Yams or Sweet Potatoes?

I purchased yams last week to make Chipotle Mashed Sweet Potatoes. I became curious about the difference between sweet potatoes and yams; I figured there was some sort of variance but never really knew what it was. From what I found online, what I bought last week were not actually true yams but sweet potatoes. These two "flowering plants" are not related botanically, and most stores sell a variety of or two of sweet potatoes, with one of the varieties being tagged as a yam. The terms are often used interchangeably, but yams are less common in the US than sweet potatoes. Apparently, the USDA requires that produce labeled "yams" must also have "sweet potatoes" on the label.

A summary of the description of yams:

• starchy in taste, like a baking potato
• dry in texture
• the skin a brownish, almost black color
  
• non-tapered ends
  
• the flesh is usually off-white
• requires a year of frost-free weather before harvest
• most commonly available in ethnic markets
• Yam Dioscorea Species
  

A summary of the description of Sweet potatoes:

• sweet in taste
  
• more moist in texture
  
• can have a skin that is thin and smooth
  
• can have a yellow or orange flesh and can have slightly tapered ends
• requires 100 to 150 days to harvest
• some varieties remain firm when cooked; some soften. It is the soft variety that is often sold as a yam in the US.
• Scientific name: Ipomoea batatas

The potato in the second picture, based on the above descriptions, is a sweet potato. That is what I purchased last week from a bin that said "Yams $.99/lb."

In conclusion, you are most likely buying sweet potatoes at a typical grocery store, even if they are labeled yams. It seems not all stores adhere to the requirement to include the label "sweet potatoes" with the yam label. Or, I just missed that part when shopping.

An aside: I was doing internet searches for information and came across this picture on flickr that I think is captioned incorrectly. Someone also left a comment saying so, and I found the pictures above from the link in the comment. I believe the commentor is correct in saying the potato on the left in the photo is not a sweet potato but a yam.