DESCRIPTIVE MANUAL 



203 



Fig. 117-A. Distribution of Field Sorrel. 



Distribution. — A very common weed in dry or moist soil through- 

 out eastern North America. 



Extermination. — Apply the same method as to the preceding 

 species. 



ZYGOPHYLLACEAE, CALTROP FAMILY. 

 A small family. 



Caltrop (Tribulus terrestris L.) . 



Description.— The caltrop is a hairy, procumbent annual, branch- 

 ing from the base, producing a stem which is a foot or more long, 

 branches bear numerous small, compound leaves with short pe- 

 duncles ami small stipules at the base ; each compound leaf has 4-8 

 pairs of short-stalked leaves; small, yellow, axillary flowers about 

 1/2 in. across with peduncle much shorter than leaves; fruit very 

 spiny and divided into two nearly equal parts, each part consists of 

 2 long spines, 2 shorter and a row of very short ones, forming a 

 crest on the back ; 5-angled, spiny fruit splits into 3-5 divisions. 



Distribution. — Introduced from the Old World and occurs from 

 the Atlantic states to Nebraska and Kansas ; in Iowa has been found 

 only on Muscatine Island. 



Extermination. — Caltrop is disseminated by wool, and hence the 

 waste of woolen mills should not be thrown in fields. The weed is 

 easily destroyed by cultivation. 



