Potatoes produce toxic fruit! 

I'll assume we're all familiar with the humble potato tuber. This is the part that lives underground that some machine digs up to send to the store for us to eventually eat.  This part of the plant is actually a part of the root system. Its purpose is to store nutrients. That's why potatoes are so packed full of calories. Plus all that bacon, cheese, butter, and sour cream you're loading on top isn't helping either but it sure is awfully delicious. Anyway, the bushy plant above ground can die off over the winter but the tuber will then supply nutrients for the plant to re-grow in the spring, unless you dig it up and shove it down your gullet. This is also part of why potatoes have been so popular around the world, they are a high calorie food, they store well, and pillaging armies aren't so prone to dig up your potatoes when there is easier food to be found.

If you've ever left a bag of potatoes out you've probably noticed that they start to grow roots out of the little white spots that we call "eyes."  You probably also know those are new roots growing out of the tuber.  Commercial farms and home growers generally use old potatoes to grow new plants.  These old potatoes growing roots out of the eyes are called "seed potatoes."  Potatoes are pretty easy to grow.  You can take that seed potato and pop in the ground and there's a pretty good chance you'll see a green plant sprouting up within a few weeks.

I'm not going to go into actually growing potatoes so we'll skip a few steps here and get to the part where there is a full grown plant up out of the ground.  That bushy potato plant should produce flowers. Those flowers, if pollinated and environmental conditions are right, will then produce a fruit. The fruit is kind of like a tomato. A little green tomato about the size of a mature cherry. 

A Toxic Green Tomato Thing!

So, potatoes and tomatoes are both members of the Solanaceae family, the Nightshade family.  Typically, nightshade plants are thought of as poisonous, or at least certain parts of them are.  These plants may produce several toxic alkaloids but a common one is solanine. This stuff will put the hurt on you while you projectile vomit everywhere and spray out of your backside, it may even make you hallucinate at higher, possibly lethal, doses. Some other familiar nightshades include:

• Tomatoes
• Tomatillos
• Eggplant
• Potatoes
• Goji Berries
• Tobacco
• Peppers

The potato plant does what fruiting plants do, it produces flowers that become a fruit.  So why haven't you ever heard of the potato fruit? Why aren't you chopping them up for salads and guac and what not? You guessed it, because unlike some of its cousins the fruit of the potato is poisonous. So we just stick to eating the tubers instead. The leaves and stems are poisonous too, so don't make salad from them either.  That goes for tomatoes, and peppers, and eggplants, etc. There's actually a small amount of solanine in the potato tuber itself, but obviously it's rarely ever at levels high enough to cause harm.  In some rare instances potatoes left to dry up in the sun and then eaten have made people sick though.

What Is The Fruit Good For?

Well, fruits carry seeds.  So, he potato fruits holds "TPS" or True Potato Seed (not to be confused with "seed potatoes"). It's interesting the the potato plant has evolved poisonous fruits.  So many plants make edible fruit to encourage animals to eat and spread their seeds through their droppings. Yet the potato fruit is poisonous and we figured out to dig up their nutrient reserves from underground then selectively bred them for huge sizes. The mature potato fruit holds a few hundred seeds that can be saved and planted.  When a tuber is grown out it creates a clone of the parent plant through asexual propagation.  Your average Yukon Gold is a clone of a clone of a clone of a clone.... But, if you plant the potato seed then you grow out the mixed genetics of the mother plant and the pollinating plant. This tends to create a potato with different properties than its mother, sometimes they can be so varied that the resulting tubers seem like a completely different variety.

There are folks researching potatoes and cataloging the various varieties.  If you're interested to learn more about potato genetics, how to grow potatoes at home, and all the different cultivars please visit KenoshaPotato.com

Bonus Fact

Potato skins don't really hold all of the nutrients, your mom was wrong.  The skin and flesh both hold a lot.  The skins hold more of some and the flesh holds more of others.  Still though, be an adult and eat the skins.  Grill 'em up and burn 'em a little. Hit them with some olive oil and go generous with the salt and pepper, and whatever other spices you like. They're delicious.

Here is a fruit on one of my own backyard potato plants

I just started growing potatoes in the garden this season.  In doing my diligence and research I learned about the potato fruit.  It's not a given that the plant will make fruits.  Conditions have to be right for it and I'm happy to see that I have several fruited plants.  I'm looking forward to growing from seed next season.

Sources:

http://kenoshapotato.com/

http://www.diagnosisdiet.com/nightshades/

http://healthyeating.sfgate.com/skin-potato-really-vitamins-5378.html

https://en.wikipedia.org/wiki/Potato_fruit

https://en.wikipedia.org/wiki/Tuber

https://en.wikipedia.org/wiki/Solanaceae