Listen up! In these United States anyway, whatever is signposted a "yam" in the supermarket, next to "sweet potatoes, " is also and actually a sweet potato. Yes. There are no "yams" distinct from sweet potatoes in Amurrica. The actual "yam" is a tropical African root veggie, with far less food value than the sumptuous sweet, and not at all related botanically to the sweet potato. They may be grown in Hawaii, but they rarely turn up on Thanksgiving tables. Oh, BTW, the Japanese love the sweet potato, a native of the Americas, which they enjoy in a myriad of varieties, many of them not sweet.
We poor Amurricans have to settle for three varieties, all of them sweet, none of them YAMS.