4(3). Calyx silky-hairy, becoming much-inflated in fruit to increase the size 

 of the head 2 or 3 times 2. T. fragiferum. 



4. Calyx not as above (5) 



5(4). Flowers of head enclosed within 1 or 2 involucres; pod 1- or 2-seeded 

 3, T. pinetorum. 



5. Flowers of each floral circle of the heads enclosed within a separate involucre; 



3 to 6 involucres to the head; pod 2- to 6-seeded (6) 



6(5). Involucre coarsely toothed or 10- to 12-lobed with their lobes 3- to 6- 

 toothed 4. T. Wormskjoldii. 



6. Involucre with lobes not deeply cleft but 3- or 5-toothed (7) 



7(6). Heads 2-4 cm. wide; corolla 12 mm. or longer; standard emarginate at 

 apex 5. T. Fendleri. 



7. Heads 1-2 cm. wide; corolla less than 12 mm. long; standard obtuse and 



entire at apex 6. T. lacerum. 



8(2). Heads loose, few-flowered; involucre minute, rudimentary 7. T. nanum. 



8. Heads compact, turbinate, globose or hemispheric; involucre evident (9) 



9(8). Involucre glabrous, of 5 to 8 broadly obovate bracts at base of head and 

 an inner bract at the base of each flower 8. T. Parryi. 



9. Involucre densely pubescent, the several lobes triangular-linear and attenuate 



9. T. dasyphyllum. 



10(1). Perennial (doubtful cases should be keyed under both alternatives), with 

 densely plumose linear-attenuate calyx lobes (11) 



10. Annual or biennial (13) 



11(10). Heads mostly less than 2 cm. high; rare in extreme southeast Arizona 

 10. T. amabile. 



11. Heads rarely less than 2 cm. high; in eastern Arizona and/ or New Mexico 



(12) 



12(11). Stipules narrowly lanceolate, long-acuminate, glabrous; standard ovate- 

 lanceolate; pods glabrous, with 2 or 3 seeds 11. T. Rydbergii. 



12. Stipules ovate, abruptly short-acuminate, somewhat pubescent; standard 



elliptic; pods somewhat pubescent, with 2 seeds 



12. T. neurophyllum. 



13(10). Flowers sessile or subsessile in the heads; calyx more or less pubescent; 

 stipules oblong, conspicuously veined, the free portion triangular 

 with a setaceous point 13. T. pratense. 



13. Flowers conspicuously pedicellate in the long-peduncled heads; calyx glabrous 



(14) 



14(13). Stem creeping, often rooting at nodes; leaflets obovate, usually with a 

 whitish crescent toward base, notched at apex 14. T. repens. 



14. Stem erect or ascending; leaflets oval or ovate, without a white spot, rounded 



at apex 15. T. hybridum. 



1. Trifolium microcephalum Pursh 



Sparsely to densely villous annual with prostrate to erect stems 1-7 dm. long; 

 stipules ovate to ovate-lanceolate, denticulate-serrulate, about one-half as long as 

 the leaflets; leaflets 3, obovate-oblanceolate, 1.5-2.5 cm. long; heads involucrate, 

 5-10 mm. long, 10- to 60-flowered; involucres villous, sometimes exceeding the 

 lower flowers, shallowly crateriform, with about 10 (6 to 12) nearly entire 

 acute cuspidate shallow lobes; flowers 4-5 (-7) mm. long; calyx usually either 

 hirsute or villous (rarely glabrous), the simple teeth setaceous and longer than 

 the tube; corolla white to pinkish; legume 2-3 mm. long, 1- or 2-seeded, usually 

 rupturing the calyx by maturity. 



1048 



