Another great, and frequently asked question!
Yucca, a tropical root vegetable, has a glycemic index of 55. As far as calorie content, a cup of yucca is similar to a cup of white potato, which we know is not part of the paleo diet.
For athletes, certain starchy tubers, like my favorite, the YAM, are the sole source of starchy carbs that we eat to prep for those long training hours on the bike and run.
If one uses yucca in their meals, and peels it (the skin is often the part of a plant that has a high anti nutrient content, such as saponins), cooks it and serves it along with green leafy veg, healthy lean proteins and some natural fat, a little bit now and then would be an acceptable part of a paleo entree.