ASTER FAMILY 249 



n. Receptacle without bristles 



(m) Leaves alternate or basal, usu- 

 ally without glands 

 r. Involucral scales spreading or 



reflexed; stems 2-6 ft. high HELENIUM 

 s. Involucral scales not spread- 

 ing or reflexed; stems less 

 than 2 ft. high as a rule 

 (r) Involucre densely woolly; 



leaves parted or divided ; ^ 



alpine RYDBERGIA 



(s) Involucre not densely wool- 

 ly ; leaves entire or if di- 

 vided, not alpine ACTINELLA 

 (n) Leaves usually opposite, with 



distinct oil-glands 



r. Leaves entire, narrow PECTIS 



s. Leaves divided DYSODIA 



(z) Achenes flattened, roundish or 



swollen, sometimes striate 

 m. Heads small, disk-flowers 1-12 ; 



rays 1-10 



(m) Rays 2-3-lobed, 4-15 mm. long PSILOSTROPHE 

 (n) Rays not lobed, 1-2 mm. long GUTIERRETZIA 

 n. Heads large, disk- and ray-flowers 



many; involucres gummy GRINDELIA 



(b) Rays white to purple 

 x. Marginal flowers not true rays, merely 



ray-like CHAENACTIS 



y. Marginal flowers true rays 



(x) Rays rose-purple POLYPTERIS 



(y) Rays white CHRYSANTHEMUM 



3. Heads with all the flowers ray-like or strap- 

 shaped, the central sometimes imperfect and 

 closed; typically with milky juice 



a. Pappus of blunt scales ; flowers blue CICHORIUM 



b. Pappus of plumy, hair-like bristles or bristle- 



like scales 



(1) Achenes with a beak, bristles interwoven TRAGOPOGON 



(2) Achenes not beaked 



(a) Flowers pink; pappus plumy PTILONIA 



