Part 2, 1910] ZYGOPHYLLACEAE 109 



leaflets obliquely lanceolate or lunate, curved or somewhat falcate, 5-10 cm. long, 2-3 

 mm. wide, inequilateral, thick, coriaceous, resinous, yellowish, with a broad attachment 

 to the rachis, silky-pubescent, becoming glabrate, more or less distinctly 3-ribbed ; peduncles 

 1 cm. long ; sepals round-ovate, obtuse, silky, the 2 outer nearly equal and smaller, the 3 

 inner unequal (1 smaller, 2 larger), broadly ovate, obtuse or truncate and often obscurely 

 toothed ; petals slightly unguiculate, the limb spatulate-oblong, obtuse or acute or acutish 

 and obscurely toothed, bright-yellow ; scales shorter than the filaments, variously 2-4- 

 toothed ; fruit subglobose or elliptic, 4-5 mm. broad, densely rusty-villous, beaked by the 

 slender style ; hairs longer than the width of the carpels ; carpels obtuse. 



Type locality : Olla and Fra Cristobal, New Mexico. 



Distribution : Utah to southern California, Texas, and northern Mexico. 



Illustrations : A. Gray, Gen. 111. 2 : pi. 147 ; Torr. in Emory, Notes Mil. Rec. pi. 3. 



2. Covillea tridentata (DC.) Vail, Bull. Torrey Club 26 : 302. 1899. 



Zygophyllum tridentatum DC. Prodr. 1 : 706. 1824. 



Carrea mexicana Moric. PI. Nouv. Am. 71. 1839. 



Larrea tridentata Coville, Contr. U. S. Nat. Herb. 4 : 75. 1893. 



A diffusely branched resinous shrub, similar in habit to the preceding; stipules reddish, 

 ovate or lanceolate, about 3 mm. long, caducous; leaves almost sessile; leaflets broadly 

 and obliquely ovate, 7-9 mm. long, about 5 mm. broad, 4-5-nerved, resinous, strigose or in 

 age glabrate ; peduncles 5-8 mm. long ; sepals elliptic, silky-strigose, rounded at the apex, 

 unequal ; petals yellow, short-clawed, about 8 mm. long, spatulate ; scales about half as 

 long as the stamens ; filaments 6 mm. long, filiform-subulate ; fruit broadly obovoid, about 

 6 mm. long and 5 mm. wide, tapering below into a distinct stipe, hirsute ; hairs 1-1.5 mm. 

 long. 



Type locality : Mexico. 



Distribution: Queretaro, Tamaulipas, San I.uis Potosi, and southwestern Texas. 



Illustrations: Moc. & Sesse, Calq. Dess. pi. 159 ; Naturaleza 2: pi. IS; Moric. PI. Nouv. 

 Am.pl. 48. 



5. TRIBULUS L,. Sp. PI. 386. 1753. 

 Diffuse herbs with weak often prostrate stems and branches. Stems pubescent, silky, or 

 hirsute. Leaves abruptly pinnate, opposite, one of each pair alternately smaller than the 

 other or sometimes abortive. Stipules lanceolate or subulate, membranaceous. Flowers 

 solitary on axillary peduncles. Sepals 5, lanceolate, herbaceous, soon caducous. Petals 5, 

 obovate, yellow, orange-colored, or rarely white, spreading, larger than the sepals, deciduous. 

 Stamens 10, hypogynous ; filaments filiform, naked, the 5 inner, alternate with the petals, 

 shorter than the outer, subtended by a small gland, sometimes sterile. Anthers cordate or 

 oblong. Ovary sessile, 5-celled, appressed-hirsute, surrounded at the base by an urceolate 

 10-lobed disk. Styles united into a short stout column. Stigmas 5, more or less connate, 

 parallel or somewhat radiate, papillose. Ovules 5-10 in each cell, superposed in a single 

 series, obliquely pendulous from the inner angle, anatropous. Fruit depressed, 5-angled, 

 tuberculate or spinose, separating at maturity into 5 bony carpels, leaving no central axis, 

 the carpels divided by oblique transverse septa into 3-5 one-seeded compartments. Seeds 

 oblong-obovate. Endosperm wanting. Testa membranaceous. 



Type species, Tribulus lerreslris h. 

 Peduncles longer than the leaves; plant perennial. 



Petals 1.5-2.5 cm. long. 1. T. cistoides. 



Petals 1-1.5 cm. long. 2. T. alacranensis. 



Peduncles shorter than the leaves ; petals about 4 mm. long ; plant annual. 3. T. lerreslris. 



1. Tribulus cistoides L. Sp. PI. 387. 1753. 



Tribulus lerreslris cistoides Oliver, Fl. Trop. Africa 1 : 284. 1868. 



A diffusely procumbent herb with thick woody root ; stems pubescent with appressed 

 or spreading hairs, many-striate, becoming glabrate; stipules subulate, 5-8 mm. long, at 

 length caducous; petioles shorter than the leaflets; leaves 1-5 cm. long; leaflets 6-8 pairs, 

 obliquely oblong or elliptic, acutish or obtuse, often mucronulate, 4-15 mm. long, silky- 

 pubescent beneath, the terminal pair somewhat smaller ; peduncles produced from the axils 



