Creosote: The Oldest on Earth

One of the most widespread plants in the Mojave and Sonoran Deserts is the creosote bush, which nourishes its own interdependent set of creatures. Remarkably, the creosote might live longer than any other plant on the planet, nearly 12,000 years. That is remarkable considering the low, olive-green bush with tiny leaves thrives in areas too tough for almost any other plant. A biologist working in the Mojave Desert noticed what seemed to be a great ring of creosote bushes. Intrigued, he took samples of plants all around the circle and also dug up some fragments of wood from a mound in the center of the circle. He discovered that all of the bushes in the circle were genetically identical. Then he discovered that the wood in the center of the circle was nearly 12,000 years old. From this, he concluded that the creosote bushes growing around the ring were offshoots from the roots of that original plant, which means the original plant was still alive and still flourishing as many connected bushes after 12,000 years. There is something encouraging about the idea that a plant clinging to survival in such a hard place and growing only an inch a year could through sheer persistence hang on to become the world’s oldest living thing.

Remarkable adaptations enable the creosote to survive in places where it does not rain for a year at a time and summer temperatures soar to 130?F (54?C). The creosote can send roots down 150 feet (50 m) to find groundwater. Normally, the moisture difference between roots in groundwater and the sun-blasted leaves of a plant create a pressure difference between root and leaves called osmotic pressure. The creosote can stand a greater pressure difference between leaf and root than any other living plant, which means it can draw water from deeper in the soil without rupturing the cells that feed the water to the leaves. The leaves also have many chemicals that protect them from the sun, dehydration, and insects. These chemicals can also serve as a natural herbicide, to keep other plants from growing too close and competing for the scarce water. Native Americans learned to use some of these substances for medicines, sealants, glue, and other purposes. They also made adroit use of the insects that made use of the creosote; for instance, they used a protective chemical secreted by a flat, scale insect that lives only on creosote to mend pottery, waterproof baskets, and glue arrowheads.

Many other desert dwellers have also developed ways to deal with those defensive plant chemicals and make full use of the creosote. The creosote bagworm moth lays her eggs in the small leaves of the creosote then stitches the leaf together with silk. The larvae eventually hatch and promptly make a meal of their leafy home. The archenemy of the creosote bagworm is the bracconid wasp, which looks for these sewn-together creosote leaves and then lays her own eggs on top of the moth larva. The hatching wasp larvae consume the bagworm moth larvae before they get a chance to dine on creosote leaf, which provides a glimpse of the ecological complexity of such crucial plants in so hard a place as a desert.