4. Norway maple (Acer platanoides)
Norway maples are often confused with sugar maples, which are native to North America. The Norway maple grows quickly, often reaching heights of 60 to 90 feet. Introduced from Europe in the mid 1700s for cultivation as an ornamental tree, it can be distinguished from other maple trees because the leaves and twigs ooze milky sap when cut. In the garden, Norway maples are often attacked by black spot fungus leaving mildew-like white splotches on the leaves. In native forest, these trees can grow in deep shade and often choke out any hope of tree seedlings ever reaching maturity. Norway maples also prevent anything from growing under their leaf canopy because they are so efficient in absorbing available water and nutrients.