306 RUTACEAE (RUE FAMILY) 



61. ZYGOPHYLLACEAE Lindl. BEAN CAPER FAMILY 



Herbs, shrubs, or trees, with opposite, pinnately compound, dotless, stipulate 

 leaves, symmetrical 4- or 5-merous flowers solitary on lateral or terminal 

 naked peduncles, stamens as many or twice as many as the petals, and a sin- 

 gle style terminating a 2-12-carpeled ovary which ripens dry. 



Herb; leaves with 6-10 leaflets . .1. Kallstroemia. 



Shrub; leaves with two leaflets 2. Covillea. 



KALLSTROEMIA Scop. CALTROP 



Pubescent branching herbs, with opposite, evenly pinnate leaves and sol- 

 itary, axillary, peduncled flowers. Sepals 5 (in ours), tardily deciduous. Pet- 

 als 5, early deciduous. Stamens 10. Ovary sessile, with 10-12 1-oyuled cells; 

 the style thick, striate. Fruit broad, crenately lobed, splitting into 10-12 

 1-seeded segments which are tubercled on the back. 



1. Kallstroemia brachystylis Vail, Bull. Torr. Bot. Club 24: 208. 1897. 

 Sparsely pubescent, diffusely branched from the base; the stems brittle, 

 striate, 1-4 dm. long: leaflets 3-4 pairs, 6-15 mm. long, oval to oblong, ob- 

 lique at the base: sepals linear-lanceolate, falling before the fruit matures: 

 petals obovate, obtuse or retuse : fruit finely pubescent, on a peduncle 1-2 cm. 

 long. Tribulus maximus in part. Southern Colorado and New Mexico. 



COVILLEA Vail. CREOSOTE BUSH 



Evergreen heavy-scented shrubs, with nodose branches, opposite 2-foliolate 

 leaves, and solitary yellow flowers. Sepals 5, deciduous. Petals 5, clawed. 

 Disk 10-lobed. Stamens 10; the filaments winged below and with a bifid scale 

 on the inner side. Ovary 5-celled. Fruit globose, short-stipitate, separating 

 into 5 hairy 1-seeded carpels. Larrea. 



1. Covillea tridentata (DC.) Vail, Bull. Torr. Bot. Club 22: 229. 1895. 

 Diffusely branched, 12-30 dm. high, densely leafy, of a yellowish hue: leaves 

 nearly sessile, the thick resinous leaflets inequilateral, oblong, 6-12 mm. 

 long, with a broad attachment to the rachis, somewhat curved: sepals ovate, 

 obtuse, silky: petals bright yellow, 6-8 mm. long: fruit 5 mm. in diameter, 

 beaked by the slender style. Larrea mexicana. A shrub of the dry mesas; 

 southern Colorado to Texas and west to California. 



62. RUTACEAE Juss. RUE FAMILY 



Shrubs or small trees, with pellucid or glandular-dotted aromatic leaves, 

 definite hypogynous stamens, and few seeds. Sepals and petals 4 or 5, imbri- 

 cated in the bud. Stamens as many or twice as many as the petals, inserted 

 outside of a hypogynous disk. Stipules none. 



Leaves 3-foliolate 1. Ptelea. 



Leaves simple 2. Thamnosma. 



1. PTELEA L. HOP TREE. . SHRUBBY TREFOIL 



Shrubs or small trees, with trifoliolate leaves, and small, polygamous, 

 greenish-white flowers in terminal cymes or compound umbels. Stamens 4 or 

 5. Ovary with a short thick stipe, 2-celled ; the cells 2-ovuled, the lower ovule 

 abortive. Fruit orbicular, broadly winged. 



1. Ptelea crenulata Greene, Pitt. 1: 216. 1888. A shrub or small tree 

 2-7 m. high, glabrous except the tomentulose flowers: leaflets ovate-lanceolate 



