Thursday, October 30, 2008


These are the plants of the deserts or other dry places. For this reason they must have some method of withstanding long periods of drought, very bright light, strong winds and, perhaps, very high temperatures – although not all deserts are hot.

There are various ways in which plants can overcome these conditions. With annual plants, the seeds often have a long life and will only germinate after rainfall. They then grow very rapidly and complete their life cycle before the drought occurs. On the other hand perennial plants have to exist through bad spells and usually have some method of storing up moisture to tide them over. Cacti are a good example of this with their swollen fleshy growth.

Large thin flat leaves would be of no use in the desert as they would evaporate too much moisture from their surfaces, so leaves are often very small or narrow, and usually have very thick outer layer (cuticle), preventing water loss. They might even be reduced in size to hard spines as in many cacti and succulents. The Yucca has leaves which are narrow and with a very tough cuticle to withstand the desert conditions in America.

Roots may be adapted to store water, becoming thick and fleshy, and it is noticeable that in drier parts of the world, such as the Middle East, there are many plants which produce underground bulbs, corms or tubers. Leaves can also be thick and fleshy for water storage, or develop only during the rainy season, to drop off again when the dry summer comes.

Some grasses can roll their leaves inwards from the edges in dry spells, thus leaving a smaller surface exposed to the sun, while acacias in Australia can turn their leaves sideways on to the sun so that it does not scorch down on to the flat surfaces. Leaves sometimes have dense coverings of hairs to protect them from sun and drying winds.

Plants which grow in places where the soil is very salty, such as by the sea, in river mouths or salt lakes inland, and have adapted themselves to overcome the peculiar conditions, are called halophytes. Most normal land plants are killed by salt in the soil but these plants are so successful that they can be important to man when trying to reclaim new land from the sea.

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