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If you’re ever vacationing in the Flamingo section of Everglades National Park in Florida, beware of the apples. In fact, if you’re pretty much anywhere from northern South America to Florida, including the Caribbean and Galapagos Islands, and you see a tall tree growing near water with yellowish-greenish crab apple-looking fruit, it’s probably best to keep your distance.

The fruit might be delicious, but it could also be deadly. Because that tree might be a Manchineel — which, according to the folks at Guinness World Records, is the world’s most dangerous tree. Every part of the Manchineel is toxic.

The sap in its wood and leaves can cause blindness and blistering, its fruit can cause boils in the mouth and throat as well as severe intestinal damage that can kill you. It’s no wonder Spaniards gave it the nickname “la manzanilla de la muerte”, or "little apple of death.” The tree contains a number of toxins, but the worst is probably phorbol. Or, I should say, phorbols. “Phorbol” refers to a family of related organic molecules that have two terpene chemical groups.

And they’re similar to compounds you have in your body — which is a bit of a problem. See, phorbols mimic the action of diacylglycerol — a fatty molecule your body uses in a number of ways, including to activate an enzyme called protein kinase C, or PKC for short. PKC is a pretty big deal because it regulates things like cell growth and metabolic activity.

So when phorbols over activate PKC, cells will increase their expression of genes involved in inflammation and cell death. This leads to a range of nasty effects like blistering and ulcering. Manchineels have phorbols everywhere, which is why you shouldn’t touch any part of them.

Oh, and here’s a not-so-fun fact: Phorbols are very soluble in water, so it’s not a good idea to stand under a Manchineel when it’s raining, either. Which, you know, it does in places like the Everglades. A lot.

What’s not entirely clear is why this tree went so overkill on the toxicity. It may be that, since the Manchineel typically grows in areas where there are lots of other toxic plants, it has such overdeveloped defense mechanisms to stay competitive. And it can get away with having toxic fruit because it doesn’t need animals to spread its seeds.

It lives by the ocean, so its fruit can bob along on the waves to move to new lands. Though, it may get more love from critters than you’d think. Some reptiles seem to eat the fruit with no ill effects, and black spiny-tailed iguanas will even live in the trees!

How remains a mystery. And even our species doesn’t always keep away. Because the trees live in places like Florida where there are a lot of strong winds — and, you know, hurricanes every so often — their wood is really hard.

So cabinet makers love it. Though, they have to carefully cut and dry the planks for several days to let the phorbol-laced sap evaporate out. And the trees aren’t just hard — their deep roots and thick branches help protect coastlines from damaging winds and waves.

That means, while they might be toxic to touch, they help protect us and coastal ecosystems during storms. So if you do see a Manchineel while you’re strolling along the beach, you can smile and appreciate all that it’s doing for the plants, animals, and people who live nearby… and then give it a wide berth. Thanks for watching this episode of SciShow!

Fun, educational science videos like this one are what we do, but we can’t do it without the help of our patrons on Patreon. If you want to learn more about joining our awesome community of patrons and how you can help support the work we do, you can head on over to Patreon.com/SciShow. And if you want to learn more about poisonous plants, you might enjoy our list of nine that might be around your house right now!

Some of them are quite surprising. [ ♪OUTRO ].