with him, and jump behind a register and tell him $3.25³ or whatever, and that actually would have worked, except that another customer caught me at that moment and asked me a question about a fern, and while I was answering her question he blew past me, through the store and into the parking lot.

So then I go to the boss as she's leaving for lunch, and while she's telling me that she's leaving, the guy pulls out of the parking lot right in front of the window where we're standing, and I get his license number and ask the boss for a pen, and then I ask her, So, um, do we have some kind of special arrangement with the University where they can come here and take cuttings and leaves and stuff for free? And she says no.⁴ And I'm like, oh. 'Cause the guy who just left, with this license number, just did that.

Euphorbia bougheyi variegata. I bought this particular specimen a couple days ago, because I remembered Aiyana said she had one a while back. Also it's pretty.

And then there was a rehashing of the part of the story I've already told you, followed by a minor lecture about watering the petunias, some of which have gotten too dry recently. So not a huge deal. Also he didn't really get much of value: he did get some rex begonia leaves, but most of them were the mildewed ones, which were also scorching from being in front of a heater and which we were unlikely ever to sell anyway. Plus we haven't been able to propagate the Alternanthera dentata lately from seeds⁵ or cuttings either one, so even if he got cuttings off of that, they're probably worthless to him. He may only have gotten a couple leaves from some cane-type begonias, and they'll be growing more soon enough. So no real damage done. We're unlikely to prosecute: it'd cost more to get what we're owed than to just ignore it. But I just hate getting played like that, particularly since I did kinda know better and did think about making the right call. Damn this midwestern niceness! It's a curse, I tell you.

-

¹ (plausible: half the town seems to be connected to the University of Iowa in some way or another)
² Though now that I think about it, he was probably bullshitting me. I remember he threw in some comment somewhere in there about how "and this doesn't count as genetic engineering," which -- the fuck it doesn't! That's totally genetic engineering! And there was something else where he was talking about dissolving the cell walls with cellulose, which a real scientist would have known was actually cellulase, and a few other things like that. He was talking very quickly, though, obviously, so I had to kind of ignore shit like that if I was to have any hope of following the conversation.
³ This is also the price of a 3-inch plant, and is kind of the default charge for people who want to buy cuttings.
⁴ (To her credit, she said it fairly nicely, not at all in the oh my god, I forgot you're retarded sort of tone that I would probably have used had our positions been reversed.)
⁵ (Well I think they're seeds: the flower heads have been dropping pieces of themselves when the plant gets bumped, so I'm assuming. Though we still haven't been able to sprout them yet.)

Movie

Nothing about this ad is true. We are not encouraged to throw the plants through the air. We don't have any hoses that are capable of delivering such precise bursts of water. Also our aim is not that good. Traffic flow is rarely, if ever, that smooth. Flowers don't grow that fast. Flowers don't wilt that fast. Paying by check card is not faster than paying by check (and cash, contrary to some of the other ads in this series, is considerably faster than either).

That last point, that cash is faster, and checks are at least not slower, bugs me every single time one of these ads comes on. Speaking as a cashier of some experience, what mostly slows down lines are the customers who are completely oblivious to the idea that they're going to have to pay until they hear a total. Have whatever you're paying with ready to go while the stuff is getting rung up. Start filling out the check, start swiping the credit card, start counting out the approximate amount of cash. Don't force the cashier to ask for a method of payment. It makes them crazy.

Mr. Brown Thumb not dead! Or even injured!

I figured this was worth making a separate post out of, for those regular readers who aren't on Blotanical, because if it's been bothering you half as much as it has been me, then this will be a relief.

According to Carolyn Gail at Sweet Home and Garden Chicago, friend of the blog Mr. Brown Thumb is in fact alive and well, albeit with a spectacularly lame excuse for not posting for the past two months (or, apparently, checking the messages on his blog, or his e-mails, or etc.).

Now if we could just get Tracy to come back.

Behold the power of Teh Internetz! / More bunnies?

Not too long ago, I posted some pictures of assorted plant discolorations and -figurations that were going on at work, and asked the internet in general for ideas about what was going on. Nothing clear emerged until very late in the game, where jean001, at Garden Web, said it looked like edema, which quickly became my favorite theory.

And then one of my co-workers talked to people from the plant diagnostic lab at Iowa State University (Ames, IA) and told me that they said it was probably mechanical damage, from being sprayed with pesticide right before shipping. Which was disappointing.

Well, I'm pleased to report that jean001 (and, to a lesser extent, I) has been vindicated: we received the official final report from Iowa State yesterday, and it reads, in part:

Microscopic examination revealed that the spots were caused by blistering of plant cells, not by damage from an insect or pathogen. We consulted with [redacted] and [redacted], both of whom said that the damage looked like edema, which is consistent with our microscopic observations. Edema occurs when plants take up more water than they can transpire through their leaves, and it can occur after humid, overcast weather, or occasionally in response to some chemicals.

So the official word from Iowa State is edema.

And this would be totally and completely awesome, if not for the fact that we have two new things going on now. One is, again, on a geranium, and my personal suspicion is, again, edema, though other theories have been proposed as well, some more far-fetched than others.



No insects, droppings, or webs were found on this leaf, nor do we have pest problems I'm aware of in the greenhouse except for fungus gnats and spider mites, and the spider mites are quite a ways away, as far as I've seen. Several of the geraniums in the general area of the one photographed are also doing this, but to a much lesser extent. General climate conditions recently: we've had a very springy spring so far, just like we had a pretty wintery winter. Occasional days with sun and highs in the 50s and 60s, but recently snow and upper 30s. It's been cold for the last couple days, which is a lot of why I suspect edema.

A second problem is on something completely different, which unfortunately I didn't bother to learn what plant we're talking about, but maybe it will suffice to say that the yellowing and bumpiness on the leaf in the center of the photo here is not how it's supposed to look. Again, no sign of bugs, and my tendency is to assume that we're overwatering, because there have been other plants that have had overwatering damage. (Catharanthus -- though nobody believes me when I say that's what it is -- and Ipomoea, as well as the Pelargonium addressed above. We're very worried about things drying out. More than we should be.) Though this is a different look, and so possibly a different problem. I'll get an ID for the plant today and post it at lunch, since I didn't note it at the time, but maybe people will have ideas anyway: The plant is a Cuphea 'Flamenco Samba.'

Twenty-something (Pedilanthus tithymaloides)

Pedilanthus tithymaloides is kind of a funny plant to research, since after you clear all the standard houseplant sites and plant sellers out of the way, what you are left with is a lot of scientific stuff that cannot be accessed without (expensive) subscriptions. So there's indication that a lot of work is being done on and with this plant . . . somewhere, but you, unless you have thousands of dollars to sink into subscriptions for publications like The Journal of Parasitology, have to make do with the abstracts, or sometimes even less than the abstracts.

So I know, for example, that Pedilanthus tithymaloides has been evaluated for use in controlling the organisms that cause malaria,¹ schistosomiasis, and tuberculosis. It's been looked into as a possible renewable fuel source. Medical science is exploring it as the source of interesting anti-inflammatory drugs, or as a general antibacterial / antimicrobial. It also does something people find interesting when it's deprived of water for a while, and papers have been written about how the leaves won't change from green to pink without daily temperature fluctuations.² And on and on in that vein.

In short, there seems to be general agreement that this plant must be good for something, or possibly many things, even, but at this point, in terms of confirmable information, we got bupkus. It'd be handy to come up with a use, since it's already invasive in India, and, you know, if it's going to grow itself without any help, it behooves us to find a way to use it all. We just haven't, you know, done that yet. (Or have we? Only the scientists know for sure. . . .)

So, like a lot of twenty-somethings, it doesn't yet know what it wants to do with its life, but no worries: it's still pretty. It'll get by.


The scientific interest mainly revolves around the sap, which is white and opaque and full of unusual compounds – granted, they're compounds produced so the plant can burn your flesh off,³ but we overlook that sort of behavior in a lot of other plants (for example, and another example, and a third example), so I see no reason to single out Pedilanthus tithymaloides⁴ for disapproval. As with these other plants, if you're doing some pruning or whatever, you'll want to use some common sense: take some basic precautions to keep the sap from touching your skin or eyes, and then if you get some sap on you anyway, wash it off.

Wikipedia, incidentally, makes the bold assertion "In Perú, it is called cimora misha and is sometimes added to psychedelic brews made from mescaline-containing Trichocereus cacti. Its pharmacology is unknown." So, wikiposedly,⁵ this is a psychoactive plant, but I suspect it's not a very good one if they 1) only use it "sometimes" and 2) the U.S. government still regards it as legal. But we can still, I suppose, add "psychoactive drug" to the list of things Pedilanthus tithymaloides maybe wants to be when it grows up, if it ever grows up.

Special Note to the stupid and/or impressionable: I do not recommend attempting to consume any part of this plant, by any means. I do not believe it is a psychoactive plant. I do believe it will probably hurt you. If you try this anyway, I accept no responsibility, and will point to this Special Note as evidence that I tried to talk you out of it.

My personal connections to this plant are mainly historical: I had one about ten years ago, when I was a twenty-something, that grew from a tiny little cutting into a mighty little shrub, and then eventually succumbed to . . . well, basically it succumbed to being ugly. I mean, ugly is why I got rid of it: it didn't have pests or rot or anything. The overarching reason is that I only had one north window in my apartment, and didn't always remember to water, and after watching the plant struggle with that for a while I was like, you know, I don't think this relationship is working out, so I chucked it. And then I moved, like, immediately, and wound up with a south window and no Pedilanthus, and realized I wanted one after all, and it took a good year and a half to track down another⁶ and I felt stupid.

So it's been nice to be reunited.

The main horticultural interest in the plant comes from its unusual habit: the stem changes direction each time it grows a leaf, forming a zig-zag pattern. This is the reason for the common name of "devil's backbone," though that seems a little presumptuous to me (where are the devil skeletons? The devil autopsies? The devil x-rays?). Another common name is "Japanese poinsettia," which makes about as much sense as calling French fries French or German chocolate cake German: the plant is actually a New World native.

Excitingly, part of its natural range is Southern Florida, which means that it probably isn't going to be a dangerous, ecosystem-wrecking invasive there like everything else seems to be. (Hawaii: you should still worry.)⁷ The leaves on variegated versions like mine also color up if grown in very bright light; when I bought it, the leaves were entirely hot pink with a green center, nothing whitish to be found anywhere. They then went cream/chartreuse for a time –


– and enpinkened⁸ again when I moved it to the south window.

They're grown outdoors in warm climates partly for the flowers, which occur in bunches at the end of a stem and are red and hummingbird-pollinated. Supposedly the flowers are bird-shaped, or possibly shoe-shaped, depending on who's doing the describing, but I haven't seen a close-up picture that's clear enough for me to see a resemblance to either one. (I also don't see that many bird-shoes or shoe-birds, which raises questions about the quality of the comparison in the first place.) This is, then, the story behind the other big common name, "redbird cactus," which makes about as much sense as calling the plant Bob, because the only part of that name that's true is "red," and that's only true when it blooms, which is not all the time.

There are a few cultivars (Oh! If anybody's reading this who has a cultivar other than the one pictured above, including the plain-green species, I would soooooooooo like to try to trade you something for some cuttings! Just FYI.). The species is plain green; I don't know if there's a particular name for the variety I have or not, though I've seen it referred to in a couple places as "P. tithymaloides variegatus,' so there may not be a variety name exactly. Glasshouseworks has the one I have, plus four others -- cupped leaves, smaller leaves, marbled stems, marbled leaves -- and Asiatica Nursery has two that they call 'Jurassic Park' and 'Jurassic Park 2.' (No word on whether they plan to make it a trilogy or not.) As always with Asiatica, I'm fascinated and intrigued right up until I see the price ($25 + shipping for a 3.5-inch pot!), and then I become significantly less interested.

Edited to add: I did eventually break down and bought 'Jurassic Park 2,' photos of which are located here, along with a review of Asiatica's service and so forth. 'Jurassic Park 2' does not appear to be a P. tithymaloides cultivar - the leaves are much too big and thick - but I'm not taking it out of the post because it's still a Pedilanthus (if anything is still a Pedilanthus, see footnote 4), and it's not likely to warrant a post of its own.

In any case. These are fairly easy, tolerant plants, though they do have a few non-negotiable needs.

Water: Plants can survive for a pretty long time without water; however, the only way this plant knows to communicate "Water now" is by dropping leaves, and it does that later than it ought to. This can be a good thing, if you're into the look this will produce: long bare zig-zag stems. I'm not opposed to the look myself, but for most people, you're going to want to hold on to the leaves, and in that case, you want to water only when the plant has just gone dry, not whenever you happen to notice that it's dry, because if you make it wait too long you will be looking at sticks.

Light: This is surprisingly negotiable, for a surprisingly long time, though if it's too dark for too long the plant will eventually start reaching for more light (if it's spring or summer) or stop growing entirely (if it's fall or winter), and then there'll be a point where every time you look at it, it'll be giving you big puppy-dog eyes and the idea will flit through your mind that maybe it should be euthanized or given to a good home or something. And then you will feel bad about yourself. So just give it good light from the outset. East or west window minimum, south preferred, and if it turns pink then you'll know you're doing something right. This is my own opinion, not that of the usual houseplant-advice places (which say bright indirect light indoors), but if you want it to turn pink I'm just about positive that you'll have to give it some sun, at least.

Humidity, Temperature, Grooming: All pretty much non-issues. Temperature, remember, is important because it's necessary for the pink color to show up (allege the scientists), but they seem to be capable of tolerating temperatures down to about freezing (and are hardy in zone 10, according to two different sources). Grooming is more or less limited to sweeping up dead leaves, and that only if you've been a very naughty waterer, though you'll get a bushier plant faster if you cut it back occasionally and plant the cuttings with the parent: they're reluctant to branch on their own.

Pests: I have never seen, or even heard of, Pedilanthus tithymaloides having a pest problem. That doesn't mean it doesn't happen, but it does mean that this is not a plant where you're forever going to be fighting bugs, like you would with spider mites and Hedera helix, or mealybugs and Cereus peruvianus (which, no, the situation with my Cereus is only barely improved: one plant seems to be better, the other still has them, and I just don't have enough time or Q-Tips to deal with this right now so I'm not sure what happens next.).


Feeding: I haven't seen anything specific about this plant needing any more or less fertilizer than your average houseplant. It does have a fairly marked dormancy in the fall and winter, when it doesn't do much, and I wouldn't bother feeding it then, but as long as it's in active growth, feed as normal, either every two or three months according to label directions, or half-strength twice as often.

Propagation: Propagation is easy, and basically amounts to just taking cuttings whenever the spirit moves you. Callus them by setting them aside for a day to dry (remember to avoid getting sap on anything you're going to want later), and then stick them in dirt. Or sand. Or damp perlite. Or water. Pretty much whatever's at hand. Rooting will be faster with some of these than with others (I'd favor regular potting soil, possibly with some perlite or vermiculite mixed in.), and it's better to do it in spring or summer than fall or winter, but it will eventually happen.

This is probably never going to be a major part of the tropical foliage industry: it's a little too dangerous, a little too needy, a little too weird (though I'm realizing, as I talk to more and more customers, that for any given plant, there's somebody out there who hates it, and somebody else who thinks it's the Coolest Thing Evah). But you will be seeing it somewhere, in large quantity, just as soon as it figures out what it wants to do with its life and settles into a career of some kind. Whether it's going to be a doctor, exterminator, drug-pusher, or some kind of alternative-fuel hippie, only time will tell.

-

Photo credits: all photos are my own.

¹ (Though it doesn't seem to be very good at it)
² Which changes in color also seem to be linked to the activity of an enzyme called peroxidase. Peroxidases are proteins which break down hydrogen peroxide (H₂O₂, the same stuff one disinfects wounds with, or bleaches hair with) into water and oxygen. Different species have differing peroxidases, but the need for something to split up hydrogen peroxide is a pretty universal need, and so peroxidases are found in plants, animals (including humans), fungi, and bacteria.
³ (Exaggeration. It can cause irritation, but it's not even in the ballpark of some of the nastier Euphorbias.)
⁴ Possibly now Euphorbia tithymaloides. It's not clear to me whether this is an official name change, but the same forces at work in renaming Synadenium grantii to Euphorbia pseudograntii would seem to be operating here, so I'm guessing if one changes, they both change.
⁵ I originally saw this "wiki-supposedly," but I don't remember where, and searching the net didn't turn it up. I think wikiposedly sounds better anyway. It would obviously be defined as,

wikiposedly \wi·kē·'pō·zəd·lē\ adv. 1 a Alleged to be true according to Wikipedia, though in fact untrue, 1 b unverifiable, or 1 c improbable.

⁶ In Ames, Iowa, at a weird organic-greenhouse-slash-antique-store previously mentioned in Clivia miniata. This is also where the Sansevieria trifasciata 'Bantel's Sensation' pictured at the bottom of this page came from. I would have gotten more plants, but 1) on that particular day, there was a big storm blowing into Iowa, and the husband and I were sort of racing the storm home, 2) I only had just so much money to spend on the trip and I'd used a lot of it already, and 3) there were some serious pest problems on some of the plants, including the single creepiest case of aphids I think I've ever seen. I mean, I'm all for organic growing and stuff, but given the choice between a raging insect problem and some pesticide, I'm going to go with the pesticide every. Single. Time. That said, props to the guy for having a lot of stuff there that I've either only seen for sale at his place, or I've only rarely seen somewhere else, and it was all more or less alive, so perhaps I just caught him on a bad week. Some googling turned up a place called Ames Greenhouse and Antiques, at 3011 S Duff Ave, Ames IA, 50010, which can be reached by phone at (515) 232-1332, and judging from the look of the map, I'm almost positive that this is the place in question. And if you check it out, tell them Mr. Subjunctive sent you. (Not that they know who I am, but it amuses me to think that someone might say this.)
⁷ (Explanation for newcomers to the blog: there are enough houseplants that have become invasives in Florida and Hawaii that it's somewhat of a running joke here. It's not actually funny: some of these really could do, or have already done, actual damage to wildlife. See also Asparagus spp., Sansevieria trifasciata, Syngonium podophyllum, Murraya paniculata, Tradescantia pallida, Epipremnum aureum, and Ardisia elliptica.)
⁸ Well, it ought to be a word. Though I might prefer empinkened instead. Haven't decided.