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ACACIAS 



Aca'cia spp. 



The acacias belong to the mimosa family (Mimosaceae), which 

 some authors include as a subfamily of the immense legume family 

 (Leguminosae), and are widely distributed throughout the tropics 

 and subtropics and also occur in some temperate regions. Most of 

 the 400 or more species are native to Australia and Africa ; about 16 

 species occur naturally in the West, and the genus is well represented 

 in Mexico. Except for a few herbaceous species, acacias are trees 

 or shrubs j they have either bipinnately compound leaves or ap- 

 parently simple leaves (the latter are not actually leaves but, rather, 

 leaf like petioles known as phyllodes, no true blade being present). 

 The small, numerous, usually orange-yellow (sometimes lemon-yel- 

 low or white) flowers are borne in dense heads, spikes, or axillary 

 racemes. 



The acacias are an important source of valuable forest products, 

 including gums, dyes, tannins, medicines, perfumes, lac, fibers, and 

 timber. Many of the species with low tannin content are useful as 

 browse. For example, the leaves and young shoots form the principal 

 browse for goats and camels on African and Asiatic deserts, and 

 certain species in Australia furnish considerable browse for cattle, 

 sheep, and other livestock. 1 Probably all the acacias native to the 

 United States have some forage value, with catclaw, which is written 

 up separately in this handbook, the most important, although the 

 palatability of their herbage is usually low to fair. The pods of 

 acacias are likely to be too bitter, too tough, or both, to be attractive 

 to domestic livestock. In Africa certain species (such as A. giraffae) 

 are the favorite food of the giraffe, and Darwin deduced that the 

 development of the elongated neck of this animal was the result of 

 its ancestors' efforts to crop the foliage of these acacia trees. Ca- 

 techu, the well-known astringent of modern medicine, is obtained 

 from an acacia of Hindustan. A number of species are cultivated as 

 ornamentals. Certain tropical American species, known as bullhorn 

 acacias, are interesting examples of entomophily, the spines being 

 converted into ant chambers, the ants, in turn, protecting the trees 

 from grazing animals and other invaders. 2 



Probably no other semitropical trees of high economic value sur- 

 pass the acacias in ability to thrive upon and even improve many 

 arid and sterile soils. Although only half hardy to frost, these 

 plants grow well under such restricted precipitation as only a few 

 inches of rainfall annually. The late C. H. Shinn, 1 a former 

 Forest Service supervisor, has called attention to the value of acacias 

 for ocean sand dune and inland sand barren reclamation, under 

 arid and semiarid conditions where the temperature does not fall 

 below 20 F. He states that there are about 40 species well adapted 

 to hedge use and for shelter belts in areas of brisk winds and high 



1 Shinn, C. H. AN ECONOMIC STUDY OP ACACIAS. U. S. Dept. Agr. Bull. 9, 38 pp., lllus. 



2 Safford, W. E. ANT ACACIAS AND ACACIA ANTS op MEXICO AND CENTBAL AMERICA. 

 Smlthsn. Inst. Ann. Kept. 1921 : 381-394, lllus. 1922. 



