Naturalist View July 2010

Desert Plant Adaptations

 Last month, I wrote about how some of the animals of the desert adapt to the extreme temperatures and lack of water of their environment. Now let us look into some of the adaptations that allow plants to exist under the same harsh conditions. Like desert animals, desert plants have adapted to the extremes of heat and aridity using both behavioral and physical methods.

It has been said that desert plants survive because they have thorns, spines, taste bad or are poisonous. As true as this may seem, it’s not that simple. Anybody that has wandered in the desert has become aware of the plants’ defensive armor of thorns and spines. Most of us have had encounters with the “Jumping Cholla.” Of course, they really do not “jump,” but instead cling with their spines to anything that brushes ever so slightly against them. Many other desert trees and shrubs have also adapted by eliminating leaves and replacing them with thorns - or by greatly reducing leaf size. Such plants, like the Palo Verde, also usually have smooth, green (chlorophyll) bark on stems and trunks serving to both produce food and seal in moisture.

Xerophytes: Plants that have adapted by altering their physical structure are called xerophytes. Xerophytes, such as cacti, often have special means of storing and conserving water. They have few or no leaves; this reduces loss of water due to evaporation. Xerophytes are the largest group plants living in the deserts of the American Southwest. The Sonoran Desert is home to an incredible variety of succulents including the giant Saguaro Cactus, Mesquite, Paloverde, and Ironwood. A succulent can be defined as a plant that stores water in its tissues as a mechanism to survive periods of drought.

Phreatophytes: Plants that have adapted to arid environments by growing extremely long roots, allowing them to acquire moisture near the water table, are called Phreatophytes. A good example is the mesquite; its roots are the longest of any desert plant. Mesquite roots have been found in a copper mine shaft 160 feet beneath the surface. However, 90% of the roots of a mesquite remain in the top 3 feet of soil. The deep taproot helps the plant survive drought, while the surface roots are ready to soak up the scarce rainfall of the winter or the sudden downpour of the monsoon.

Two native mesquite trees, the Honey Mesquite and the Velvet Mesquite, are native to Saddlebrooke. Other species of Mesquite have been introduced into the area for landscaping. The Creosote bush is also one of the most successful of all desert species, because it utilizes a combination of many adaptations. Instead of thorns, it relies for protection on a smell and taste that wildlife find unpleasant. It has tiny leaves that close their stomata (pores) during the day to avoid water loss and open them at night to absorb moisture.

Other desert plants using behavioral adaptations have developed a lifestyle in conformance with the seasons of greatest moisture and/or coolest temperatures. These types of plants are referred to as perennials, plants that live for several years, and annuals, plants that live for only a season.
Desert perennials often survive by remaining dormant during dry periods of the year, then spring to life when water becomes available.
A familiar perennial is the Ocotillo. It survives by becoming dormant during dry periods, then coming to life when water becomes available. After rain falls, the Ocotillo quickly grows leaves to photosynthesize food. Flowers bloom within a few weeks in April When seeds become ripe and fall, the Ocotillo loses its leaves again and re-enters dormancy. During the summer monsoon the Ocotillo will often produce a new set of leaves but no new blossoms. The Ocotillo also has a waxy coating on stems which serves to seal in moisture during periods of dormancy.

Another example of perennials that utilize dormancy as a means of evading drought are bulbs, members of the lily family. The Coyote gourd has a bulb that springs to life after the summer monsoon, sending out 20 foot runners with yellow flowers that develop into the orange sized gourds. The fruit pulp contains toxic and extremely bitter chemicals that humans use to make soap, which reportedly repels body lice. Natives eat the nutritious seeds, which contain up to 35% protein and 50% fat. Coyotes and some other animals can eat the seeds even when tainted by the pulp. Javelinas eat tuberous roots, which they can sniff out even when there is no vine above ground. Native people have used the gourds as containers and dance rattles since prehistoric times.

Annuals (Ephemerals)
The term "annual" implies blooming yearly; but since this is not always the case, desert annuals are more accurately referred to as "ephemerals." Many of them can complete an entire life cycle in a matter of months, some in just weeks. Desert plants must act quickly when heat, moisture and light inform them it's time to bloom. Ephemerals are speedsters of the plant world, with flower stalks bursting out in a few days. The peak of this bloom may last for just days or several weeks, depending on the conditions. Most annual desert plants germinate only after heavy seasonal rain, and then complete their reproductive cycle very quickly. They bloom profusely for a few weeks in the spring, accounting for the annual wildflower displays of the deserts. Depending on the winter and spring rains, these displays can be spectacular or hardly noticeable. The seeds left behind that are not eaten by the birds, small mammals and insects may lie dormant for years until conditions are right for germination.

• Mesquite Tea: Place 1 lb. of mesquite pods in 1 gallon of water. Boil pods, at a rolling boil, for 30 minutes. Remove pods & strain. Cool broth & serve over ice.

• Mesquite BarBQ: All those mesquite pods lying around that need to be picked up can be used instead of expensive mesquite firewood or charcoal on your BarBQ. I recommend soaking the dry pods in water for 10-20 minutes then throw them directly on the briquettes or grill and cover to impart that mesquite flavor.

I have been very busy picking up pack-rats, mice etc. that residents have been live trapping and wish to thank you all for not using poisons. I only had one secondary poisoning in May, a dove that had feed on some poison seeds that had probably been intended for something else.