A tree, according to the University of Minnesota Extension, is a woody plant that grows from one central trunk to a height of at least 15 feet high. Shrubs, by contrast, may produce several trunks and generally remain under 15 feet high. Trees are divided into two main groups and then classified according to leaf shape and growth.
Deciduous or Coniferous
The first step in identifying tree leaves is to determine if the tree is deciduous or coniferous. Deciduous trees have broad-leaves that generally fall in the autumn. Coniferous trees produce overlapping, needle-like leaves that remain on the tree for several years.
Conifers generally produce needle-like leaves that may overlap. Some grow only 1 or 2 inches long, while others, such as the longleaf pine have needles as long as 24 inches. A few conifers, such as the bald cypress lose their leaves in the fall. Some, such as Eastern red cedar produce very short, overlapping scales.
The leaves of deciduous trees are categorized by shape. Untoothed, simple leaves are round or elongated ovals, and have smooth edges. These include the eastern redbud, flowering dogwood and laurel oak--among others. Toothed, simple leaves are also generally round or elongated ovals, with textured (or toothed) edges). Examples of toothed, simple leaved trees include American beech, black cherry, winged elm and red mulberry. Lobed, simple leaves are intricately shaped and may resemble stars or tulips. Common-lobed, simple-leaved trees include maples and oaks. Compound leaves are clusters of leaves formed on one stem. Trees with compound leaves include many nut trees, box elders and honey locusts.
To make matters more confusing, some broad-leaved trees don't lose their leaves, especially in mild climates. Southern magnolias and laurel trees remain green year-round. Privets and boxwood are shrubby trees that also share this characteristic.
Many trees, such as maples, aspens and elms are identified by brilliant fall foliage. Others, such as Paw Paw, produce unusual or unpleasant scents when the leaves are crushed. Some trees, such as the cherry laurel, produce toxic leaves. Buckeye, pecan, walnut, oak and hickory produce nuts, some of which are toxic to humans.