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CREOSOTE BUSH
CREOSOTE BUSH (Larrea tridentata)

This is one of the most common and characteristic desert plants, occurring as almost pure stands over large areas of land in the hot deserts of North America.


Extensive area of creosote bush experiencing extreme drought


Close-up of one of these plants, showing that most of the leaves have died. Note the presence of many holes made by burrowing animals (kangaroo rats and other rodents) in the soil round the base of the plant. Most of the desert animals shelter in these underground burrows during the heat of the day and emerge to forage at night.


Creosote bush in a period of abundant water availability - note the many small, resin-coated leaves and the many flowers or flower buds.


Close-up of leaves and flowers (with five bright-yellow sepals (not petals), twisted like the blades of a fan).

Details

Distribution: widespread in hot deserts, often in almost pure stands over several hectares.
Plant size: typically up to 1 metre, the plants being evenly spaced (probably due to competition for water, but possibly because the roots exude allelochemicals which inhibit the growth of other plants). Individual plants can live for up to 200 years, producing new stems from below soil level.
Leaves: small, consisting of two leaflets, joined at the base (like the foot of a deer). They have a thick, glossy cuticle to withstand water loss. They persist throughout the dry periods, but turn brown and eventually die in prolonged droughts. They contain resins, and smell like creosote when crushed.
Flowers: five bright-yellow sepals (not petals), twisted like the blades of a fan
Fruit: small, globose and covered in hairs.

The creosote bush thrives on well-drained areas of flat or sloping land - often with an underlying compacted soil layer of calcium (called caliche). Beneath the gravelly surface the soil consists of tightly packed sand and silt particles, with very little organic matter. These soils do not retain much water. pH is alkaline (inhibitory to most plants) and the annual rainfall is less than 25 cm. Almost all this rain falls as short, intense showers. The surface soil quickly becomes saturated by rain, and the packed soil particles prevent rapid water penetration, so much of the water runs off of the surface in flash floods. As a consequence, the only permanent plants (such as creosote bush) are those with extensive and deep root systems and with special adaptations to survive long periods of intense heat and drought.

The leaves of creosote bush contain anti-herbivory resinous compounds, so the plant is seldom eaten by grazing animals.

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