156 
C0MP0S1TAE 
Ray-acbenes half enclosed by the bracts of the involucre 
which are rounded on the back, the bracts at 
length deciduous.14. Hemizonia,. 
Ray-achenes completely enfolded by the bracts of the 
involucre, which at base have thin margins and 
flattish backs. 
Achenes in fruit not expanding; pappus present or 
none ; flowers yellow, white, or yellow and 
white.15. Layia. 
Achenes in fruit expanding into a globose head; 
pappus silvery-scarious; flowers golden- 
yellow.16. Achyrachaena. 
Rays none; heads unisexual, small, greenish or white; pappus none; 
leaves alternate or the lowest opposite; fruit commonly a 
bur ; anthers distinct; styles as in Heliantheae; coarse weeds. 
Ambrosieae (Ragweed Tribe). 
Heads containing both staminate and pistillate flowers, the latter 
at the margin; involucre of 4 or 5 rounded united 
.bracts.17. Iva. 
Heads unisexual, both pistillate and staminate on the same plant; 
involucre of pistillate heads closed and bur-like, only the 
style-branches exserted; staminate heads in a raceme or 
spike, their involucres open. 
Involucral bracts of the staminate heads united; pistillate 
involucre beaked at apex and armed near the beak 
with a single row of short prickles. .. 18. Ambrosia. 
Involucral bracts of the staminate heads distinct; pistillate 
involucre maturing into a stout bur.. 19. Xanthium. 
Receptacle naked; bracts of involucre in 1, 2 or more series, little im¬ 
bricated ; flowers yellow; rays present; pappus of paleae, awns, 
bristles, or none.— Helenieae (Sneezeweed Tribe). 
Leaves opposite ; herbage glabrous or pubescent, never white-woolly. 
Bracts of the involucre distinct; pappus of paleae or bristles or 
both or none.20. Baeria. 
Bracts of the involucre united into a toothed cup. 
21. Lasthenia. 
Leaves alternate; herbage glabrous or white-woolly. 
Ray-corollas with a toothed appendage at base opposite the ligule ; 
pappus none ; leaves entire or denticulate ; annuals. 
22. Monolopia. 
Ray-corollas without appendage at base; pappus present; 
perennials. 
Bracts of the involucre erect; leaves divided or incised. 
23. Eriophyllum. 
Bracts of the .involucre reflexed; leaves not divided, often 
decurrent...24. Helenium. 
Involucral bracts scarious ; pappus none or reduced to a mere crown or ring ; 
flower white, yellow or greenish ; rays present or absent; leaves 
alternate, usually much divided ; strong-scented or aromatic plants.— 
Anthemideae (Mayweed Tribe). 
Receptacle with chaff-like bracts. 
Heads solitary, terminating leafy branches or peduncles; rays 14 to 
20; annual.25. Anthemis. 
Heads in a terminal corymb; rays 4 or 5 ; perennial....26. Achillea. 
Receptacle naked. 
Marginal flowers without a corolla ; heads discoid.27. Cotula. 
All of the flowers with a corolla; heads in panicled racemes or 
spikes, small.28. Artemisia. 
Pappus hair-like; bracts of the involucre little or not at all imbricated, in 1 or 
2 rows; receptacle naked; flowers yellow; leaves alternate or basal; 
pappus bristles soft, copious, mostly white; anthers not caudate.— 
Senecioneae (Groundsel Tribe). 
