Clementines are a delicious plant so they can absolutely be incorporated into a Paleo diet. These little citruses are packed with vitamin C, calcium, magnesium, and potassium. They are also very sweet, containing a whopping 12.02 grams of carbohydrates per 100 grams of fruit and only 1.7 grams of fiber. The result can mean a significant rise in blood sugar after consumption.
Paleo and Blood Sugar
Elevated blood sugar tends to lead to a crash later, leaving feelings of fatigue and lethargy. A rise in blood sugar also means a rise in insulin, which is not necessarily a bad thing if done once in awhile, but chronically high insulin levels lead to inflammation and insulin resistance, neither of which is desirable. Occasional consumption of clementines (particularly seasonal) should be fine, but they should not be eaten every day.
Some people can handle a serving of fruit or two every day. Others need to severely restrict their carbohydrate intake. If you know that you are particularly sensitive to sugar, then staying away from clementines is probably advisable. The only way to know for sure is to experiment and see what works best for you.
Mark Sisson has a whole post on the various sugars available to us (including the type of sugar found in fruit) on his blog.