  Many people think of a desert as an area of shifting sand dunes without vegetation except in areas where springs provide moisture. This is by no means true of our Southwestern deserts which are characterized by a rich and diversified plant cover. However, the majority of true desert plants are equipped by Nature to meet conditions of high temperatures and deficient and uncertain precipitation. The way in which desert plants, closely related to common species found growing under normal temperature and moisture conditions, have adapted themselves to meet the severe requirements of desert life is truly remarkable and forms an absorbing and fascinating study. Shreve groups desert plants into three categories based on the manner in which they have contrived to conquer the hazards of desert life. These are:
Drought-escaping plants are the “desert quickies,” or ephemerals. Taking advantage of the two seasons of rainfall on the desert (midsummer showers and midwinter soakers) they develop rapidly, blossom, and mature their seeds which lie dormant in the soil during the rest of the year, thus escaping the season of heat and drought. There are two groups of these “quickies,” the summer ephemerals and the winter ephemerals. The former are hot-weather plants; the latter are species that thrive during the cool, moist weather of winter and early spring. These “quickies” present their spectacular floral displays only following seasons of above-average precipitation. Drought-evading plants (in common with the deciduous plants of northern and colder climes which remain dormant while below-freezing temperatures prevail), meet the heat and drought by reducing the bodily processes to maintain life only, dropping their leaves, and remaining in a state of dormancy until temperature and moisture conditions, suitable to renewed activity, again prevail. The drought-resisting plants are the bold spirits which take the worst that the desert has to offer without flinching, or resorting to evasive tactics. Chief among these are the cacti which store moisture in their spongy stem or root tissues during periods of rainfall, using it sparingly during drought. To reduce moisture loss to a minimum, they have done away with their leaves, the green skin of their stems taking over the function of foliage. Other plants, such as the Mesquite, develop deep or widespread root systems that extract every drop of moisture from a huge area of soil. The majority of the drought-resisters either cut down their leaf surface to an irreducible minimum, or coat the leaves with wax or varnish, thus restricting the loss of moisture. Methods, techniques, devices, or body modifications which desert plants have developed or evolved to enable them to withstand the rigors of long-continued drought and heat are legion. Many of them are known and understood, but it is probable that there are many others which scientists have not yet discovered. |
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