Trees range in size from thin palms to strong oaks and from stout beeches to tall redwoods. Despite this wide range in dimension and appearance, almost all trees start out as a tiny seed. These seeds are protected, nourished and dispersed by different mechanisms, including fruit, cones, leaves and even round seed pods.
The walnut tree is a broad-leafed tree that originated to the north of Persia. The tree grows quickly, reaching up to 20 feet in the first 10 years, when it begins to produce its first batch of round seed pods that come in husks and begin smooth but then crumple into a hard exterior and drop to the ground. These break open to reveal a nut and seed that have become a popular snack in many cultures. The walnut tree can reach up to 70 feet with a 5-foot trunk diameter or greater and a crown of broad five- to seven-pointed green leaves. Walnut is often used in the manufacture of furniture and musical instruments such as pianos.
The plane tree is one of a select group of broad-leafed trees that produce catkins, small flowers that have no petals, and which also later produce smooth and round seed pods used to protect and concentrate seeds. The plane tree is an ancient tree that can reach up to 100 feet tall, with a cylindrical stem and broad-lobe pointed leaves on long stalks that can reach out 9 inches or more. Plane trees are characterised by bark that flakes off and falls in large rectangular pieces. Although the plane tree has a fine-grain wood, it is somewhat brittle and used more for ornamental purposes than furniture. Plane trees grow in Asia, Europe and the United States, although United States plane trees do not reach the towering heights of their Asian cousins.
Unlike the plane tree and the walnut, the hop tree produces flat, round seed pods. A native of Canada and the eastern United States, this tree grows an average of 1 foot per year and grows up to 25 feet tall. The leaves of this tree are dark green and oval-shaped, turning brown, red and yellow during the winter. This plant produces round, flat disclike seed pods that glide on the air to new patches of soil to propagate. This tree is sometimes used as firewood but is more often kept in nurseries to be planted in yards for aesthetic value.