1564 CONTRIBUTIONS FROM THE NATIONAL, HERBARIUM 



Leaves opposite, toothed. 



Involucre several-seriate 18. Z. lantanifolia. 



Involucre 2-seriate 22. Z. strigosa. 



Leaves large, mostly 10 cm. long or more. 



Leaves densely and rather softly appressed- or incurved-pilose beneath. 

 Awns continuous with the very narrow, winglike margins of the aehene; 



phyllaries mostly oblong 3. Z. crocea. 



Awns not continuous with the margins of the aehene; phyllaries 



lanceolate 22, Z. strigosa. 



Leaves sparsely and harshly strigillose, hispidulous, or hirsute beneath. 

 Outer phyllaries mostly oval or suborbicular, rounded or rarely acutish 



at apex 1. Z. ghiesbreghtii. 



Outer phyllaries ovate, usually acuminate 2. Z. greggii. 



Heads usually numerous in umbelliform cymes, or panicled, if sometimes ternate 

 then on pedicels less than 5 cm. long (rarely up to 5.8 cm. in no. 7). 

 Leaves elliptic or elliptic-oblong, 1.5 cm. wide or less, strongly 3-nerved. 



17. Z. seemannii. 

 Leaves ovate or lance-ovate, usually wider, tripUnerved. 

 Petioles very short, 3 mm. long or less. 



Branches hirsute-pilose with loosely spreading hairs; leaves shallowly 



cordate at base 16. Z. cordifolia. 



Branches strigose or strigillose; leaves rounded at base. 



Heads 1 to 5, the pedicels mostly 2 to 5.8 cm. long 7. Z. fruticosa. 



Heads numerous, the pedicels 1 to 2 cm. long 15. Z. microcephala. 



Petioles of the main leaves more than 5 mm. long. 



Heads numerous in close terminal umbelliform cymes or cymose panicles. 

 Heads larger, the disk in anthesis 7 to 10 mm. thick. 



Pedicels usually 2 cm. long or less; petioles 1 cm. long or less. 



5. Z. michoacana. 

 Pedicels usually over 2 cm. long; petioles 1 to 3.5 cm. long. 



8. Z. frutescens. 

 Heads smaller, the disk in anthesis usually less than 5 mm. thick. 

 Phyllaries (at least the outer) acuminate or subacuminate, the tips 

 usually spreading. 

 Involucre 9 to 10.5 mm. high; pedicels densely spreading-hirsute, 



1.4 cm. long or less 9. Z. aggregata. 



Involucre 9 mm. high or less; pedicels strigose or strigillose, usually 

 2 to 5 cm. long. 



Involucre 7 to 9 mm. high; heads 3 to 6 10. Z. gracilis. 



Involucre 6 mm. high or less; heads usually more numerous. 



11. Z. fasciculata. 

 Phyllaries obtuse to broadly rounded (the outermost sometimes 

 acute or acutish), the tips appressed. 

 Phyllaries (except the two outermost) all with very broadly rounded 



tips 14. Z. rotundata. 



Phyllaries obtuse or rarely acutish. 



Awns longer than the body of the disk achenes, conspicuously 



exserted in the fruiting heads 12. Z. ceanothifolia. 



Awns shorter than the body of the disk achenes, not exserted in 



fruit 13, Z, gradata. 



Heads several or numerous and loosely panicled, or in terminal cymes of 



3 to 5, not numerous and umbelled. 



Involucre 8 to 15 mm. high, the outermost phyllaries with ovate base 



and abruptly narrower, equal or longer, spreading, herbaceous 



tips 24, Z, leucactis. 



