266 



COMPOSITAE. 



Machaeranthera canescens viscosa (Nutt.) Piper. Biennial, erect, much 

 branched above, and simple or branching at the base, 30-60 cm. high, whitish- 

 puberulent throughout; leaves rigid, linear-lanceolate or the lower spatulate, 

 cuspidately-toothed or entire, 2-6 cm. long, those of the flowering branches 

 much reduced; heads usually numerous, paniculate or corymbosely arranged; 

 involucre turbinate-campanulate, 10-15 mm. broad, the bracts in numerous 

 imbricated ranks, the tips green, very glandular on the upper side, at length 

 spreading or recurved; rays purple or violet, 8-10 mm. long; akenes canescent; 

 pappus sordid. Dry soil, often abundant and becoming a weed. 



401. ERIGERON. Fleabane. 



Herbs ; very similar to Aster, but differing in the usually naked- 

 peduncled heads; involucre simpler, of narrow and erect equal 

 bracts, not coriaceous and without herbaceous tips; rays narrower 

 and usually very numerous, often in more than one row; pappus 

 more scanty or fragile, sometimes with a conspicuous short outer 

 row ; style appendages very short and roundish or obtuse ; akenes 

 mostly 2-nerved. 



Rays very short or wanting. 



Plant low; head solitary. E. bloomeri. 



Plants tall; heads several to many. 



Rays wanting; leaves firm; root perennial. E. inornatus. 



Rays present, very short; root annual or biennial. 



Annual; heads panicled; involucre glabrous. E. canadensis. 



Biennial; heads corymbose; involucre hairy. E. acris. 



Rays conspicuous, much surpassing the disk. 

 Roots annual or biennial, fibrous. 



Stems diffusely branched; rays white or violet. E. divergens. 



Stems erect, branched above; rays white. E. ramosus. 



Roots stout; plants perennial. 



Tall species with flat, rather broad and large leaves. 



Involucre viscid; rays 30-50, broad. E. membranaceus. 



Involucre smooth or hirsute; rays 100-150, 

 narrow. 

 Leaves entire; ray flowers violet. E. speciosus. 



Leaves dentate; ray flowers pink. E. philadelphicus. 



Low species; leaves narrow. 



Rays yellow; leaves linear, entire. E. filifolius. 



Rays not yellow. 



Leaves parted into linear lobes. E. compositus. 



Leaves entire, narrow. 



Stems simple, scapiform; head always 



solitary. E. poliospermus. 



Stems branched, leafy, usually bearing 

 several heads. 

 Pubescence long and dense. E. hispidissimus. 



Pubescence short. 



Radical leaves linear-lanceolate, 



3-nerved. E. corymbosus. 



Radical leaves filiform or linear, 



1-nerved. E. linearis. 



Erigeron bloomeri Gray. Perennial, densely tufted, from a woody base; 

 pubescence fine and appressed; basal leaves spatulate-linear, 2-6 cm. long, 



