518 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



61. BURSERACEAE. Touchwood family 



1. BURSERA. Elephanttree 



Shrubs or small trees, unarmed, strongly aromatic; young bark 

 smooth and brown, the older bark exfoliating ; leaves alternate, pinnate, 

 deciduous; flowers small, solitary or in very few-flowered clusters; 

 petals inserted on a ring-shaped disk; fruit drupelike, 3-angled, with 

 1 large bony seed. 



A resin called copal is obtained in Mexico from many of the species, 

 including B. odorata. It is used for cement and varnish, and for 

 treating bites of scorpions, etc. It is burned as incense in the churches 

 and was formerly so employed in the Aztec and Mayan temples. 



Key to the species 



1. Leaflets lanceolate, acute or acutish at apex, 15 to 40 mm. long, 4 to 15 mm. 

 wide; inflorescence several-flowered; pedicels often borne on a common 

 peduncle as long as or longer than themselves; young bark gray brown, the 

 old bark exfoliating in large thin sheets 1 . B. odorata. 



1. Leaflets narrowly oblong, oval, or spatulate (the terminal one sometimes 

 nearly orbicular), obtuse at apex, 2 to 8 mm. long, 1 to 2 mm. wide; inflores- 

 cence very few-flowered; pedicels with or without a common peduncle; 

 young bark red brown, the old bark exfoliating in flakes. 



2. B. MICROPHYLLA. 



1. Bursera odorata T. S. Brandeg., Calif. Acad. Sci. Proc. ser. 2, 2: 



138. 1889. 



Elaphrium odoratum Rose, North Amer. Fl. 25: 250. 1911. 



Known in Arizona only on dry limestone cliffs near Fresnal, western 

 foothills of the Baboquivari Mountains, Pima County (Gilman 3529, 

 etc.) , about 4,000 feet, July. Southern Arizona and Mexico (including 

 Baja California). 



The few plants at Fresnal, which reach a height of 4.5 m. (15 feet), 

 have the appearance of being survivors from a time when conditions 

 were more favorable to the species at this locality. The young bark 

 is bright green and the crushed herbage has an odor of tangerine peel. 

 The old bark can be removed in translucent sheets resembling parch- 

 ment. The branches yield quantities of gum, and when cut from the 

 tree dry very slowly. 



2. Bursera microphylla A. Gray, Amer. Acad. Arts and Sci. Proc. 5: 



155. 1861. 



Elaphrium microphyllum Rose, North Amer. Fl. 25: 250. 1911. 



Mountains of southwestern Arizona from the Salt River Mountains 

 (Maricopa County) to the Gila and Tinajas Altas Mountains (Yuma 

 County), 2,500 feet or lower, locally abundant on arid rocky slopes, 

 July. Southwestern Arizona, southeastern California, and Mexico. 



The trees reach a height in Arizona of 6 m. (20 feet) and a trunk 

 diameter of 0.3 m. (1 foot). The crooked branches taper rapidly and 

 resemble the trunk of an elephant. The plant cannot withstand much 

 cold. The bark contains tannin and was gathered in Sonora for 

 export. In that region the gum was used for treating venereal 

 diseases 



62. MALPIGHIACEAE. Malpighia family 



Plants suffrutescent ; stems trailing or twining; leaves simple, 

 opposite, with entire blades; hairs of the herbage appearing simple 



