A leaf is one of the expanded, usually green organs borne by the stem of a plant.
Leaves are the most important organs of most vascular plants.
They are usually borne above ground and specialized for photosynthesis.
Leaves manufacture food for plants, which in turn ultimately nourish and sustain all land animals.
They are mostly green in color. This is due to the presence of a compound called chlorophyll. This compound is essential for photosynthesis as it absorbs light energy from the sun.
Certain organs that are superficially very different from the usual green leaf are formed in the same manner and are actually modified leaves – among these are the sharp spines of cacti, the needles of pines and other conifers, and the scales of an asparagus stalk or a lily bulb.
Leaves vary tremendously in shape and in size: from the tiny leaves (less than 1 millimeter across) of the floating aquatic plant duckweed to the giant leaves (25 m (82 ft) long and 3 m (9.8 ft) wide) of the raffia palm.
Plant species are often recognized by their distinctive leaf shapes.
Some species, however, are distinguished by producing more than one leaf shape on the same plant, a phenomenon known as heterophylly.
During the autumn, deciduous trees change color and then lose their leaves. This is in preparation for the winter season. Because it gets so cold, the trees have adapted to the winter by going into a period of dormancy or sleep.
Leaves are collectively referred to as foliage, as in “autumn foliage”.
Clovers feature alternate compound leaves, usually with three toothed leaflets. Clovers occasionally have four leaflets, instead of the usual three. These four-leaf clovers, like other rarities, are
considered lucky.
It is claimed that there are approximately 10,000 three-leaf clovers for every four-leaf clover. However, an actual survey of over 5 million clovers found the real frequency to be closer to 5,000 to 1, twice the said probability.
Clovers can also have five, six, or more leaflets, but these are rarer still. The record for most leaflets is 56, set on 10 May 2009. This beat the “21-leaf clover”, a record set in June 2008 by the same discoverer, who had also held the prior Guinness World Record of 18.
Leaves of some vegetables is widely use as a salad.
Lettuce is without doubt the world’s most popular salad plant.
Some leaves are used for seasoning and flavoring food.
Tea is an aromatic beverage commonly prepared by pouring hot or boiling water over cured leaves of the Camellia sinensis, an evergreen shrub (bush) native to East Asia. After water, it is the most widely consumed drink in the world.
Animals and insects that eat mostly leaves — such as pandas, caterpillars, giraffes or koalas — are called folivores.
Koalas, Greater Gliders and Ringtail Possums, are only mammals which can survive on a diet of eucalyptus leaves. Eucalyptus leaves are very fibrous and low in nutrition, and to most animals are extremely poisonous.
The longest-lived leaves of all plants belong to the welwitschia, named after botanist, Dr Friedrich Welwitsch (Austria), who discovered the plant (looking like a “stranded octopus”) in 1859 in its native Namib Desert of Namibia and Angola. The welwitschia has an estimated lifespan of between 400 and 1,500 years, with some specimens carbon-dated to 2,000 years old. Each plant produces two leaves per century, and never sheds them. Ancient individuals sprawl out over 10 m (33 ft) in circumference, with enough foliage to cover a 400-m (1,312-ft) athletic field.