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A tree is a plant consisting of roots, one or more large stems called trunks, branches, twigs and leaves. In analogy with skin, a tree has bark to protect it against infections and fungus attacks, and also to transport nutrients and water to the growth zones along the branches and leaves. A small group of trees growing together is called a grove whereas a large population of trees is called a forest.

In mathematics, a tree is a kind of graph.

In computer science, a tree is a kind of hyerarchical data structure.

The rest of this article develops the original meaning of tree in botany.

The roots of a tree stand embedded in earth and extract water and nutrients from the surrounding soil. Above ground, the trunk gives height to the leaf-bearing branches in order to compete for sunlight. In many species of tree, the branches spread to present the largest possible leaf surface to the sun.

A tree may not have all of the organs mentioned here: most palms do not have branches, the saguaro of North America has no functional leaves, and tree ferns don't have bark. Based on their rough shape and size, all these are considered trees nonetheless.

Some types of tree can grow to over 100 meters of height and/or live for several millennia if circumstances are optimal. A smaller variant of tree, generally with smaller, or multiple trunks, is often called a shrub, though there's no precise boundary between the two categories.

Several biotopes are defined largely by the trees that inhabit them: The rainforest and the taiga are examples.

Trees often serve as important symbols in mythologies and religions. Examples are Yggdrasil in the Norse Mythology and the Tree of Knowledge of christianity.

Trees show a wide variety of leaf types and shapes, bark, flowers, fruit, etc. Types of tree include:

• Broadleaves
  • Aceraceae family
    • Norway Maple, Acer platanoides
    • Sycamore, Acer pseudoplatanus
    • Red Maple, Acer rubrum
  • Aquifoliaceae family
    • Common Holly, Ilex aquifolium
    • Tarajo Holly, Ilex latifolia
  • Betulaceae family
    • Common Alder, Alnus glutinosa
    • Silver Birch, Betula pendula
  • Fagaceae family
    • Sweet Chestnut, Castanea sativa
    • American Beech, Fagus grandifolia
    • Oriental Beech, Fagus orientalis
    • Common Beech, Fagus sylvatica
    • Black Beech, Nothofagus solandri
    • English Oak, Quercus robur
  • Leguminosae family
    • Pau Brasil, Brazilwood, South American Redwood, Caesalpinia echinata
    • Sappanwood, East Indian Redwood, Caesalpinia sappan
  • Meliaceae family (Mahogany family)
    • Neem, Azadirachta indica (A. Juss)
    • Thai Neem, Azadirachta siamensis
    • Marango, Azadirachta excelsa (Jack)
    • Persian Lilac, Melia azedarach
    • Melia toosendan
    • Gurke, Melia volkensii
    • Mahogany, Swietenia mahagoni
  • Myrtaceae family
    • Silver Gum, Eucalyptus cordata
  • Palmae family, also called Palmaceae, the palm family
    • Areca Nut, sometimes miscalled "Betel Nut", Areca catechu
    • Chusan Palm, Trachycarpus fortunei
  • Rosaceae family
    • Common Hawthorn, Crataegus monogyna
    • Apple, Malus domestica
    • Apricot, Prunus armeniaca
    • Almond, Prunus dulcis
    • Fuji Cherry, Prunus incisa
    • Peach, Prunus persica
    • Pear, Pyrus communis
    • Rowan, Sorbus aucuparia
  • Salicaceae family
    • Aspen, Populus tremula

• Conifers
  • Cupressaceae family
    • Alerce aka Patagonian Cypress, Fitzroya cupressoides
  • Pinaceae family
    • Norway Spruce, Picea abies
    • European Larch, Larix decidua
    • Stone Pine, Pinus pinea
    • Monterey Pine, Pinus Radiata
    • Douglas Fir, Pseudotsuga menziesii
  • Taxodiaceae family
    • Japanese Cedar, Cryptomeria japonica
    • California Coast Redwood, Sequoia sempervirens
    • Giant Californa Redwood, Sequoiadendron giganteum
    • Chinese Dawn Redwood, Metasequoia glyptostroboides
• Others, unclassified

• Ebenholtz
• Mangrove
• Dodo tree, or tambalacoque, Calvaria major