Tree

A tree is defined as a perennial plant consisting of one or more large woody
stems. The component parts of a tree are the roots, trunk(s), branches,
twigs and leaves. A small group of trees growing together is called a grove
or coppice, and a large population of mixed tree species is called a forest.

Tree stems consist mainly of transport tissues (xylem and phloem). In fact,
wood consists of xylem cells, and the bark is primarily made of phloem. As
the tree grows it creates annual grow rings, which can be counted to
determine the age of the tree, and used to date timber that has been cut
from trees in the past using the science of dendrochronology.

The roots of a tree are generally embedded in earth and absorb water and
nutrients from the surrounding soil. Above ground, the trunk gives height to
the leaf-bearing branches to aid in their competition with other trees for
sunlight. In many tree species, the branches spread so as to present the
largest possible leaf surface area to the sun.

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

Some types of tree can grow to over 100 meters tall and/or live for several
millennia if circumstances are optimal. A plant that is similar to trees,
but generally having smaller, multiple trunks, is often called a shrub,
although boundary between the two categories is not precise.

Several biotopes are defined largely by the trees that inhabit them, for
example, the rainforest and the taiga.

Trees often serve as important symbols in mythologies and religions.
Examples are Yggdrasil in the Norse Mythology, the Christmas Tree that is
derived from Germanic mythology, the Tree of Knowledge of Judaism and
Christianity, and the Bodhi tree in Buddhism.

Trees show a wide variety of leaf types and shapes, bark, flowers, fruit,
etc. Trees occur in several diverse families of plants. The earliest trees
were probably tree ferns, which once grew in vast forests. Later the
conifers, ginkgos and cycads appeared (modern cycads no longer appear as
trees). Most species of trees today are flowering plants, which were the
most recent to appear. The list below gives some examples of well known
trees and how they are typically classified.

Flowering plants (Magnoliophyta)

   * Aceraceae family
        o Norway Maple, Acer platanoides
        o European Sycamore, Acer pseudoplatanus
        o Red Maple, Acer rubrum
   * Aquifoliaceae family
        o Common Holly, Ilex aquifolium
        o Tarajo Holly, Ilex latifolia
   * Betulaceae family
        o Common Alder, Alnus glutinosa
        o Silver Birch, Betula pendula
   * Fagaceae family
        o Sweet Chestnut, Castanea sativa
        o American Beech, Fagus grandifolia
        o Oriental Beech, Fagus orientalis
        o Common Beech, Fagus sylvatica
        o Black Beech, Nothofagus solandri
        o English Oak, Quercus robur
   * Fouquieriaceae family
        o Boojum, Fouquieria columnaris
   * Juglandaceae family
        o Common Walnut, Juglans Regia
        o Black Walnut, Juglans nigra
        o Hickories, Carya species
   * Leguminosae family
        o Honey Locust (Gleditsia triacanthos)
        o Pau Brasil, Brazilwood, South American Redwood, Caesalpinia
          echinata
        o Sappanwood, East Indian Redwood, Caesalpinia sappan
   * Meliaceae family (Mahogany family)
        o Neem, Azadirachta indica (A. Juss)
        o Thai Neem, Azadirachta siamensis
        o Marango, Azadirachta excelsa (Jack)
        o Persian Lilac, Melia azedarach
        o Melia toosendan
        o Gurke, Melia volkensii
        o Mahogany, Swietenia mahagoni
   * Myristicaceae family
        o Nutmeg, Mysristica fragrans
   * Myrtaceae family
        o Silver Gum, Eucalyptus cordata
   * Oleaceae family
        o Olive, Olea europaea
   * Palmae family, also called Palmaceae or Arecaceae, the palm family
        o Areca Nut, sometimes miscalled "Betel Nut", Areca catechu
        o Coconut Cocos nucifera
        o Canary Island Date Palm, Phoenix canariensis
        o date Palm, Phoenix dactylifera
        o Chusan Palm, Trachycarpus fortunei
   * Rhizophoraceae, the mangrove family
        o Red Mangrove, Rhizophora mangle
   * Rosaceae family
        o Common Hawthorn, Crataegus monogyna
        o apple, Malus domestica
        o Apricot, Prunus armeniaca
        o Almond, Prunus dulcis
        o Fuji Cherry, Prunus incisa
        o Peach, Prunus persica
        o Pear, Pyrus communis
        o Rowan, Sorbus aucuparia
   * Rubiaceae family
        o coffee, Coffea arabica
        o coffee, Coffea robusta
   * Rutaceae family
        o Lime, Citrus aurantiifolia
        o Sour Orange, Citrus aurantium, Citrus bigaradia, Citrus vulgaris
        o Sweet Orange, Citrus sinensis
        o Grapefruit, Citrus paradisi
        o Mandarin, also called Tangerine, Citrus reticulata, Citrus nobilis
        o Lemon, Citrus limon, Citrus limonum
        o Satsuma, Citrus unshiu, Citrus reticulata, Citrus nobilis
   * Salicaceae family
        o Aspen, Populus tremula
   * Sapotaceae family
        o Tambalacoque, or dodo tree, Sideroxylon grandiflorum, previously
          Calvaria major
   * Sterculiaceae family
        o Cacao, the source of cocoa, Theobroma cacao
   * Tiliaceae family. The Lime trees in this family are also known as
     Linden trees: see Tilia.
        o American Lime, Tilia americana
        o Common Lime, Tilia europaea
        o Mongolian Lime, Tilia mongolica
        o Silver Lime, Tilia tomentosa, Tilia argentea

Conifers

   * Cupressaceae family
        o Alerce or Patagonian cypress, Fitzroya cupressoides
        o Eastern redcedar, Juniperus virginiana
   * Pinaceae family
        o Norway spruce, Picea abies
        o European larch, Larix decidua
        o Stone pine, Pinus pinea
        o Monterey pine, Pinus Radiata
        o White pine, Pinus strobus
        o Scots Pine, Pinus sylvestris
        o Douglas-fir, Pseudotsuga menziesii
        o Bigcone Douglas-fir, Pseudotsuga macrocarpa
   * Taxodiaceae family
        o Japanese Cedar, Cryptomeria japonica
        o California Coast redwood, Sequoia sempervirens
        o Giant sequoia or Giant redwood, Sequoiadendron giganteum
        o Chinese Dawn redwood, Metasequoia glyptostroboides
        o Baldcypress, Taxodium distichum, Taxodium ascendens, Taxodium
          mucronatum

Ginkgos

   * Ginkgoaceae family
        o Ginkgo, Ginkgo biloba

Ferns

   * Cyatheaceae and Dicksoniaceae families
        o Tree ferns, Cyathea, Alsophila, Dicksonia

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