Trees: botanical naming, ecosystem, pictures


A tree can be defined as a large perennial woody plant. Though there is no set definition of minimum size, it is generally at least 6m (20 ft) high at maturity, and with branches supported on a single main stem. Compared with most other forms of plants, trees are long-lived. A few species of trees grow to 100m tall, and some can live for several millennia.

Trees are often classified according to whether they drop their leaves (‘deciduous’) or do not (‘evergreen’).
Another way of grouping trees is by the way they reproduce: Angiosperms produce seed from within the flower, whereas Gymnosperms do not have flowers, but bear their seeds on cones.

Next trees are divided by family or genus, which is a group with broadly similar characteristics, appearance and technical features.
A species is the name for a group of similar individual trees in the same genus. Then a species can be subdivided into varieties, which are trees of the same species but with some specific difference, such as colour, which has occurred naturally. Varieties are often deliberately bred for some characteristic, in which case they would be called ‘cultivars’.

Like other plants, trees have common names and botanical Latin names. Here are some well-known examples with their botanical name in brackets:
Oak (quercus genus)
Ash (fraxinus genus)
Spruce (picea genus)
Elm (ulmus genus)
Maple (acer genus)
California redwood (sequoia sempervirens)

You may have noticed that the genus is usually in italics. The cultivar, by convention, has single inverted commas round it. Agapanthus means lily (genus), so the naturally occurring African Lily is Agapanthus africanus (species), and the artificially bred white one (cultivar) is ‘Agapanthusis Africanus ‘Albus’.
The main advantage in using Latin is that the same genii and species can be labelled the same, regardless of the country they are found in. Another advantage is that since Latin is a ‘dead’ language, it is not still changing in the way that German or English is.

In scientific names the genus always comes first, then the species, then the sub-species if there is one, and lastly the variety. For example, Acers belong in a family called Sapindaceae (soap berries) which includes 135 genera and 1,600 species.
Acer genus (maple)
Acer campestre (field maple)
Acer platanoides (Norway maple)
Acer rubrum (red maple)

This Latin naming system (‘taxonomy’) which is used for all living things was invented by Carolus Linnaeus in 1753, and it has proved so useful that it has never been changed. A plant breeder or plant collector who has discovered a new plant may name it, but colleagues and botanists worldwide will have a say in it when it has been identified. The good thing is that local names for the same plant may differ, but once it has been given a Latin botanical name it is fixed, unless botanists discover something about the tree or plant that means it has been misnamed.

The earliest trees were tree ferns and horsetails, which grew in vast forests in the Carboniferous Period; tree ferns still survive, but the only surviving horsetails are not of tree form. Later, in the Triassic Period, conifers, ginkgos, cycads and other gymnosperms appeared, and subsequently flowering plants in the Cretaceous Period. Most species of trees today are flowering plants and conifers.
The benefits of trees
It is estimated that humans clear an area of forest on our planet equivalent to a football pitch every two seconds. But apart from the loss of the beauty of those trees (and the free pictures clearly show that beauty), why should we care?

Well for a start trees provide a habitat for insects, bird and other animals. Secondly trees absorb carbon dioxide and give out oxygen – just the opposite to humans – and are therefore directly beneficial to us: one large tree produces enough oxygen every day for four people. Then trees can reduce global warming by locking up carbon and other harmful gasses like sulphur dioxide: while we burn potentially harmful fossil fuels, trees work away absorbing the resulting carbon: an acre of trees can store 2.6 tons of carbon dioxide a year. (For European readers that’s 0.4 of a hectare of trees will absorb 2.3 tonnes.) Looked at another way, if you drive 10,000 miles at 30 miles per gallon, you need 10 trees to remove the CO2 you produce.

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