It's an oddness of modern life that you can eat a food for years and never know what the plant it comes from looks like. You might not know if the fruit, vegetable or nut you're eating came from a tree, a bush or a root. You might not recognize it hanging right in front of you.

I had never seen a cacao plant until I lived in Hawaii — its dark brown seeds are ensconced within snowy-white, lightly sweet fruit, all packed neatly beneath a melon-like maroon exterior. Unless I'd been told, I never would have guessed what was inside. And despite sitting at my grandpa's knee as a child, picking out the mild, fatty cashews from the mixed nuts, I never knew what they looked like before they were harvested.

It wasn't until I was at a local market on Barbados six years ago that I saw what cashews look like right after being picked from the tree. When I learned how they grew, I finally understood why they are so expensive.

A fruit or a nut?

Cashews are native to Brazil, but they were exported to India in the 1550s and now are considered a traditional part of Indian cuisine. Cashews are grown all over the world, as the evergreen trees that produce them can be cultivated in a variety of tropical climates. Their deliciousness has long been appreciated by the Brazilian people, who eat both the nut and the "fruit," which, as you can see from the image above and in the painting below, hangs above the encased cashew.

Painted between 1641-1644 'Mameluca Woman under a Fruiting Cashew Tree' was created by Dutch portrait and still-life painter Albert Ekhout, who was one of the first European painters to travel to the Americas. (Photo: Albert Eckhout [public domain]//Wikimedia Commons)

I put "fruit" in quotes because the colorful red or yellow bulbs above each cashew (the true seed of the tree) is botanically known as an accessory fruit, pseudofruit or false fruit. It's not a real fruit at all. That's because, unlike an apple or a pear, it does not contain any seeds. Still, it's commonly called the "cashew apple" in English and can be eaten raw or made into jams or juice.

The juicy false fruit tastes like a cross between a mango and a grapefruit, though you're unlikely to have ever seen it in a supermarket because it has a very thin skin, which means it's difficult to transport.

Surrounding the part we like to eat is a double shell that contains three things we certainly don't want to eat:

phenolic resin, which can be used as an insecticide

anacardic acid, a serious skin irritant

urushiol, a substance related to anacardic acid that's also found in poison ivy

Cashews are related to poison ivy, by the way. They also share a family line with pistachios and mangoes, both of which contain urushiol in their skins or exteriors (but not in the edible part).

Once you properly roast or heat a cashew, the toxins are destroyed. So even if you buy raw cashews — which make a delicious milk, if you enjoy nut milks — they have been heated enough to be safe.

Following a heat treatment, the exterior layer needs to be removed and an interior hard shell must be cracked before you find the yummy, creamy, cashew interior. Check out the laborious process in this video; our ancestors must have gone through many trials and errors to figure this out.

A price to pay

It's due to the nature of this multi-step processing — and the fact that just one nut comes attached to each fruit — that cashews are pricier than other nuts. This isn't the only higher cost: there are plenty of human-rights abuses attached to cashew farming. Pair a high-value crop with the politics of developing countries and you get an unfortunate result. Telegraph writer Bee Wilson reports that some groups call them "blood cashews" for their link to mistreatment of laborers.

Remember the skin irritant? According to The Telegraph:

Many of the women [in India] who work in the cashew industry have permanent damage to their hands from this corrosive liquid, because factories do not routinely provide gloves. For their pains they earn about 160 rupees for a 10-hour day: $2.25. Conditions in Vietnam may be even worse than in India. Cashews are sometimes shelled by drug addicts in forced labour camps, who are beaten and subjected to electric shocks.

So as always, keep an eye out for the fair trade seal or organic certification when you are buying cashews, now the third-most consumed tree nut in the U.S. — and for good reason. Cashews are very high in minerals, especially magnesium, and like other nuts, have heart-health benefits if eaten regularly.