San Francisco State University
Department of Geography
Geography 316:  Biogeography

The Biogeography of Agave deserti
by Scott Kress, student in Geography 316, Fall 2000


Photo by Professor Howard Towner (Ref.#1)

Kingdom: Plantae
Division:  Magnoliophya
Class:       Liliopsida
Order:      Liliales
Family:    Agavaceae
Genus:    Agave
Species:   Agave deserti

Introduction
     The beauty of the desert Agave is only an accent to the wealth of resource this plant possesses. Contemporary North Americans (like myself) probably associate the Agave with making tequila or its use as an ornamental but there is much more to this species. On the most basic level this plant will aid the weary desert inhabitant - Life!- from moisture stored in the plump, gelatinous leaves to the sweet nectar of long awaited blooms. The desert agave is an oasis to desert dwellers and ultimately the key to survival  for many species, including humans. Pre Agricultural man in the American Southwest relied heavily on the desert agave for year-round food and drink. Likewise, populations and migrations of birds, mammals and insects were shaped by the presence of these plants.
    In the United States, species of Agave are commonly known as "century plants" because of the erroneous belief that the plants only flower every hundred years. This belief is probably based on the fact that in cultivation, many species rarely bloom. Under favorable conditions, the life cycle of an agave is 10 - 12 years (Brietung, 1968). Surprisingly the agave is considered an annual because after blooming once, the plant withers and dies.

Description

The genus Agave, which means "noble" (from the Greek word agaue), and was first described by Carolus Linnaeus. In 1753, he named its first species, Agave americana. Since then many well known European taxonomists have studied the agave and added many new varieties. However, it was not till the work of  Howard Scott Gentry did a thorough study appear. Gentry spent over twenty-five years traveling the world studying and collecting desert plants, agave in particular. Although he relied to some extent on the works of taxonomists William Trelease and Alwin Berger, Gentry  introduced important new concepts in nomenclature which allowed him to revise quite extensively the available data on agaves (Kolendo, 1996). As a result of his work Gentry has been regarded as the foremost expert in this particular field. In his book 'Agaves of Continental North America' published in 1982, Gentry identifies Agave deserti.
    Agaves represent a large genus of about 136 species of leaf succulents in the family Agavaceae, which has about twelve genera and 250 species. The genus can be readily separated into distinct subgenera: Littaea with spicate or racemose flowering forms and Agave with inflorescences of spreading umbellate or paniculate branches (Nobel, 1994). Within Agave, the group Deserticolae has 10 known species, which A. deserti falls under.
    This writer has not visited the A. deserti in its native habitat and does not have the taxonomic background to give a complete physical description. For this reason I have included Gentry's complete description of A.deserti as it relates to general morphological characteristics of the Agave genus;  "Plants small- to medium sized, glaucous gray to greenish, freely suckering, or medium sized to large, green, nonsurculose, the rosettes acaulesent to short caulesent; leaves rigid, coarsley fibered, with thick cuticle, narrowly lanceolate and with weak, easily detached teeth, or broader and with firmer teeth; panicle narrow with short lateral branches, dry scarious peduncular bracts, and small umbellate flower clusters; flowers small with very short open tube, the sepals about equal and 3 to 5 times as long as the tube; spring flowering; capsules small to medium, freely seeding" (Gentry, 1982). 

Distribution
  A. deserti is native to the rocky or gravely soils in the Lower Colorado River Valley subdivision of the Sonoran Desert. Its range extends barely into Arizona upland and the Mohave Desert. The Group Deserticolae occupy a large area around the Gulf of California, nearly throughout the Sonoran Desert. Agave deserti concentrations can be found in the high deserts of Southern California, Arizona and northern Baja, Mexico. In California you will find A. deserti in the Anza Borrego Desert, Palm desert and on the arroyos below the western slopes of  the San Bernardino Mountains. There is also a small concentration at a base level of the Providence Mountains in the Mojave Desert (Gentry, 1982). 

Map of Distribution:  
Map provided by CalFlora, 2000. Shaded areas indicate a presence somewhere within the area, and not necessarily presence everywhere within the area. Photo Ref.#2

Habitat
     As can be deducted by the taxonomic description, A. deserti is the most desert adapted of the agaves. Agave is generally found in the warm sub-tropics but A. deserti populations are found in the hottest, arid continental deserts of the sub tropic latitudes. Although literature describing specific habitat for A. deserti is extremely limited, inferences can be made by describing the sample locations mentioned in Gentry’s book.
      In his book a sample photo was taken along the San Felipe arroyo in San Diego County. The San Felipe arroyo lies in the rain shadow created to the east of the Palomar Mountains at an elevation of approximately 1650 feet. In this xerophitic habitat total annual rainfall ranges from less than 5 inches to no more than 10 inches (Bowman, 1973); for long periods there may be very little precipitation. This desert area has a wide range of seasonal and daily temperatures. The mean maximum temperature in July is between 100°F and 105°F, and the mean minimum in January is 36° F. Winds are generally light; in fact, less than 8 miles per hour 64 percent of the time (Bowman, 1973).
   Soils along the slopes in this region show little soil development and consequently have little vegetative cover. For this reason when precipitation does occur there is a high amount of erosion which washes the sediments into the arroyos below. San Felipe arroyo is made up of young granitic alluvium occurring in broad basins, on alluvial fans. The soil is very gravely sand to loamy coarse sand in texture and is fairly well sorted (Bowman, 1973). It is on these deposits where you will find A. deserti.

Limiting Factors
  A. deserti is a product of the hot arid continental desert with high insulation and more extreme circadian temperature changes (Gentry, 1982). When you compare A. deserti with other species of agave such as Agave cerculata limiting factors may be inferred. Agave cerculata is primarily a product of the upland maritime environment where frequent fogs and ocean breezes temper the desert climate and soils are well developed. A. deserti has adapted to the low precipitation, hot, arid areas of the interior deserts with poorly developed high drainage soils. Limiting factors therefore may include the need for alkaline gravely soils, low humidity/precipitation and no shade cover.

Agave cerculata
Photo by Julia Etter & Martin Kristen (Ref.#3)		 Agave deserti
 Photo by Julia Etter & Martin Kristen (Ref.#4)

                      
Reproduction
      Just how ancient desert agaves radiated is still not fully understood. The most efficient method of re-generation observed today is the spreading of plants through rhizomes underground. As spent rosettes of wild plants die and decompose, new ones replace them on the outer margin, eventually forming ring-shaped colonies. Rings 20 feet (6 m) in diameter in California's Anza-Borrego Desert State Park may be more than a millennium old (Dimmitt, 2000).
     Pollination and seed production though less productive does occur and the primary pollinator is Leptonycteris sanborni, the desert bat. A. deserti emits a musky smell produced from butyric acid that these bats find hard to resist. On annual migrations from Mexico flocks of bats stop to feed on blooming agave. The symbiotic relationship between these two species is so finely tuned that the agave produces in its nectar two amino acids it doesn't need but which are essential to the bat; proline for building muscle tissue, and tyrosine, used by lactating mothers as a growth stimulator for their young (Heacox, 1989). Some scientists believe that without bats wild desert agaves might not reproduce.
     Blooms of the agave are considered "perfect", that is , they have both male and female parts so pollination is easily attained. Having this advantage, agave makes the most of its one flower that may not appear for twenty years. These plants also know how to advertise, they produce flower stalks that can reach fifty feet!


Leptonycteris sanborni feed on Agave bloom.
 Photo by Merlin D. Tuttle (Ref.#5)

Natural History
     It has been has been stated that agaves were outranked only by maize and potatoes in use by the early Aztec, Maya and other Indians of Mexico (Breitung, 1968). Agaves use as a food source dates back at least 9000 years.Coprolite study of a nine thousand-year-old mummified human body, discovered in a Northern Mexico cave, detected agave fragments and fibers (Kolendo, 2000).
     Barrows (1967) stated that the Coahuilan Indians of Southern California made much use of A. deserti. They called the plant "a-mul", sections of the flowering stalk "u-a-sil", the leaves "ya-mil", and the yellow blossoms  "amul-sal-em", all of which were cooked in various ways and eaten. Briefly, the utilization of this species has included; food, drink, soap, clothing, rope, and other fibers, needles and thread, paper, glue, weapons, medicines, red coloring matter and ornamental and hedge plants. As Howard Scott Gentry put it "The uses of agaves are as many as the arts of man have found it convenient to devise". 

Evolution
    For over 200 million years angiosperms have undergone changes and developments that have led to various recognizable groups of plants. Each species took on adaptive responses that led to particular lines of evolution of plant groups. The line that led to the agave, a monocotyledon, originated in the early Tertiary about 60 million years ago. The radiation of the agave took place more recently, probably 30 to 35 million years ago (Nobel, 1994). Through fossil records and distribution of present day agaves, the radiation of this species appears to have originated in southern Mexico or northern South America. Initially it was thought that perhaps Central America was a likely place of origin but shift in tectonic plates near the earth’s surface had not yet created Central America at that time (Nobel, 1994).
    Many centuries of mythical lore and spiritual attachment by early mesoamericans followed the discovery of the agave's usefulness (Jan Kolendo has written a great article on the Agave's mythological past and its cultural influences called, The Agave: A Plant and its Story - referenced in Bib.).
     As human populations have increased, economic gain from agave products has increased its importance to native peoples. Although easily cultivated, many rural inhabitants in agave regions have begun to harvest wild agaves. Production of bootleg mescal (a harsh version of Tequila) has become profitable and as a result, its been estimated that up to a half-million agaves are uprooted each year in illegal harvests. These harvests have no doubt limited the natural radiation of agave and impacted heavily a wide variety of animals and insects. Bats populations in particular have been decreasing dramatically which could further reduce the presence of wild agave. "That any wild agaves remain at all might be due largely to their rugged, inaccessible habitat" (Heacox,1989).

Conclusion
Agave deserti is wonderful reminder of how well species can adapt. Its ability to retain moisture and flourish in harsh climates is a lesson in adaptability. The soft leaf texture, soothing colors and beautiful flowers of Agave create one of the arid deserts most alluring attractions. What I found surprising is the lack of scientific study and general information available on desert agave. A plant so significant to successive civilizations of native North Americans should not be taken for granted and left to its demise. It is becoming clear that without protection this species could disappear. References Breitung, August L. 1968, “The Agaves – The Cactus and Succulent Journal 1968 Yearbook” Cambridge Press 1968

Bowman, Roy H.  1973, Soil Survey - San Diego Area, California Part I. United States Department of Agriculture. Soil Conservation Service and Forest Service in cooperation with Univ. of California Agricultural Experiment Station. United States Dept. of the Interior.

CalFlora, 2000, Map of distribution - CalFlora Database-Distribution Data. Available on-line @ http://www.csdl.tamu.edu/FLORA/cgi/calmap?n=114 - Accessed 11/09/00.

Dimmitt, Mark A. 2000, “A Natural History of the Sonoran Desert” Available on-line @ http://www.desertmuseum.org/natural_history/agavaceae.html#deserti - Accessed 11/19/00.

Gentry, Howard Scott 1982, “Agaves of Continental North America” pg.354. The University of Arizona Press 1982.

Heacox, Kim 1987, The Beautiful, Beleaguered Agave – Pacific Discovery magazine July-Sept. 1987

Heacox, Kim  1989, “Fatal Attraction” - International Wildlife magazine May-June Vol.19, No 3.

Kolendo, Jan  2000, “The Agave: A Plant and its Story” Available on-line @ http://www.users.globalnet.co.uk/~jankol/articles/articles.html - Accessed 11/04/00.

Nobel, Park S. 1994, “Remarkable Agaves and Cacti ,University of California Los Angeles  1994” – Oxford University Press.

Photos 1. (date ?) Taken by Dr. Howard F. Towner, PhD.   Prof. of Biology, Loyola Marymount University.

2. 1998  Taken by Henriette Kress.  Available on-line @ http://www.ibiblio.org/herbmed/pictures/pic-a.html  Accessed 12-02-00.

3. (date ?) Taken by Julia Etter & Martin Kristen.  Available on-line @ http://globetrotters.ch/globetre_ie.html  Accessed 11-29-00

4. (date ?) Taken by Julia Etter & Martin Kristen.  Available on-line @ http://globetroters.ch/globetre_ie.html  Accessed 11-29-00

5. (date ?) Taken by Merlin D. Tuttle.  Available on-line @ http://www.batcon.org/batsmag/v5n4-4.html  Accessed 12-01-00

Other Resources
Stebbins, G. L., and J. Major. 1965. Endemism and speciation in the California flora. Ecological Monographs 35:1­35.

Raven, P. H. 1977. The California flora. Pages 109­137 in M. G. Barbour and J. Major, editors. Terrestrial vegetation of California. John Wiley & Sons, New York.

Raven, P. H., and D. I. Axelrod. 1978. Origins and relationships of the California flora. University of California Publication in Botany 72:1­134.

Wilken, D. H. 1993. California's changing climates and flora. Pages 55­58 in J. C. Hickman, editor. The Jepson manual: higher plants of California. University of California Press, Berkeley and Los Angeles.
 

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