Yams and sweet potatoes might be different in your mind, and you probably have an idea of what yams are, but the reality is, if you're an American, you've probably never had a true yam. You might not even know anyone who has. Nevertheless, they exist and are important.
In America, grocery stores tend to call sweet potatoes yams if they get soft when cooked. Otherwise, they call them sweet potatoes. But, soft, firm, orange, yellow, or dark orange, they're all sweet potatoes (usually).
If you're eating traditional yams at Thanksgiving, those are sweet potatoes.
When you read about scientific studies on yams, and hormonal properties of them, then they're probably talking about Dioscorea.
Location: SW Idaho, USA
USDA hardiness zone: 6
Elevation: 2,260 feet Profile post