STANDLEY TREES AND SHRUBS OF MEXICO IgU 



Leaves oval to elliptic or oblong, usually obtuse or rounded. 



Leaves oblong or elliptic-oblong 6. P. oblongum. 



Leaves oval or elliptic. 



Phyllaries acuminate 7. p. ervendbergii. 



Phyllaries obtuse to acute 8. P. punctatum! 



Leaves linear-filiform to lanceolate or rarely oblanceolate or ovate-lanceolate* 

 sessile or sometimes gradually narrowed at base into a short, usually mar- 

 gined petiole. 



Leaves 3 or 5-dentate 25. P. tridentatum. 



Leaves entire. 



Leaves ovate-lanceolate, semiamplexicaul, fleshy 21. P. amplexicaule. 



Leaves not amplexicaul. 



Leaves oblanceolate or linear-lanceolate to linear, usually over 2 mm. 

 wide, not terete. 

 Involucre green; heads short-peduncled, in close cymes. 

 Corollas whitish. 



Lower leaves lanceolate 9. P. brachypodum. 



Leaves narrowly lance-linear 10. P. pausodynum. 



Corollas ochroleucous. 



Heads 5 to 7-flowered; leaves narrowly linear. _ 11. P. confertum. 

 Heads about 15-flowered; leaves linear-oblanceolate. 



12. P. ochroleucum. 

 Involucre purple. 



Plants diffuse; heads nodding 13. P. cedrense. 



Plants erect; heads verj' rarely nodding. 



Corollas ochroleucous 14. P. obtusif olium. 



Corollas purplish. 



Leaves linear 15. P. linaria. 



Leaves narrowly linear-lanceolate to oblanceolate. 



16. P. seemannii. 

 Leaves linear-filiform or narrowly linear, rarely narrowly linear-elliptic, 

 usually terete and less than 2 mm. wide, more or less fleshy. 



Corollas purple 17. P. porf yreum. 



Corollas greenish yellow, ochroleucous, or whitish. 

 Phyllaries broadly oblong-oval or obovate. 



Leaves fihform, 2 to 4 cm. long; involucre 1 to 1.2 cm. high. 



23. P. greggii. 

 Leaves linear to elliptic, 2 cm. long or less; involucre 6 to 8 mm. 



high 24. P. crassifolium. 



Phyllaries linear or linear-oblong. 



Leaves very fleshy, about 2 mm. wide; plant very glaucous. 



20. P. raaritimum. 

 Leaves scarcely fleshy, 1 mm. wide or less; plants usually not 

 glaucous. 

 Achenes long-tapering at apex, about 8 mm. long. 



18. P. gracile. 

 Achenes not distinctlj' tapering at apex, 4 to 6 mm. long. 

 Tube of the corollas longer than the throat. 



19. P. pinif olium. 

 Tube of the corollas much shorter than the throat. 



22. P. scoparium. 



1. Porophyllum viridiflorum (H. B. K.) DC. Prodr. 5: 648. 1836. 

 Kleinia viridiflora H. B. K. Nov. Gen. & Sp. 4: 157. 1820. 

 Porophyllum lindenii Schultz Bip. in Seem. Bot. Voy. Herald 308. 1856. 



