There is a lot of confusion over potatoes. With hundreds of varieties available to growers and dozens if you shop at a farmers' market, you might feel like you need a cheat sheet to navigate your way through which varieties are best for which dish.
Even at an average supermarket, there are usually at least five varieties of potatoes. Most of us know which one to get for a baked potato (test: what's it actually called?) and most know what a sweet potato look like (wait, yam? sweet potato? which is it?), but beyond that, selecting the right potato for the right dish remains a mystery.
Those with a high starch content, like Russets, are great for baking and frying. Because of their starch, they don't hold together very well but are absorbent so are best paired with something to absorb (think butter and sour cream.) They are decent mashed, but care must be taken not to over work them, else you'll have a gluey mess. A starchy potato excretes a milky film onto the knife when sliced. 
Those with a less starch, like most red-skinned potatoes, have a more waxy texture so they hold their shape while cooking. They work well for dishes like soups, stews, potato salad and scalloped potatoes where you would need to boil, slice, or roast. You can usually determine if a potato is waxy by its thin skin. If the skin feels very thin to the touch and you can easily scratch off a piece (don't do this before buying it!), it's probably waxy.
A third category would be medium starch potatoes which are more all-purpose, and they'll work in most potato dishes. Yukon Golds are a commonly available all-purpose potato.
Beware of new potatoes! I recently found out that I'm particularly sensitive to the alkaloids in potato (mildly poisonous, they give that weird bitter, metallic-in-the-back-of-your-throat taste often found in greenish potatoes).
I've had frequent problems eating red potatoes, so I avoid those, but over the weekend I bought some baby russets at the farmer's market, and basically made myself sick all night. Yech. Just wanted to share so others could learn from my misfortune.
(Potatoes that actually look greenish - of any type - also are high in alkaloids.)
view marisab's profile
It's like a potato photo-lineup! Actually, the photos could make a really cute calendar.
view Michelle of Montreal's profile
Technically all yams that you buy in this country are sweet potatoes, just different varieties. True yams are grown in the sub-tropics and they are larger than your arm.
view charise's profile
Sara--such a great job at describing the characteristics of potatoes... I couldn't have said it any better! BTW--Meredith from the US Potato Board Here :-) Cant wait to see what you find out about the 16 varieties you picked up.
If your readers are looking for new ways to prepare those awesome spuds, feel free to take a look at our new on-line resource (a dinnertime site designed for moms) www.Momsdinnerhelper.com. We also offer prizes for submitted recipes, too!
In response to marisab--she's right that potatoes with a green hue contain solanine, an alkaloid that if eaten in large quantity could give you a stomach ache. It's a naturally occuring chemical produced by vegetables that have been over-exposed to light (some stores will put an opaque tarp over the potato display to block the light). But never fear--if some of your potatoes are turning a little green, just peel the skin off and if the flesh is white, they're perfectly fine and super-nutritious to eat!
view Meredith Myers's profile
Although it's possible to get yams in this country on occasion (these will invariably be either flour or already cut up, since a true yam is enormous), generally Americans buy sweet potatoes and erroneously call them yams. The sweet potato is not botanically related to the yam. A yam is actually the tuber of certain tropical plants in the lily family, whereas the sweet potato belongs in the same family as morning glories. Neither the yam, nor the sweet potato, is actually related to potatoes.
The reason (theory) "yam" is a synonym for sweet potato in the common vernacular is that during the slave days, slave cooks believed they were similar (and they are similar in some ways) to what they called "nayami," or yam. Over time, this mislabel of the sweet potato became a commonality.
view seidhr's profile