Tribulus. ZYGOPHYLLACE.E. 91 



ORDER XXIII. ZYGOPHYLLACE^I. 



Distinguished from the allied orders by the opposite compound leaves, with in- 

 terposed stipules and entire dotless leaflets. Flowers perfect, regular or nearly so, 

 completely symmetrical, the parts in fives or rarely in fours. Sepals distinct or nearly 

 so. Petals hypogynous, in ours imbricated in the bud. Stamens as many or more 

 commonly (in all ours) twice as many as the petals and inserted with them, in two 

 sets : filaments distinct, often appendaged with a scale on the inner side. Ovary of 

 4 or 5 carpels (rarely 2 or 3), but sometimes twice as many cells, and terminal style 

 only one : stigma 5- 10-lobed. Ovules anatropous, pendulous. Fruit dry. Seeds 

 with a large embryo, straight or nearly so, with flat or broad cotyledons, with or 

 without some albumen. Herbs, shrubs, or (in Guaiacum) small trees, with very 

 hard and acrid-bitter resinous wood; a few with simple leaves : stipules often 

 spinescent: flowers solitary, on lateral or terminal naked peduncles. 



An order of 17 genera and barely a hundred species, of tropical and warm -temperate countries, 

 on this continent chiefly Mexican and South American, four representatives, belonging to three 

 genera, barely reaching California. 



1. Tribulus. Leaves abruptly pinnate, 6-10-foliolate. Fruit tuberculate. Herbs. 



2. Fagonia. Leaves 3-foliolate. Fruit nearly smooth. Herbaceous. 



3. Larrea. Leaves 2-foliolate. Fruit densely hairy. A heavy-scented shrub. 



1. TRIBULUS, Linn. 



Sepals 5, mostly persistent. Petals 5, fugacious. Disk annular, 10-lobed. 

 Stamens 10 ; the alternate filaments a little shorter and with a gland at base on the 

 outer side. Ovary 5-12-celled; cells 1-5-ovuled. Fruit lobed, separating from 

 the persistent axis into 5 to 12 indehiscerit 1-seeded tuberculate or winged or 

 spinose carpels. Seeds without albumen. Loosely branched hairy prostrate herbs ; 

 with abruptly pinnate opposite leaves (the alternate ones smaller or wanting), and 

 solitary apparently axillary white or yellow flowers. 



Species 15 or more, natives of the warmer regions of both hemispheres. Our species are 

 annuals, belonging to the section Kcdlstrcemiu, having the outer stamens adnate at base to the 

 petals, the ovary 10-12-celled and 10- 12-ovuled. A true Tribulus, with 5 carpels (T. Califor- 

 nicus, Watson, Proc. Am. Acad. xi. 125), from the western side of the Gulf of California, has 

 very small flowers and deeply 5-lobed fruit, the carpels with 4 or 5 stout tubercles on the back. 



1. T. maximus, Linn. Stems at length elongated : leaflets 3 or 4 pairs, ovate- 

 oblong, 3 to 6 lines long, more or less oblique: peduncles thickened upward, a half 

 to an inch long : sepals very hairy, linear, acuminate, two lines long : petals a half 

 longer : fruit two lines high, beaked by a stout style about as long ; the carpels 

 roughly tuberculate. Kallstrcemia maxima, Torr. & Gray, Fl. i. 213; Gray, Gen. 

 111. ii. 117, t. 146. 



"Southern California," Parry. Common in the diy region eastward to Texas, and through 

 Mexico and the W. Indies. The specific name is in no respect appropriate. 



2. T. grandiflorus, Benth. & Hook. Hispid with usually longer and more 

 spreading hairs : leaflets 4 to 6 pairs : peduncles more elongated : sepals 3 to 6 

 lines long, the petals usually twice longer : fruit rather more sharply tuberculate, 

 the beak 3 to 5 lines long. Gen. PI. i. 264. Kallstrcemia grandiflora, Torr. in 

 Gray, PL Wright, i. 28. 



In the Gila Valley, Arizona, and probably in Southeastern California ; ranging to New Mexico, 

 Sonora and Lower California. 



