|Plants and Flowers
The northeastern portion of the Sonora desert, the Arizona upland desert, is home to the giant saguaro (or sahuaro) cactus that has become the symbol of Arizona. Most of this desert is to the west of Tucson. To the east the land gradually climbs to a higher elevation and few, if any, saguaros are actually natives of Cochise County. As you drive east from Tucson along interstate highway 10 you can almost spot the line where the saguaros stop.
In Cochise county the upland desert merges and blends into rocky semiarid steppe lands. Most of the common wild plants are xerophytes, plants that are specially adapted to succeed in an arid climate. They are typically able to withstand long periods of drought and the drying effects of desert winds.
There are a number of strategies which xerophytic plants may use to adjust to their environment. They include: dormancy, water storage, dwarfing, and modifications for water conservation.
DORMANCY: Many of the smallest plants of the desert use the dormancy strategy. An annual plant such as a poppy or caltrop may remain in the seed stage until sufficient rain has fallen, then it sprouts, grows rapidly to maturity and produces seeds which will lie dormant in their turn until conditions are again favorable. Sometimes they may remain dormant several years. Other plants that appear only after rains may actually have tubers or bulbous roots deep in the ground. These can also remain dormant until there's a season of deep-watering rains.
WATER STORAGE: Some plants have adapted to arid lands by developing the ability to store water. The most impressive of these, apart from the giant saguaro, is surely the century plant or agave, which has thick, leathery leaves that can be more than four feet long. These leaves grow from a large central core about the size of a large pumpkin that maintains moisture. The leaves are curved in such a way that they funnel any rain or moisture that strikes them down to the base of the plant. Agave roots also are bulbous and contain moisture, allowing the plant to survive months and even years without rain.
DWARFISM: Many plants succeed in the desert by remaining much smaller than they would be in temperate climates. The many, widely-separated little bushes and shrubs that often accompany mesquites are using this strategy--keeping a low profile and not requiring much water.
Mesquites themselves, of course, are masters of low water use. They leaf out last of any of the desert trees, usually waiting until May before coming into leaf and blooming. Their small leaves provide only minimal surface area for evaporation and their long taproots go deep into the soil, often as much as sixty feet. The fact that their seeds provide reliable food even in the dry years makes them especially valuable as a source of food for wildlife in times when other food might be scarce. Mesquites rank as the third most important wildlife food source in the mountain/desert area (behind pine and sagebrush).
MODIFICATION OF PARTS: In the succulent plants known as cacti the stem has taken over leaf functions and generally has a thick woody or waxy casing to prevent water loss. These chlorophyll-bearing stems perform photosynthesis for the plant. Cacti are different from other succulent plants in having small, cushionlike structures called areoles. It is from these areoles that the spines or bristles arise. Large colorful flowers are followed by fruit. In some species, such as the prickly pear, the food is a valuable source of food for wildlife. (See photo at the top of this page.)
All of these characteristics of xerophytes make the plantlife of the semiarid steppes an ever-changing wonder. No two springs are the same, even in the exact same spot. One year the yuccas will be king, the next the cholla cactus will steal the show with their delicate purple flowers and another year heavy winter rains may cause fields of golden poppies to spread across the land.
Heavy winter rains in 2009-10 brought forth a fabulous season of yucca, the most yucca blooms in recent history. I think every yucca plant in Cochise County bloomed this June. This was followed by the bountiful monsoon rains of the July and August 2010 that produced a wealth of summer wildflowers. The native grasses grew tall; golden poppies were everywhere and the daturas, shown above, were large and healthy. Alas this also meant an abundant crop of tumbleweeds....
Bowers, Janice Emily. Shrubs & Trees of the Southwest Deserts. Tucson: Southwest Parks and Monuments Assoc., 1993.
Bowers, Nora and Rick. Cactus of Arizona Field Guide (Arizona Field Guides). Cambridge, MN: Adventure Publications, Inc., 2008. This book classifies cacti by stem type rather than flower appearance as many plant guides do. This is helpful in identifying plants when not in flower. Stems are broken down into Cylindrical, Segmented, Stick-like, and Columnar, with varieties being grouped within each type: e.g. pincushion, barrel, hedgehog, cholla etc. This is a handy method of working and many varieties of each type are further described with close-up photos. An excellent guide to the cacti of Arizona. All the books in this series from Adventure Publications are a handy 4 1/4" by 6" size, perfect for carrying while hiking or biking.
___________________. Wildflowers of Arizona Field Guide (Arizona Field Guides). Cambridge, MN: Adventure Publications, Inc., 2008. This book identifies wildflowers by their blossoms and, like most of these guides, doesn't help much if your specimen isn't blooming. If you have a flower to work with, however, it is an excellent guide with a full-page photo and exellent descriptive material. All the books in this series from Adventure Publications are a handy 4 1/4" by 6" size, perfect for carrying while hiking or biking.
Epple, Anne Orth. A Field Guide to the Plants of Arizona . Helena, MT: Falcon Publishing, Inc., 1995.
Jaeger, Edmund C. The North American Deserts. Stanford: Stanford University Press, 1957. An older book but well worth seeking out; try your library or a used book dealer.
Larson, Peggy Pickering. The Deserts of the Southwest: A Sierra Club Naturalist's Guide (Sierra Club Naturalist's Guides). 2nd edition. San Francisco: Sierra Club Books, 2000.
Martin, Alexander C. et al. American Wildlife and Plants: A Guide to Wildlife Food Habits. New York: Dover Publications, 1961.
Tekiela, Stan. Trees of Arizona Field Guide (Arizona Field Guides) . Cambridge, MN: Adventure Publications, 2008. In addition to excellent photos, this book provides information on leaves or needles, bark, mature size, fall color, and range within the state for 90 common Arizona trees. All the books in this series from Adventure Publications are a handy 4 1/4" by 6" size, just right for carrying while hiking or biking.