1548 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM 



Leaves ovate, less than 3 times as long as wide. 

 Phyllaries distinctlj* acute or acuminate. 



Ph^'llaries and under surface of leaves pilose-tomentose or villous. 



Leaves cordate at base, scabrous above 12. P. asperifolium^ 



Leaves cuneate or rounded-cuneate at base, scarcely- scabrous above. 



30. P. lasiolepis. 

 Phyllaries strigillose; leaves subcanescently strigose and strigillose or 

 hispidulous beneath. 

 Leaves slightly reticulate, strigose and strigillose or antrorse- 



hispidulous beneath 31. P. blepharolepis. 



Leaves densely reticulate and hispidulous with more or less spread- 

 ing hairs beneath 32. P. hypoleucum. 



Phjdlaries obtuse or rounded, or sometimes acuminately narrowed to an 

 obtuse apex. 

 Involucre 4 to 6.5 mm. high. 



Involucre 4 to 4.5 mm. high, 4.5 to 5 mm. thick. 



32. P. hypoleucum.. 

 Involucre 5.5 to 6.5 mm. high, 5 to 7 mm. thick. 



33. P. consobrinuni. 

 Involucre 7 to S mm. high. 



Pubescence of the lower leaf surface ochroleucous.. 34. P. coUinum. 

 Pubescence of the lower leaf surface bluish white. -35. P. ovatum. 

 Leaves green beneath as well as above. 



Heads large, the disk in anthesis 8 to 12 mm. thick. 

 Petioles 3 mm. long or less. 



Phyllaries with herbaceous tips 5. P. subsquarrosum. 



Phjdlaries without herbaceous tips 36. P. acuminatum. 



Petioles of the larger leaves 1 cm. long or more. 



Middle and inner phyllaries 5 mm. wide or more, broadly rounded. 



39. P. latisquamium. 

 Middle and inner phyllaries less than 5 mm. wide. 



Leaves hispidulous chiefly along the veins beneath; some of the phyl- 

 laries usually acute or acuminate 37. P. macrocephalum. 



Leaves rather densely pilosulous to subtomentose beneath; phyllaries 



all obtuse or rounded at apex 38. P. nelsonii. 



Heads smaller, the disk in anthesis 7 mm. thick or less. 



Leaves, branchlets, and involucres densely glandular. _ 13. P. glandulosum. 

 Leaves, branchlets, and involucres not densely glandular, the involucre 

 sometimes with a few glands. 

 Heads solitary and long-peduncled, or several and cymose at the tip of 

 an elongate, essentially naked peduncle. • 



Heads solitarj^ rarely 2 or 3, long-peduncled __1. P. buphthalmoides. 

 Heads several, cymose at the tips of elongate, essentially naked pe- 

 duncles. 

 Leaves (at least the middle and upper) entire, strongly conduplicate. 



2. P. jaliscense. 

 Leaves distinctly serrate or serrulate. 



Leaves conduplicate; phyllaries essentially without herbaceous 



tips 4. P. chihuahuense. 



Leaves plane, rarely somewhat conduplicate; phyllaries with 

 distinctly herbaceous tips. 

 Stem leaves smaller, elliptic to lanceolate, 1.8 cm. wide or less. 



3. P. parvifolium. 

 Stem leaves larger, ovate, 2 to 3.5 cm. wide. 



5. P. subsquarrosum. 



