If you’re celebrating Thanksgiving today, you’ll soon be having the annual argument about whether yams and sweet potatoes are different. They are. They really are. Sweet potatoes are dicots and closely related to morning glories (the vine with pretty flowers and hallucinogenic seeds). And yams are monocots, like grass. Yams are vines, too, by the way, and the original source of birth control pills (fyi, they don’t work if you just eat lots of them).
In case you slept through your evolution class, monocots and dicots diverged 150-200 million years ago — that’s during the Mesozoic, when dinosaurs were diversifying. A bonus fact to wow your family with is that neither yams nor sweet potatoes are potatoes, which are in the deadly nightshade family (wild potatoes, pre-domestication, are toxic). The phylogeny (“family tree”) based on their chloroplast genomes is shown above. There are, of course, lots of other plant species, but you should get the picture — sweet potatoes are grouped with kin-folk, and yams are grouped with their kin-folk. They look and taste a lot like each other but are completely different beasties. Yams are more expensive to produce, so sweet potatoes in stores are often labeled as yams. If you think you are eating yams today, chances are you’ve been duped. But with enough marshmallow and butter, you probably won’t notice.
Of course, if you kin-folk don’t accept an Old Earth or evolution, your conversation at the dinner table is probably going to be fundamentally different (so to speak). Can’t help you there.