As a Brit having read an article: ‘is a yam a sweet-potato?’ I was left confused. Is a sweet-potato a yankee name for a parsnip? Is this just another difference in language across ‘the pond’?
Rob. 
A parsnip (here in the US) looks like an off-white carrot. A sweet potato has orange flesh, an orangy-brown exterior, and is shaped like a slightly pointy-ended regular potato. It’s frequently (incorrectly) referred to as a yam by us Merkins. (Yams are Old World plants, also with starchy tubers, but not as sweet; sweet potatoes are a New World thing, IIRC.)
Well, it’s not exactly “incorrect.”
from m-w.com:
Main Entry: yam
Pronunciation: 'yam
Function: noun
Etymology: earlier iname, from Portuguese inhame & Spanish ñame, of African origin; akin to Fulani nyami to eat
Date: 1657
1 : the edible starchy tuberous root of various plants (genus Dioscorea of the family Dioscoreaceae) used as a staple food in tropical areas; also : a plant producing yams
2 : a moist-fleshed and usually orange-fleshed sweet potato
If you’re gonna be that nit-picky about it, then white potatoes shouldn’t be called “potatoes” because they’re members of the nightshade family, unlike the “sweet” potato, which is in the morning glory family. The sweet potato was the original “potato.”
Us Merkans tend to refer to all those orange-y potato-like objects as either “yams” or “sweet potatoes”, depending on our socio-economic and geographic origins, regardless of botany.
For purposes of cookery, they are purt near identical, anyway.
And no, “parsnip” is never used to mean a yam or sweet potato–parsnips look like white carrots, quite different from the large bulbous orange-y potato-like object-ness of yams/sweet potatoes, and even people who never eat parsnips never mistake them for yams/sweet potatoes, and never use the word “parsnip” to refer to yams/sweet potatoes.
It’s not particularly an American thing, webcabbage. You’ll have worked out from other people’s posts that what thay call a parsnip is the same as what we call a parsnip and both yams and sweet potatoes are available from your local Tesco, as a search on this site will show (you’ll need to register first).
These last two are pretty similar vegetables in my experience, although the flesh of yams tends to be firmer, starchier and a darker orange. If you roast them, sweet potatoes do taste a bit more like parsnips than yams do.
Related question: Is a “kumara,” referenced in Aust/NZ cooking, also a sweet potato? The receipes I’ve seen would seem to indicate so, but I would like to know if it’s a slightly different vegetable, or exactly the same.
Yep. Same thing.
Just for the record, sweet potatoes in the US are erroneously called yams. Yams and sweet potatoes are not even related. Most North Americans have never seen a true yam. And there are dozens of kinds!
:rolleyes: For the record, my grocery store sells both sweet potatos and 3 kinds of yams. We call them either yams or sweet potatos not out of ignorance, but just because for cooking purposes they are pretty much the same. If I feel like making sweet potatoes I’ll buy whichever are on sale for the cheapest.
A slight hijack- before the arrival of the potato families from the new world, parsnips were used in England in the way that potatoes are now- the starchy filler part of the meal.
Most yams are not sweet, so if you substituted them in a sweet potato recipe, it wouldn’t be very good. For cooking purposes, they are pretty different. You know, just for the record.
FTSDR: