The most common plant in the Northern Chihuahuan Desert is, by far, the Creosote bush. It thrives in nearly every habitat the desert has to offer, and in many areas is one of only two or three species to be found. In severely damaged habitats it is sometimes the only plant able to grow. Creosote and an unrelated plant, tarbush, are defining plants of the Chihuahuan Desert.
Creosote is so common in its range it goes largely unnoticed, even by naturalists. Yet this plant is extraordinary by almost any standard one might care to apply. Creosote is the most drought-tolerant plant in North America. It can live with no rain at all for more than two years and survives even prolonged droughts handily. In fact, Creosote fares poorly in years when rainfall is abundant. In the Big Bend area, for example, Creosote did very well during the drought of 1960 to 1967; when the rains returned in late 1967, Creosote’s range began to shrink, and continued to shrink until 1981 when rainfall amounts dropped to normal.
Desert plants have evolved a number of strategies for survival in the desert. Creosote is remarkable in the range of adaptations it has evolved and the number it employs. It is this combination of adaptations that allows Creosote to live where practically nothing else can. There are areas north of the Chisos Mountains where the only plant living is the Creosote bush.
Many desert plants use tap roots to reach moisture that lies deep beneath the surface and that doesn’t run off or evaporate readily. Others use thin, fibrous roots that grow just beneath the surface to capture rainwater quickly. Creosote uses both; it can catch water from brief rains and from deep underground resources as well. Its taproot can reach depths of 10 feet; it is so tough it can penetrate caliche, something that few plants can do. The shallow root system penetrates only a few inches into the soil but may spread out to cover as much as 50 square yards. These roots hydrate quickly and are capable of using even brief rains.
Like cacti, Creosote stores water, minerals, and vital nutrients for dry spells. Retaining moisture and nutrients in its crown allows Creosote to bloom whether it rains or not. So Creosote blooms both seasonally (in the spring) and opportunistically after any rain of more than an inch. Quick to capture water, and quick to bloom, Creosote is nevertheless careful with its blossoms. Since there is no value in attracting pollinating insects after a blossom is fertilized, the petals of a fertilized blossom rotate a quarter turn thus making them less conspicuous. Insects then visit unfertilized blossoms preferentially. Because Creosote blooms both seasonally and opportunistically, it is not unusual to see plants during the late-summer monsoons putting out new shoots, blooming, and setting seed at the same time. The following photograph shows this condition. Here you can see an unfertilized blossom (top blossom), a fertilized blossom (below) lush green sticky leaves and ripening seed pods all on the same stem.
Oddly, Creosote uses the “C3” photosynthesis process which is not very productive during much of the day. Creosote compensates for this by positioning its leaves so that they get the most sun early while it is still cool. Supporting stems grow in the shape of a flat fan which serves to orient the leaves in the correct direction.
Creosote plants adjust their shape to fit the microhabitat in which they live. In the driest climates, limbs grow straight and at a funneling angle that allows the leaves to collect rain and channel it to the plant’s crown. In wetter areas, the plant assumes a rounder shape, casting a broader shade and keeping surface root temperatures lower.
For further protection Creosote coats its leaves with resins and other chemicals that retard evaporation and give the plant such a nasty taste that few animals will eat it. Resin content of the leaves may be over 25% by weight in young leaves, dropping to around 11% when the leaf gets old. The most desirable leaves (the tender young ones) are the worst tasting. Kangaroo rats, starving wood rats, and desperately thirsty jack rabbits that do venture to eat Creosote prefer to eat the older leaves that are less efficient at photosynthesis.
Like many leafy desert plants, Creosote sheds leaves during particularly dry spells, and like others it withdraws important nutrients from the leaves before shedding them. But Creosote is exceptionally efficient at this process reabsorbing three-fourths of its phosphorus and over half of its nitrogen before dropping a leaf. The fallen leaves accumulate under the shrub along with other wind-blown detritus and creates an ecological microcommunity that is specific to the Creosote bush canopy, sheltering and feeding beetles, millipedes, pocket mice, and kangaroo rats.
Creosote and most dryland grasses simply don’t get along well. In the presence of Black Gramma for example, Creosote seeds will not germinate. Conversely, wherever Creosote lives, most grasses are conspicuously absent. Ironically, this aversion to grass has served Creosote well in recent times, for wherever ranges are overgrazed, Creosote habitat is created, a situation the shrub is quick to exploit. Once established, Creosote is practically impossible to remove, so to lose a range to Creosote is to lose it forever.
Perhaps the most remarkable adaptation of Creosote is its’ longevity. It clones itself starting from the crown, often growing in rings like a donut. These rings grow extraordinarily slowly; a 20 foot ring may be 3,000 years old or more. Using radiocarbon dating, one shrub in the Mojave desert has been assayed at 11,700 years of age and one shrub in the Sonoran desert near Yuma, Arizona is thought to be 18,000 years old. If you consider rings of clones to be part of the same plant, these creosote bushes are the oldest living things on earth!
Long before the Spaniards arrived, native Americans used Creosote for a wide range of ailments. Now modern laboratories are confirming what the Indians had learned from experience. Today, creosote is known to possess analgesic, antiseptic, antiviral, and antibiotic properties.
Creosote contains a mixture of resins and “phenols.” Phenols are compounds that occur widely in foods and tend to be quite chemically active. Phenols are responsible for the bite in chili peppers, the sting in clove oil, and the smokey flavor in coffee and whiskey. Some are powerful antioxidants and antiseptics. Creosote also produces 18 distinct flavones, chemicals found in grains that are known to have beneficial effects against atherosclerosis, osteoporosis, diabetes mellitus, and certain cancers.
Possibly the most important chemical creosote produces is a compound known as NDGA. NDGA is a potent antioxidant. It is believed to suppress the formation of free radicals in bodily cells and thereby promote longevity. It was widely used as a food preservative until the 1950s. NDGA has been shown in the lab to suppress HIV replication in infected human cells and to disturb the metabolism of some cancers.
The Tohono O’odham Nation considered Creosote a sacred plant. In their cosmology, Earth Maker took soil from his breast, scattered it about, and the first plant to grow was Creosote. Creosote was the most important plant in Tohono O’odham pharmacology and is still used throughout the Southwest.
Creosote was often taken internally for gastrointestinal problems. People chewed and swallowed the gum to control dysentery and intestinal spasms. They drank infusions for bowel complaints and old men drank Creosote tea to improve the flow of urine. In cases of suspected poisoning infusions could also be used to induce vomiting.
Creosote was widely used in treating respiratory problems. It’s decongestant properties were relived symptoms of colds, asthma, and respiratory infections. Decoctions of the gum were often taken for colds. Horses with colds, distemper, or runny noses often found creosote in their feed.
Infusions, or teas, were made by soaking the Creosote plant and used to treat bowel complaints. Old men used them as a diuretic, and healers administered them in cases of suspected food poisoning to make the patient vomit. Parents washed children’s impetigo sores with infusions while others used them as disinfectants, deodorizers, and a treatment for dandruff. One tribe even used infusions to treat cancer, an interesting application, because extracts of Creosote have recently been found to kill some types of cancer cells in the lab and even to inhibit the growth of HIV. Creosote is too toxic to be useful in cancer and HIV therapy yet, but further study may reveal new compounds for the treatment of these diseases.
Creosote’s anti-inflammatory properties made it useful in poultices, infusions, and decoctions applied directly to aching joints to relieve the pain of rheumatism, arthritis, sprains and bruises.
Natives used decoctions of leaves, stems, and gum as an antiseptic – they gargled it for sore throats, prepared decoctions for collar sores on draft animals, and made poultices for scratches, wounds, sores, and bruises. It is particularly good for encouraging healing of difficult abrasion wounds.
Indians dried and powdered creosote leaves and rubbed them on infant’s navals to promote healing. Women used decoctions to relieve premenstrual cramps and made beds of fresh branches and leaves to relieve birthing pains.
Even today, people use this plant. The FDA discourages the use of “Chaparral” (dried leaves ground to a powder) because of reported toxicity to the liver, people still make teas for arthritis, sore throats, and respiratory infections and use decoctions externally for the same purposes as natives used it thousands of years ago.
Desert hikers and other desert lovers would be well advised to learn more about this remarkable plant – it can bring a world of relief to anyone injured or unwell and far from modern medical care.