A tree can be defined as a large, perennial, woody plant.
Though there is no set definition regarding minimum size, the term generally applies to plants at least 6 m (20 ft) high at maturity and, more important, having secondary branches supported on a single main stem or trunk with clear apical dominance.
Compared with most other plant forms, trees are long-lived.
A few species of trees grow to 100 m (328 ft) tall and some can live for several thousand years. Trees are important components of the natural landscape due to their prevention of erosion and significant elements in landscaping and agriculture, both for their aesthetic appeal and their orchard crops (such as apples).
Wood from trees is a common building material.
The basic parts of a tree are the roots, trunk(s), branches, twigs and leaves.
Tree stems consist mainly of support and transport tissues (xylem and phloem).
Trees may be broadly grouped into exogenous and endogenous trees according to the way in which their stem diameter increases.
Exogenous trees, which comprise the great majority of modern trees (all conifers, and all broadleaf trees), grow by the addition of new wood outwards, immediately under the bark.
Endogenous trees, mainly in the monocotyledons (e.g.
palms), grow by addition of new material inwards. As an exogenous tree grows, it creates growth rings.
In temperate climates, these are commonly visible due to changes in the rate of growth with temperature variation over an annual cycle.
These rings can be counted to determine the age of the tree, and used to date cores or even wood taken from trees in the past; this practice is known as the science of dendrochronology.
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