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One doesn't have to look far to see a wonder of the plant world in Joshua
Tree National Park. Known scientifically as Larrea tridentata, and
in common parlance as the creosote bush, it produces small, pretty yellow
flowers in spring and summer. But it is the pleasantly pungent smell, which
the leaves produce as soon as a summer rain starts, that is most noticeable. |
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| The creosote bush is the signature plant of the southern part
of the park and a common, characteristic, and often dominant shrub of the
deserts of southwestern North America. Its closest relative lives in the
arid regions of Argentina. |
| Actually, what botanists classify as a single species in the
North American deserts is now known to consist of three genetically different
shrubs. Creosote bushes of the Mojave Desert have 78 chromosomes, those
of the Sonoran Desert (southern Arizona) have 52 chromosomes, while those
of west Texas (Chihuahuan Desert) have only 26. Such an increase in the
number of chromosomes in plant evolution is not that unusual. Seedless watermelons,
for example, were the result of doubling the number of chromosomes of regular
watermelons, the lack of seeds being a side effect. In the case of the Mojave
creosote, the increase in chromosome number may have been accompanied by
an increasing ability to survive on the less summer rainfall in the Mojave. |
| The genetic and fossil evidence indicate that the Mojave creosote
is a relative newcomer to our part of California. Eleven to 12,000 years
ago, at the end of the Ice Age, this area would have been dominated by juniper
woodland and lots of grass. As the climate became warmer and drier the junipers
retreated to the nearby mountains, and a new plant, evolved from the Sonoran
Desert form, appeared on the scene: our creosote bush. The newcomer was
so successful in the competition for scarce water that it soon became the
largest and most conspicuous plant of our desert landscape. |
| Although creosote bushes produce large numbers of fuzzy seeds
at each flowering, few of them are able to germinate. It takes decades for
creosote bushes to return to areas that have been cleared of native shrubs.
Even a one-foot high plant is probably at least ten years old. As the shrub
grows, branches continue to originate around the periphery of the original
stem crown. The branches grow upward for about six feet giving the whole
shrub the rounded shape of an upside down cone. |
| As growth continues, the oldest branches gradually die and
the stem crown splits into separate crowns. This happens at an age of 30
to 90 years. Eventually, the original stem and early branches die and rot
away; the connections between adjoining segments of the stem crown thus
disappear. The plant has now become a clone, composed of several independent
stem crowns all descended from one seedling. The process continues until
the clone spreads across the ground in a circular or elliptical shape. As
you travel in the park, see if you can find one or more of these circular
creosote clones. Usually, a mound of sand accumulates in the central area. |
| In a few areas of the Mojave Desert clonal creosote rings
have been found that are several yards in diameter. Near Lucerne Valley,
"King Clone" has an average diameter of 45 feet! Using radiocarbon
dating and known growth rates of creosote, scientists have estimated the
age of "King Clone" as 11,700 years. Some of these common residents
have been here continuously since the last ice age. They are certainly an
integral part of our desert environment and many desert animals depend on
the creosote for food and shelter. |
| The Indians of the Southwest appreciated the creosote bush.
The leaves were an important part of their pharmacopoeia. The Apaches
prescribed
chewing and swallowing a small piece of creosote branch to cure diarrhea.
Other tribes made a strong tea from the dried leaves to treat the common
cold. The resinous leaf nodes were used to soothe bruises and wounds. And
a tea made from the leaves and sweetened with a little honey was said
to
greatly relieve kidney pain. |
| Modern herbalists also have found uses for the ancient creosote.
An extract is now marketed as a cure for herpes. Another extract is being
investigated as an anti-cancer drug. However, large doses of creosote have
been shown to cause liver damage. |
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http://www.nps.gov/jotr/nature/plants/shrubs/creosote.html
last modified: 11/06/02
web editor: Sandra kaye |
