plant. The generic name commemorates the eminent botanist, Dr. Frederick 

 V. Coville. The specific name tridentata describes the stamen stalk. 



This shrub ranges from California eastward through southern Nevada and 

 southwestern Utah, to southern Colorado and western Texas, and south into 

 Mexico. It covers many thousands of square miles in pure stands or in asso- 

 ciation with bur-sage (Franseria dumosa), its very common companion, and 

 various other shrubs. Creosotebush is so characteristic of certain large areas 

 as to constitute a distinctive vegetative unit, called the creosotebush, or Covttlea, 

 association. Shantz (in Tidestrom J ) reports that this association is more exten- 

 sive than any other type of vegetation in the southern desert. This belt, in 

 which creosotebush is so common, is designated by some plant ecologists as the 

 Lower Sonoran Zone. Scientific observers classify the creosotebush association 

 as one of the most permanent types of vegetation. Creosotebush occurs on the 

 sandy or gravelly soils of mesas and hillsides, but attains its maximum develop- 

 ment on pervious soils of flats and alluvial fans, where its deep-seated roots 

 obtain adequate moisture. The resinous covering of its stems and leaves mini- 

 mizes transpiration and protects the plant against drought. The species has 

 long attracted the attention of plant physiologists, and numerous technical 

 papers have been published on its remarkable adaptation to severe climatic and 

 soil conditions. Runyon 2 calls it "the most successful and conspicuous xerophyte 

 (i. e., dry-land plant) in the desert regions of North America." Spalding' ascer- 

 tained that creosotebush has become especially well adapted to dry conditions by 

 the development of numerous root hairs and a very high osmotic pressure within 

 the plant cells, which give it exceptional power in water absorption. He further 

 determined that, although it has acquired capacity for withstanding excessive 

 drought, it attains its best growth where the water supply is favorable. 



Creosotebush is important chiefly because of its abundance, as it is the dom- 

 inant vegetation on large areas, where it serves as an efficient soil protector 

 and stabilizer. However, it is not a good soil builder, and does not facilitate 

 the growth of better plants upon the sites where it occurs abundantly. This 

 species is worthless as forage at all seasons and to all classes of livestock. 

 Usually, very little palatable vegetation grows in a true creosotebush type; 

 hence the carrying capacity of such areas is either very low or nil. Livestock 

 even avoid it during drought, unless absolutely forced to eat it rather than 

 starve. Griffiths * reports that sheep are poisoned by this plant when com- 

 pelled to eat it during years of forage scarcity, and that the greatest mortality 

 occurs among pregnant ewes. Crawford, 5 however, determined that liquid 

 extracted from the leaves of creosotebush and given to sheep and rabbits pro- 

 duced absolutely no undesirable results ; he states that the belief among stock- 

 men as to the poisonous effects of this plant is unfounded. 



Creosotebush has a prominent place in the mythology of the Pima Indians of 

 the Southwest. 6 The reddish brown resin which is deposited on the branches by 

 the scale insect Tachardtella (syn. Carteria) larrcac was used by the Indians for 

 mending pottery, cementing arrow heads, coating baskets, etc. The leaves and 

 twigs were used, in decoction, as a tonic and antiseptic. 5 6 7 



Creosotebush is a much-branched shrub from 3 to 11 feet high. As a rule, 

 it often naturally occurs so widely and uniformly spaced as to convey the im- 

 pression that the plants have been set out artificially in almost military aline- 

 ment. The gray stems are banded in black at the nodes and spread out grace- 

 fully from the ground, forming a rather broad flat top. The yellow flowers 

 mature rapidly and are soon replaced by the fuzzy, white seed balls. 



1 Tidestrom, I. FLORA OF UTAH AND NEVADA. U. S. Natl. Mus., Contrib. U. S. Natl. 

 Herbarium 25, 665 pp., illus. 1925. 



2 Runyon, E. H. THE ORGANIZATION OF THE CREOSOTE BUSH WITH RESPECT TO DROUGHT. 

 Ecology 15 (2) : 128-138, illus. 1934. 



3 Spalding, V. M. BIOLOGICAL RELATIONS OF CERTAIN DESERT SHRUBS, i. THE CREOSOTE 



BUSH (COVILLEA TRIDENTATA) IN ITS RELATION TO WATER SUPPLY. Bot. Gaz. 38 I 122-138, 



illus. 1904. 



4 Griffiths, D. RANGE INVESTIGATIONS IN ARIZONA. U. S. Dept. Agr., Bur. Plant Indus. 

 Bull. 67, 62 pp., illus. 1904. 



5 Crawford, A. C. NOTES, MAINLY BIBLIOGRAPHICAL, ON TWO AMERICAN PLANTS SLEEPY 

 GRASS AND CREOSOTE BUSH. Pharrn. Rev. 26 : 230-235. 1908. 



"Russell, F. THE PIMA INDIANS. U. S. Bur. Amer. Ethnol. Ann. Rept. (1904-5) 26: 

 3-[390], iilus. 1908. 



7 Kunze, R. E. THE DESERT FLORA OF PHOENIX, ARIZONA. Bull. Torrey Bot. Club 30: 

 302-307. 1903. 



