Yams vs sweet potatoes?

They're the same thing!

They are completely different species........

http://homecooking.about.com/od/howtocookvegetables/a/sweetpotatodiff.htm

I know, but how do you tell?

From the link;

"Generally sweeter than than the sweet potato, this tuber can grow over seven feet in length.

The word yam comes from African words njam, nyami, or djambi, meaning "to eat," and was first recorded in America in 1676.

The yam tuber has a brown or black skin which resembles the bark of a tree and off-white, purple or red flesh, depending on the variety. They are at home growing in tropical climates, primarily in South America, Africa, and the Caribbean.

Yams contain more natural sugar than sweet potatoes and have a higher moisture content. They are also marketed by their Spanish names, boniato and ñame."

Yams are cheaper than sweet potatoes (in my area anyway), so I'm going to switch to yams! Either way they are my favorite "diet food" because they're soooo filling.

Aside from their color difference, to me yams do have a deeper and different kind of sweet taste (don't know how to describe it) and I prefer to eat them in a casserole or as a holiday yam dish. Sweet potatoes are my favorite to eat straight up with nothing added. Love them roasted, baked, and steamed.

A produce guy told me that American yams are just a variety of sweet potato.

According to wiki, that is mostly right.

Real yams apparently have a rough and scaly skin, whereas pretty much any "yams" I've seen in the US have the same skin as a sweet potato. From the Library of Congress' "Fun Science Facts" (http://www.loc.gov/rr/scitech/mysteries/sweetpotato.html):

Why the confusion?

In the United States, firm varieties of sweet potatoes were produced before soft varieties. When soft varieties were first grown commercially, there was a need to differentiate between the two. African slaves had already been calling the ‘soft’ sweet potatoes ‘yams’ because they resembled the yams in Africa. Thus, ‘soft’ sweet potatoes were referred to as ‘yams’ to distinguish them from the ‘firm’ varieties.

Today the U.S. Department of Agriculture requires labels with the term ‘yam’ to be accompanied by the term ‘sweet potato.’ Unless you specifically search for yams, which are usually found in an international market, you are probably eating sweet potatoes!

For what it's worth, I've always just seen "sweet potatoes" and called them that, and until recently I'd just thought yam was a synonym for sweet potatoes used mostly in the South. Since learning they were two separate vegetables I've occasionally looked for yams and not seen anything labeled as such. I also never saw the white ones until a couple of weeks ago when I accidently bought one at WF and freaked out when I peeled it, wondering it I'd accidently bought some weird potato instead. I looked it up, reassured myself that a sweet potato could look that way, and it tasted basically like a regular one. Next time I went to WF I checked and saw they were selling "white sweet potatoes" in addition to the regular kind.

In our grocery stores, the dark orange ones are labeled 'yams' and the near white ones are labeled 'sweet potatoes,' and that is how I log. Also, too me, when cooked, there is a subtle texture and taste difference.