Some examples of tree nuts include walnuts, pecans, macadamia nuts and hazelnuts. These are botanical nuts, which means that they're fruits made of a seed enclosed in a hard shell. The shell needs to be cracked to release them.
The walnut tree is grown for its timber as well as its fruit. However, the tree releases a toxin called juglone that kills or stunts many types of plants that might grow next to it. The walnut itself is very rich in omega-3 fatty acids, which help balance cholesterol levels. Walnuts are also a good source of copper, manganese and biotin. The papery skin over the nut is high in beneficial phenols.
The pecan tree is a member of the hickory family, and pecans have more fat than almost any other nut. Available in a variety of sizes, the pecan is prized for its role in pralines and pecan pies.
The macadamia is a round, buttery nut that's grown in warm climates. Like the pecan, it's fairly high in fat but is a good source of vitamin B, iron, magnesium and phosphorus.
Also known as filberts, hazelnuts can be eaten raw or cooked and are found in instant coffees, chocolate, ice cream and other confections. They're a good source of protein, the B-complex vitamins and vitamin E.