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A tree can be defined as a large woody perennial plant. Though there is no set definition of size, it is generally at least 4.5 m (15 ft) high at maturity, and with branches supported on a single main stem. Trees are important components of the natural landscape and significant elements in landscaping. Compared with most other forms of plants, trees are long-lived. A few species of trees grow to over 100 m (300 ft) tall and some live for several millennia.