First you say under ‘Yams’ that we all grew up eating them perpetuating the belief they are what we purchase in any grocery store. But then, in the chart, you correctly describe them as cylindrical with rough scaly skin which is NOT what we find at the store.

What we purchase as either Yams or Sweet Potatoes are in fact sweet potatoes. Both of them, regardless of the color. True Yams are brown, rough and scaly skinned resembling tree bark with white flesh and you would have to go on a dedicated search to find a specialty store that sells them.

Here in the U.S. ‘Yam’ and ‘Sweet Potato’ have just come to mean one is paler, starchy and not really sweet (more potato-like) while the other is darker orange, very soft after cooked and sweeter.

Unfortunately there doesn’t seem to be a rule on which is called which because I’ve seen them both labeled as ‘yams’ at different times. The safest thing to do is choose by color.