Linden trees are attractive trees that are ideal for urban landscapes because they tolerate a wide range of adverse conditions, including pollution. One problem with these trees is that they attract insects. Aphids leave sticky sap on the leaves and cottony scale insects look like fuzzy growths on the twigs and stems. It's hard to control these insects on a tall tree, but the damage is temporary and the tree gets a fresh start each spring. Here are the linden tree varieties most often seen in North American landscapes: