To anyone who cooks...?

Although yams and sweet potatoes are both angiosperms (flowering plants), they are not related botanically. Yams are a monocot (a plant having one embryonic seed leaf) and from the Dioscoreaceae or Yam family. Sweet Potatoes, often called ‘yams’, are a dicot (a plant having two embryonic seed leaves) and are from the Convolvulacea or morning glory family

Popular in the American South, these yellow or orange tubers are elongated with ends that taper to a point and are of two dominant types. The paler-skinned sweet potato has a thin, light yellow skin with pale yellow flesh which is not sweet and has a dry, crumbly texture similar to a white baking potato. The darker-skinned variety (which is most often called "yam" in error) has a thicker, dark orange to reddish skin with a vivid orange, sweet flesh and a moist texture.

These website will explain in full detail for you the differences between the two.