FLOWERING PLANTS AND FERNS OF ARIZONA 423 



or panicles, or solitary in the leaf axils, the petals yellow; stamens 5 

 or 10, often unequal, some of them sometimes sterile; pods dehiscent 

 or indehiscent, flat or turgid, the walls thin, or thick and almost woody. 

 A very large genus, chiefly tropical and subtropical, of which a few 

 species are cultivated as ornamentals in the warmer parts of the 

 United States. The cathartic drug senna is obtained from certain 

 Old World species. 



Key to the species 



1. Pods indehiscent or tardily and not elastically dehiscent; stems usually 1 m. 



long or longer (2). 



2. Stipules none; leaflets fugacious, few and distant, less than 1 cm. long, 



thickish, oval or oblong-ovate; pods turgid, spinulose-tipped, not more 



than 4 cm. long; plant shrubby; rachis spinescent; petiole and rachis 



gland-bearing; flowers in loose terminal panicles 1. C. armata. 



2. Stipules present; leaflets persistent; pods compressed, linear, 6 cm. long or 

 longer (3). 

 3. Petiole not gland-bearing; plant a shrub, with rigid branches; leaflets 2 or 

 3 pairs, less than 1 cm. long, oval or obovate, often cuspidate, thickish, 

 glabrous or strigose, the veins usually thick and prominent beneath; 

 inflorescences few-flowered, axillary and terminal; pods up to 12 cm. 

 long, fiat, black and shiny at maturity, rigidly apiculate. 



2. C. WISLIZENI. 



3. Petiole bearing a large gland near the base; plant herbaceous or at most 

 suffrutescent, appearing glabrous but usually puberulent; leaflets 4 to 

 8 pairs, 2 cm. long or longer, lanceolate or oblong-lanceolate, sharply 

 acuminate, thin; inflorescences usually many-flowered, terminal; pods 

 up to 25 cm. long, compressed but not flat, brown and not shiny at 



maturity 3. C. leptocarpa. 



1. Pods more or less promptly and elastically dehiscent; plants herbaceous or 



barely suffrutescent; stems usually much less than 1 m. long (4). 



4. Rachis of the leaves normally eglandular; petals not conspicuously veined (5). 



5. Leaflets 2 pairs, 6 mm. wide, or wider, obovate or oval, thin, ciliate; 



petioles normally eglandular; petals nearly equal, about 5 mm. 



long; pods sparsely long-hirsute; seeds obovate, smooth, black and 



shining ; plant annual ; stems glandular-hirsute 4. C. absus. 



5. Leaflets 6 or more pairs, not more than 3 mm. wide, narrowly oblong or 



oblanceolate, mucronate or cuspidate; petioles bearing a cup-shaped, 



usually stipitate gland; petals conspicuously unequal; pods appressed- 



pubescent; seeds not black and shiny (6). 



6. Plant perennial; stems decumbent or prostrate, glabrous or nearly so; 



leaflets 6 to 9 pairs, glabrous; pedicels seldom less than 10 mm. long; 



longest petal not less than 12 mm. long; seeds obovate, smooth. 



5. C. WRIGHTII. 



6. Plant annual; stems erect or ascending, pubescent with short, subap- 

 pressed, and longer, spreading hairs; leaflets usually more than 9 

 pairs, long-ciliate; pedicels seldom more than 5 mm. long; longest 

 petal 5 to 7 mm. long; seeds irregularly triangular or quadrangular, 



rugose 6. C. leptadenia. 



4. Rachis usually bearing 1 or more subulate glands, these situated between the 

 opposite leaflets; petals conspicuously veined; leaflets oblong, elliptic, 

 or obovate, 6 mm. wide, or wider; plants perennial; pubescence of the 

 leaves, stems, and pods soft; seeds gray or olive brown, dull, rugose (7). 

 7. Leaflets one pair; flowers all axillary, solitary or in 2's on peduncles sur- 

 passing the petioles; pubescence all appressed or partly spreading; 



pods obliquely cuspidate 7. C. bauhinioides. 



7. Leaflets 2 or more pairs; flowers in terminal leafy panicles, as well as in 

 axillary clusters (8) . 

 8. Leaflets 2 or 3 pairs; pubescence closely appressed; anthers orange; pods 

 2 to 3 cm. long, with the cusp central, erect or nearly so, 2 to 4 mm. 



long 8. C. covesii. 



8. Leaflets 4 to 8 pairs; pubescence not closely appressed; anthers red; 

 pods 3.5 to 6 cm. long, with the cusp usually somewhat lateral and 

 ascending, 1 to 2 mm. long 9. C. lindheimeriaxa. 



