Houseplant Toxicity Week: Part 3 (Dangerous Plants)

If you have landed on this page because you are concerned about a child or pet who has eaten a plant, seek emergency medical help. In the U.S., you can call Poison Control at 1-800-222-1222 (for children), the ASPCA at 1-888-426-4435 (for pets; $60 consultation fee applies), or the Pet Poison Helpline at 1-800-213-6680 (pets; $35 fee applies).

Part 3 of a seven-part-and-two-appendix series. (Part 1) (Part 2) (Part 4) (Part 5) (Part 6) (Part 7) (Appendix 1) (Appendix 2 - Index) For part 3, we're looking at plants which can cause serious and possibly permanent injury requiring hospitalization, or extreme and prolonged agony, or whatever, but which for whatever reason usually don't result in an actual fatality. Like Celine Dion: agony, sure, but she hasn't killed anybody.¹ Agave assortment from work. Agave spp. (century plant) (A. victoriae-reginae) Although people have found ways to eat Agave spp. over the course of history, they generally have to be cooked or fermented first. The leaves contain calcium oxalate² crystals, which leads to irritation, burning, swelling, and so forth, if chewed. The leaf fibers are indigestible, and may block digestive tracts if eaten in large quantity, and yes, this actually has happened. The main kid/pet danger is the spines, which are in fact very sharp, and which whenever I've accidentally stabbed myself with an Agave have always left a spot that hurt and itched and throbbed for hours afterward. I don't think kids or pets eating the plant is nearly as big of a worry, just because I can't see how that would be possible without running into the thorns first. But some kids and pets are more stubborn than others, too, I suppose. Albuca bracteata, or "pregnant onion." The nearly-perfect heart shape from the leaves and pot was unplanned. Albuca bracteata (pregnant onion) Pregnant onion was previously known by the names Ornithogalum bracteatum and O. longibracteatum. The other Albuca and Ornithogalum species are not common as houseplants, though O. umbellatum is sometimes sold around Easter as Star of Bethlehem,⁶ or more amusingly as "dove's dung." The warnings from Toxicity and Handbook only refer to O. thyrsoides, O. caudatum, and O. umbellatum, but I believe it's likely that Albuca bracteata is also dangerous. After ingestion and a symptomless period of a few hours, the symptoms begin: the more serious of these include changes in blood chemistry and heart rhythm. Some species also have calcium oxalate crystals in the sap, which can cause irritation, burning, etc., as with many other plants. It looks like the foliage is the least dangerous part of the plant: bulbs and flowers are more dangerous. Amaryllis spp. (amaryllis) As for Hippeastrum spp., q.v.

Bowiea volubilis (climbing onion) Cases of poisoning are rare, since this is not a commonly cultivated plant, but the entire plant contains cardiac glycosides like digitalis ("foxglove") and should be regarded as dangerous to humans and pets.

Cestrum nocturnum (night-blooming jasmine, night-blooming jessamine) Uncommon indoors, but not unheard of. A lot of stuff about this one is mysterious, or disputed: it's unclear whether the ripe berries are safe to eat (the unripe berries are decidedly not), or what the toxic component of the plant might be (one of my sources said atropine and similar compounds, like in Datura and Brugmansia: see the Crazy Super Dangerous list). The plant is uncommon enough that actual human or pet poisonings are not well documented, but the plant is known to kill livestock on occasion, so it's worth being a bit cautious. Toxicity also reports that some people react badly to the strong perfume from the flowers (nausea, dizziness, nose and throat irritation). Crassula ovata. Admittedly not a good picture for trying to comprehend the overall shape and habit of the plant, but I thought it was pretty. And it's not like you can't see overall-shape-and-habit pictures a gazillion other places on line if you really want them. Crassula ovata (jade plant) [written 7 May 2021:] I originally had this listed as safe, because the first time I looked into it (back in 2009), I didn't find much of anything about it that made it sound bad, and most of the on-line lists I encountered listed it as safe. Apparently we've learned something in the twelve years since then. Although it's still not particularly bad for humans -- mostly skin irritation, with a few people having allergic-type reactions -- it's considerably more of a problem for pets. I didn't find evidence that jade plants could kill pets, but 1) I didn't look all that hard, and 2) the effects I did find are bad enough that it's not hard to imagine that if a pet ate enough, or was in not-great health to begin with, it could cause death. So I was left kind of unsure which category to put jade plants in. "Dangerous" is possibly excessive, but I decided better safe than sorry.

Cryptostegia madagascariensis (Madagascar rubber vine) Contain toxins similar to those of Digitalis (foxglove); humans, dogs, and cats are almost certainly affected. Other animals may or may not be, but I wouldn't risk it.

Cycas revoluta (sago palm) Contains a light carcinogen, a neurotoxin, and a few poisons specific to the liver. Though sago flour is eaten in parts of its native range, it is processed first (usually by grating and then washing repeatedly with water), and children are not allowed to participate in the processing or eat much of the finished product. Ingestion leads to violent vomiting, diarrhea, headache, dizziness, paralysis, liver damage, and so on and so forth up to coma and death. Which you have to wonder how desperate for carbohydrates people would need to be to resort to this plant, and all the additional labor and risk it entails, just for some starch. Said to be particularly toxic to dogs and children.

Dieffenbachia 'Tiki.' Dieffenbachia spp. (dumb cane) Deeply unpleasant; theoretically lethal. Click the link for the history and gory details.

Euphorbia bougheyi variegata Euphorbia spp. are nasty in general, though I didn't find anything about this one specifically. Use eye protection when pruning, wash up carefully (and soap up repeatedly) after contact with sap, don't ingest the sap, etc. The whole genus, with the exception of the poinsettia (E. pulcherrima), which I'm going to write a full big post just for pulcherrima by itself, should be regarded as unsafe around kids and pets unless special precautions are taken to ensure that the plants are not top-heavy, cannot be accessed by kids or pets, and so on. The Amateur's Digest advises not having Euphorbia spp. in an area where "those . . . who like to help themselves to cuttings" can get at them. Personally? I can only feel just so bad for someone who hurts themselves while trying to steal. If you know one of those people is coming over, go ahead and leave the Euphorbias out for all I care. Maybe next time they'll ask.

Euphorbia drupifera (giraffe tree) As for E. trigona, q.v. Sap is said by The Amateur's Digest to be "very dangerous," though they don't give any terribly scary specifics, and elsewhere on the page they don't make a distinction between latex (from rubber, Hevea brasiliensis) and latex (from Euphorbias), which lowers my respect for them a bit.³ E. drupifera is also sometimes used as the base for grafted Euphorbias, which (if you'll permit me to speculate irresponsibly for a moment) might increase or decrease the overall toxicity of the graft.

Euphorbia grandicornis (left) and a NOID I think is probably E. pseudocactus (right). Euphorbia grandicornis (cow horns) Sap is reputed to cause blistering on the skin of some individuals. All desert Euphorbias seem to be at least theoretically capable of causing extremely painful eye irritation as well. E. grandicornis also has ginormous and sharp thorns, which are worth watching out for. I wouldn't recommend this for a home with pets or kids unless one had a really secure spot that only adults could reach, and use a heavy clay or ceramic (clay would be better for the plant) pot that would keep it from falling over easily. It pains me to say this, because I lurve my grandicornis. But they're not cuddly.

Euphorbia lactea (candelabra cactus, dragon bones, hat-rack cactus) As for E. bougheyi variegata, q.v. May be more dangerous to dogs than some, but it might also be the case that it was only ever checked in dogs: my source for this was not very detailed.

Euphorbia milii (crown of thorns) I didn't find a lot about this one specifically, but it's a Euphorbia, so repeat all the warnings from E. bougheyi variegata, and then add to that that the thorns are big and abundant and nasty.

Euphorbia pseudocactus As for E. grandicornis, q.v.

Euphorbia trigona Euphorbia trigona (African milk bush, African milk tree) As for E. bougheyi variegata, q.v., plus: I don't get the impression that this is considered one of the more dangerous Euphorbias, but it's dangerous enough that pets (especially) and children might be at risk from it. What often E. trigona often does do, that other Euphorbias may or may not, is it has a tendency to become very top-heavy with time, and top-heavy + thorns + sticky, irritating, copious sap = potential hazard.

Hedera canariensis (Algerian ivy) Ingestion of large amounts can cause the usual gastrointestinal symptoms (nausea / vomiting / cramps / diarrhea). In humans, it's fairly common for people who handle Hedera spp. a lot to develop allergies eventually: rashes, redness, and streaking from allergies develop and then typically take weeks to subside. There's much less information about what happens if plants are eaten, but the berries are known to be poisonous, and to cause a burning sensation in the throat, and in some cases where berries or leaves were swallowed, rash, rapid heartbeat, mental confusion, fever, and convulsions were observed. Ingestion will likely put you in the hospital; could be fatal to pets.

Hedera helix, assorted cvv. Hedera helix (English ivy) As for H. canariensis, q.v.

Hippeastrum spp. (amaryllis) Ingestion by humans leads to nausea, vomiting, salivation, diarrhea, cramping, dehydration, etc. Rarely fatal but can require hospitalization, mainly to treat the dehydration and electrolyte imbalance that goes along with diarrhea. I could not find anything specific about animal toxicity but assume that it is probably more or less the same.

Hydrangea macrophylla buds. The flower buds of Hydrangea are more toxic than the plant overall. Hydrangea macrophylla (hydrangea) Florists and others who work with the plant a lot have developed skin sensitivity to Hydrangea, but this doesn't appear to be common. Ingestion is a bigger risk, because the plant contains cyanogenic glycosides. ("Cyanogenic glycoside" translates from the scientificese as, roughly, "something that your digestive system will turn into cyanide."⁴) Severity of symptoms varies wildly, because plants differ wildly in how much of the toxin they contain, but, after a symptomless period of a few hours, one sees abdominal pain, vomiting, sweating, difficult breathing, blue skin, etc. In animals, the symptoms are basically the same, though the blue-skin part may or may not be obvious. Coma and death have been seen with some plants containing cyanogenic glycosides, but it's unclear to me whether Hydrangea is one of these: Toxicity says it's not, and Handbook says it is. Either way, expect to spend some time in the hospital.

Ledebouria socialis (silver squill) It took a long time to find anything specific about this one way or the other: I suspected it was dangerous but couldn't confirm it until I saw a commenter at davesgarden.com talking about how s/he believes that her cat had been eating it and then died of kidney and liver failure. One anecdote by itself wouldn't ordinarily be enough for me, but since it's all I've been able to find, the circumstantial evidence from the story sounds pretty solid, and I kind of suspected the plant was poisonous in the first place, I'm putting it in the Dangerous list.

Lilium longiflorum (Easter lily) This is usually not kept as a long-term houseplant, but is just brought in temporarily around Easter as a blooming plant and then discarded. So exposures tend to be few and far between. Neither of my main references (Toxicity or Handbook) mention Lilium, but there's widespread agreement on-line that it is especially dangerous to cats, and in fact it's kind of the quintessential dangerous-to-cats plant. WCW believes that she may have lost a cat because of an Easter lily, some time ago. There's basically no solid information out there about how much danger Lilium pose to humans or non-cat pets, but based on other plants in the Liliaceae, and the known danger to cats, I would treat them as though potentially lethal to everything.

Mandevilla spp. (Dipladenia) I was unable to find anything very specific or authoritative-sounding, but by association with the rest of the Apocynaceae (Plumeria, Adenium, Nerium, etc.), I'd expect Mandevilla has the potential to kill children or pets, or at the very minimum make them very ill.

Nandina domestica (heavenly bamboo) All parts of the plant are toxic to children, cats, and dogs. A lethal dose is possible, though I don't get the impression that this happens very often. Birds can eat the berries without harm.

Narcissus cv. Narcissus spp. (daffodil, narcissus, paper-white) Poisonings usually occur when bulbs are mistaken for shallots or leeks or whatever. Ingestion sounds extremely unpleasant.⁵ It is unclear whether the foliage is dangerous on its own: Handbook and Toxicity agree that the bulbs, and specifically the outer layers of the bulbs, are the most dangerous. It is also dangerous to handle Narcissus bulbs in large quantities over a long period; many occupationally-exposed individuals develop some kind of skin irritation, and a few of them become genuinely allergic.

Pachypodium geayi / lamerei (Madagascar palm) As for Mandevilla spp., q.v., but Pachypodium also have fairly sharp spines, which can pose a mechanical danger even if the plant is not toxic. I found no accounts of actual poisonings, though I believe I ran into some when I was working on the Pachypodium profile and just couldn't locate them again.

Pedilanthus tithymaloides. A really huge one, seen from overhead. Pedilanthus tithymaloides (redbird cactus, devil's backbone) The biggest danger from Pedilanthus appears to be skin irritation, which can be "very severe" according to Handbook and may cause blistering according to Toxicity. The sap will also severely irritate the eyes, like for Euphorbia spp., though it's maybe not quite as horrific (which, it should be noted, doesn't mean it's safe or fun or even bearable). Supposedly in the West Indies, a few drops of Pedilanthus sap is purposely added to milk and then drunk in order to induce vomiting, which raises all kinds of questions for me, most of which begin with "why?" Otherwise, if ingested, the plant causes the usual problems of nausea, vomiting, cramps, and diarrhea, more or less like you'd expect.

Philodendron 'Autumn.' Philodendron 'Autumn' Philodendron spp. contain calcium oxalate crystals, which cause burning, swelling, and pain in the mouth if chewed. To a lesser extent, they cause skin irritation, particularly in people who have to handle them in large quantities over long periods, occupationally. Humans do not appear to be much at risk from Philodendron spp.: it may hurt a great deal, and the affected tissues may swell a lot, which can be indirectly dangerous, but it does not seem to be the case that any humans have ever died due to Philodendron exposure, or that anybody has had any serious or long-term injuries either. The same holds true for most pets as well. That said, cats do appear to be more at risk from Philodendron than most species, and a number of feline fatalities have been reported. If you have both a cat and a Philodendron, and the cat has coexisted with the plant for a long time without ever trying to eat it, then I really wouldn't worry about it that much. Some cats are much more inclined to chew plants than others. However, if you already have a cat, I wouldn't advise you to get a Philodendron, and if you already have a Philodendron, I wouldn't advise you to get a cat.

Philodendron bipennifolium (sometimes P. panduraeforme; fiddle-leaf philodendron, horsehead philodendron) As for P. 'Autumn.'

Philodendron 'Imperial Red' As for P. 'Autumn.'

Philodendron 'Congo Green' As for P. 'Autumn.'

Philodendron 'Congo Red' As for P. 'Autumn.'

Philodendron 'Florida Beauty' As for P. 'Autumn.'

Philodendron gloriosum. Philodendron gloriosum As for P. 'Autumn.'

Philodendron hastatum As for P. 'Autumn.'

Philodendron hederaceum. Philodendron hederaceum (sometimes P. scandens, P. micans, P. oxycardium, P. cordatum, etc.; heart-leaf philodendron, 'Brazil') As for P. 'Autumn.'

Philodendron "Moonlight.' Philodendron 'Moonlight' As for P. 'Autumn.'

Philodendron 'Pink Princess' As for P. 'Autumn.'

Philodendron 'Prince of Orange' As for P. 'Autumn.'

Philodendron selloum (P. bipinnatifidum; tree philodendron) As for P. 'Autumn.'

Philodendron 'Xanadu.' Philodendron 'Xanadu' As for P. 'Autumn.'

Scilla spp. (squill, star hyacinth) As for Ornithogalum spp., q.v., but more so. Scilla poisoning gets described a lot more specifically, and appears to be a bigger deal. Both of my primary sources compare it to Digitalis poisoning, which if you know anything about Digitalis poisoning, you know Scilla is not to be fucked with. Expect hospitalization; human fatalities appear to be rare or nonexistent.

Solanum pseudocapsicum (Jerusalem cherry) Generally regarded as very poisonous, despite a lack of actual information: neither Toxicity nor Handbook have much to say about this plant. What symptoms have been documented primarily affect the heart and gastrointestinal system.

Synadenium grantii. I regret not getting a better photo. Synadenium grantii (African milk bush, African milk tree) Sap from Synadenium spp. is similar to that of Euphorbia spp.,⁷ and has similar effects. Avoid contact with eyes at all costs. Skin contact may lead to blistering, redness, pain, etc., and for some people, the reaction is delayed, so it's good to make a habit of washing up pretty thoroughly after contact. One case study reported in Toxicity of Houseplants, of a five-month-old who may have eaten part of a Synadenium leaf, resulted in repeated vomiting, redness and swelling in the face, drooling (though I don't know how you tell pathological five-month-old drooling from normal five-month-old drooling), loss of appetite, fever of 103F/39C, rash, and blisters.

Zamia spp. including Z. furfuracea, Z. integrifolia, Z. pumila (coontie palm, cardboard palm) All parts of the plant are poisonous, though (like with Cycas revoluta, q.v.) it can be eaten if prepared in certain ways. Handbook claims that Zamia spp. was a commercial source of starch until the 1920s. In order for that to work, of course, you have to know how to prepare it, which probably you don't, and your pets and children certainly don't, so it really doesn't even matter that it can sometimes, under very special conditions, be eaten. Symptoms of poisoning are the usual gastrointestinal vomiting and cramping, though some people have fallen into a coma. This is likely very dangerous to pets and children.

Zantedeschia (aethiopica?) NOID. Zantedeschia aethiopica (calla lily) Like other members of the Araceae, contains calcium oxalate needles throughout all parts of the plant, and is very painful if chewed. Handbook lists nothing beyond that, but Toxicity says that there are anecdotal reports of death, in children who tried to eat the flower's spadix. I don't know whether to believe this or not, but if it's good enough for Toxicity, it's good enough for me.

- Photo credits: All my own. Some are recycled, some are new.

¹ (As far as we know.) No, actually, I don't have anything huge against Celine Dion. I got pretty sick of that damn Titanic song when it was big, ten years ago or whatever, but that's only sort of her fault. I also have no particular urge to run out and buy her greatest hits album. I guess you could say that I'm mostly just kind of indifferent.

² (For those who have been reading along as these get posted: are you getting the impression that everything contains calcium oxalate needles? If not, I can just about promise that by Part 5, you will be.)

³ The word "latex" is sort of a general term for any white, milky sap, whether it contains rubber or poison or just happens to be white and milky. When people talk about "latex allergies" they mean allergies to the residual protein in latex rubber, which is derived from the rubber tree (the real rubber tree, Hevea brasiliensis, where rubber comes from, not the pretend rubber tree, Ficus elastica. Ficus can be used to make a really low-quality rubber, but in practice nobody does this because it's, you know, low-quality.). People who are allergic to Euphorbia latex are not necessarily allergic to Hevea latex, and vice versa, and it annoys me that people threw in completely unrelated and misleading stuff about Hevea latex rubber allergies in the middle of information about Euphorbia just because the sap of both happens to be white and milky.

⁴ More precisely, "a sugar, cyanide, and other molecule linked together in such a way as to produce cyanide when acted on by digestive enzymes."

⁵ Although any list of symptoms including "diarrhea" is bad, Narcissus poisoning often gets especially dire-sounding intensifying adjectives. Toxicity uses "copious diarrhea" and "profuse diarrhea," among a variety of unpleasant other symptoms, and wisely counsels the reader not to store Narcissus bulbs in kitchens or pantries where they might be mistaken for food bulbs.

⁶ Though of course, the Star of Bethlehem is part of the Christmas story, not the Easter story, so this doesn't really make a whole hell of a lot of sense. Silly, culturally illiterate florists.

⁷ In fact, when I was writing the profile for Synadenium grantii, I found some sources that claimed that it had been reclassified as a Euphorbia species. I tend not to believe this, but one never knows.