STANDLEY TREES AND SHRUBS OF MEXICO 1549 



Heads cymose or cymose-panicled at tips of stem and branches, rarely 

 solitary and very short-peduncled. 

 Leaves linear or linear-elliptic, 1.2 to 2.4 cm. long, 2 to 4 mm. wide 



16. P. microphyllum. 

 Leaves lanceolate or ovate, much larger. 



Phyllaries (at least the inner) acute or acuminate. 

 Leaves lanceolate or lance-oblong, cuneate at base. 



Leaves very scabrous on both sides 23. P. chalarolepis. 



Leaves smooth or nearly so above, slightly scabrous beneath. 



24. P. ghiesbreghtii. 

 Leaves ovate or lance-ovate. 



Heads few, 3 to 5 at apex of branches, long-pediceled. 



7. P. cornutum. 

 Heads usually numerous, cymose or cymose-panicled. 



Involilcre 2.5 to 3 mm. high 10. P. globosum. 



Involucre 4 mm. high or more. 



Phyllaries coarsely villous; leaves villous beneath. 



12. P. asperifolium. 

 Phyllaries not villous; leaves harshly pubescent beneath. 

 Leaves acutely cuneate at base, usually oblong-ovate or 



lance-ovate 15. P. purpusii. 



Leaves cuneate-rounded to truncate at base, mostly ovate. 



Phyllaries mostly acuminate 11. P. verbesinoides. 



Phyllaries acutish. 



Involucre bearing a few shining glands. 



17. P. goldmanii. 

 Involucre without shining glands. 

 Leaves less than 5 cm. long. 



Rays much longer than the disk 8. P. rude. 



Rays equaling the disk 18. P. pinetorum. 



Leaves 6 to 11 cm. long 9. P. pringlei. 



Phyllaries obtuse or rounded. 

 Leaves distinctly lanceolate. 



Stem simple; leaves strigillose beneath. 



19. P. rotundisquamum. 

 Stem branched; leaves antrorse-hispidulous or spreading-hispidu- 



lous beneath 20. P. lancifolium. 



Leaves ovate or lance-ovate. 



Heads very small, the involucre in anthesis 3 mm. thick. 

 Leaves 3 cm. long or less; pedicels 7 to 16 mm. long. 



21. P. microcephalum. 

 Leaves up to 10 cm. long; pedicels 1.2 to 2.5 cm. long. 



22. P. gracile. 

 Heads larger, the disk in anthesis 4 mm. thick or more. 



Phyllaries bearing a few shining glands 17. P. goldmanii. 



Phyllaries without glands. 

 Petioles 1 cm. long or more. 



Leaves usually rounded at base, ovate 9. P. pringlei. 



Leaves acutely cuneate at base, usually oblong-ovate or 



lance-ovate 15. P. purpusii. 



Petioles much less than 1 cm. long. 



Leaves refiexed, conduplicate, with crisped margins. 



4. P. chihuahuense. 

 Leaves not refiexed, plane. 



Leaves cordate-ovate, small, 1.5 to 3 cm. long. 



6. P. subcordatum. 



