42 University of Texas Bulletin 



Xanthoxalis stricta Small. (Oxalis stricta L.) 

 Yellow Wood Sorrel. Sour Grass. 

 University campus, etc. 

 Widesspread in eastern and central North America. 



Xanthoxalis. (Oxalis Wrightii Gray.) Wood Sorrel. Sour Grass. 

 University campus, etc. 

 West Texas. 



ZYGOPHYLLACEAE Caltrop Family 



Kallstroemia intermedia Vail. Caltrop. 



Dry waste ground. Abundant on the campus. A prostrate plant 

 with yellow flowers and legume-like compound leaves. 



Southern plains and prairie states and Mexico. 



Tribulus terestris L. Caltrop. Bur Nut. 



Along railroad tracks. Its angled, spiny fruit makes it a very 

 troublesome weed wherever abundant. Similar to Kallstroemia ex- 

 cept in fruit. 



Introduced into America and now widespread. 



RUTACEAE Rue Family 



Fagara Clava-Herculis Small. (Xanthoxylum Clava-Herculis L.) 

 Prickly Ash. Tootache Tree. 



Banks of Onion Creek and similar situations. Characterized by its 

 tuberculate, thorny trunk. 



Southeastern states. 



Fagara fruticosa Small. (Xanthoxylum carolinianum var. fruticosum 

 A. Gray.) Prickly Ash. 



A thorny shrub abundant on hillsides, and easily recognized by its 

 glossy compound leaves and strong odor. 



Arkansas and Texas. 



Ptelea trifoliata L. Hop Tree. Skunk Bush. 



One of our most abundant shrubs in ravines and valleys. Easily 

 recognized by its peculiar odor and its round, flat fruits and trifoliate 

 leaves. 



Eastern North America. 



Thamnosma texana Torr. 



Abundant on barren, rocky slopes of the Edwards Plateau. A low 

 partly shrubby plant with small strong scented leaves and two-lobed 

 fruits. 



Texas to Mexico. 



