I've been working on an article about the various Sweet Potatoes and the differences and it occurred to me how humorous the situation is. Anyone in food knows that what is called a Yam in most cases is actually a sweet potato. This is fairly common knowledge but digging further it only gets worse and it isn't just sweet potatoes who are violated in the arbitrary naming process of food.  

Rest assured there is a plant called a Yam and it is edible but most American's have probably not even seen one let alone eaten it.  <big word alert> The Yam is native to Africa and Asia and belongs to the monocot family Dioscoreaceae.  Monocots are one of two major groups of flowering plants (or angiosperms) that are traditionally recognized, the other beingdicotyledons, or dicots. Monocot seedlings typically have one cotyledon (seed-leaf), in contrast to the two cotyledons typical of dicots. So in short a Yam is a monocot and a Sweet Potato is a dicot - not even botanically related at very base level of flowering plants. So what you see in the grocery store called Yam is actually a Sweet Potato no matter what color it is. There are yellow Sweet Potatoes labeled as such, there are orange Sweet Potatoes labeled as Yams and there are purple Sweet Potatoes labeled however the person wanted who put up the sign. It gets worse.

In addition to a "grocery store Yam" being in fact a Sweet Potato it's not even a potato at all. The potato's scientific name - Solanum tuberosum reflects that it belongs to the Solanaceae family whose other members include tomatoes, eggplants, peppers, and tomatillos. That's right, you say potato, I say tomato! Potatoes are related to tomatoes and eggplants. There are over 100 varieties of edible potatoes and the Sweet Potato isn't even related because it belongs to the Convolvulaceae plant family and is known by the scientific name of Ipomoea batatas. What's interesting about all of this is the genus is ipomoea and the species for Sweet Potato is batatas ie. phonetically potato which tells you how far back the confusion goes. Anyone who's seen a Sweet Potato flower may recognize it as another close relative in the same botanical family is the "Morning Glory" flower. <end of big word alert> 

To recap:

• Yams are Sweet Potatoes
• Yams are not yams
• Sweet Potatoes are not potatoes
• "Sweet" Potatoes have a lower Glycemic Index than potatoes
• Potatoes are related to eggplants
• Eggplants do not make eggs (irrelevant)
• Sweet Potatoes are related to Morning Glory
• Real Yams do exist and they're not from Miami (you'll understand in a minute)

So Yams aren't yams, they're sweet potatoes which aren't potatoes and aren't sweet? Pretty much. How did this happen?

The history of the Sweet Potato in my own words:

1. 750 BC an unknown Peruvian digs up a root and starts gnawing on it. Sweet Potatoes become a big hit spawning massive population growth, a couple of ruthless rulers, a box with a diseased feather and some really unruly metal clad illegal immigrants who have very little respect for local customs of ownership but I'm getting ahead of myself.
2. A man from Italy wants to go boating but doesn't have the means to purchase one so he turns to begging which proves successful. He immediately gets lost in his new boat and about a month later runs it into a mound of dirt. Hungry he digs up a root and gnaws on it to much delight.
3. The local Taino people who were of course overjoyed to have been finally discovered told the Italian boater that the root was called batatas. 
4. Not having heard of a batatas  and having a slight hearing and/or comprehension problem he erroneously called it patata (you know from the rhyme potato, patata). Since the nice couple who loaned him their boat were Spanish this became the Spanish name for batatas. 
5. Later the English not paying much attention to anything on the stranded side of the English Channel renamed it potato. Keep in mind there wasn't such a thing yet so you have to give them some credit for their originality.
6. One hundred years later another man (who due to his lack of accomplishments remains unknown) dug up another root in South Columbia (I mean America, don't get me started) drags another tuber back to Europe. It resembled the batatas but generally lacked flavor or any other discernible value so it was given to the Irish and named potato.
7. Since people then named things by shape nobody noticed that the tasty batatas and the untasty potatoes were not in fact related nor did it matter - they were similar in shape so too should be similar in name.
8. One hundred years later some well meaning folks needed to get some shit done and since it was a bit early in the timeline to run by Home Depot for good hard working laborers they asked the Portuguese if they knew of anyone who might want a job where pay wasn't an object. They did and offered to provide the transportation. 
9. The newly arrived people were famished and upon taking into their site the aforementioned roots responded with the Wolof word  "nyam" loosely translated as "If you don't give me something to eat I'm going to open up a can of Chris Rock on you".  As a side note the same people used to say nyam back home followed by feverish gnawing on roots as well.  Food is once again named by shape. Do not confuse nyam with Miami which although has a similar amount of dirt and clingy things attached to it differs in shape on the southern end.
10. Zoom forward another 100 years (thankfully history happens in nice round numbers) to the deep south when orange colored sweet potatoes were introduced. The folks there didn't want to confuse anyone by competing fairly so they decided to rename orange sweet potatoes to  "If you don't give me something to eat I'm going to open a can of Chris Rock on you" but that was voted down in favor of Yam, an Anglicized version of the Wolof word nyam. Miami doesn't factor in here so we'll skip it for now.
11. Fast forward to another nice round number in history and you have the USDA whom with good intentions tries to rectify the naming situation and passes regulations to force everyone to put the name Sweet Potato on every box of Yams. They failed to define the size of the text thus a new industry was born for super small typesetters.