Well, I'm looking at a different chart and it says differently. Also, where you get them from matters a lot.
For example, Australian sweet potatoes had a GI of 44, which is fairly low, but New Zealand sweet potatoes had a GI of about 78, which is quite high. The average given for all the sweet potatoes is 66, which falls under the "moderate" category, but I consider that to be fiarly high.
However, "yams" from New Zealand ranged from 25-35, which is pretty darn low.
BUT, the thing I'm now confused about is what they are calling a yam. Is a "yam" a dark orange moist sweet potato?