246 ASTER ORDER 



(r) Scales of the pappus 10-20 HYMENOPAPPUS 

 (s) Scales of the pappus 4-14 CHAENACTIS 

 b. Heads green or greenish-yellow, inconspicuous 



(1) Leaves not lobed or divided 



(a) Leaves opposite IVA 



(b) Leaves alternate 



x. Fruit a spiny bur with 2 achenes XANTHIUM 



y. Achenes not in a bur 

 (x) Receptacle chaffy 



m. Pappus of several scales DICORIA 



n. Pappus none PARTHENICE 



(y) Receptacle without chaff; pappus 



none ARTEMISIA 



(2) Leaves lobed to pinnatifid 



(a) Some of the leaves opposite; spines of 



fruit in 1 row AMBROSIA 



(b) Leaves regularly alternate 



x. Spines of fruit in several rows FRANSERIA 



y. Achenes not in a spiny fruit 



(x) Bracts imbricated, not sharp-pointed ARTEMISIA 

 (y) Bracts in one row, sharp-pointed OXYTENIA 

 2. Heads with rays 



a. Receptacle with chaffy scales among the disk- 

 flowers 



(1) Rays not yellow 



(a) Rays white 



x. Leaves finely dissected 



(x) Rays 2-6 ACHILLEA 



(y) Rays 10-18 ANTHEMIS 



y. Leaves entire to pinnatifid 



(x) Rays 4-9; pappus none MELAMPODIUM 



(y) Rays 8-13 ; pappus hairy LAYIA 



z. Leaves 2-3-pinnatifid into linear seg- 

 ments; involucre white-bordered LEUCAMPYX 



(b) Rays pink to purple ; chaff spiny BRAUNERIA 



(2) Rays yellow 



(a) Rays pistillate, i. e., with a style 

 x. Achene broadly winged; pappus of 2 



awns XIMENESIA 



y. Achene scarcely or not at all winged 

 (x) Rays 2-5 



