AMBROSIACEAE (RAGWEED FAMILY) 



2 a Flowers orange or orange-red 



ORANGE HAWKWEED. (H. aurantlacum.) 

 b Flowers yellow 3 



3 a Flowering stem with i head ; head i in. or more broad 



MOUSE-EAR HAWKWEED. (H. pilosella.) 

 b Flowering stem with more than i head; heads %-% 



in. broad RATTLESNAKE-WEED. (H. venbsum.) 



4 a A tuft of basal leaves present at flowering time 5 



b No tuft of basal leaves present at flowering time 6 



5 a Basal leaves obovate to oblong, usually with glandular 



teeth; achenes oblong 



MARYLAND HAWKWEED. (H. marianum.) 

 b Basal leaves ovate to obovate, entire; achenes spindle- 

 shaped; stem covered with long hairs at the base 



GRONOVIUS' HAWKWEED. (H. gronbvii.) 



6 a Plant very hairy, with glandular hairs above 



ROUGH HAWKWEED. (H. scabrum.) 

 b Plants not noticeably hairy 7 



7 a Leaves coarsely toothed especially below the middle; 



principal bracts of involucre in 2 or 3 rows 



CANADA HAWKWEED. (H. canadense.) 

 b Leaves remotely toothed ; principal bracts of involucre 



in i row PANICLED HAWKWEED. (H. paniculatum.) 



12 NABULUS. 



1 a Bracts of involucre very hairy; flowers purplish 



GLAUCOUS WHITE LETTUCE. (N. racembsus.) 

 b Bracts of involucre not hairy, or with few scattered 



hairs ; flowers rarely purplish 2 



2 a Heads 5-7-flowered ; principal bracts of involucre about 5 



TALL WHITE LETTUCE. (N. altissimus.) 

 b Heads 8-i5-flowered; principal bracts of involucre 6-10 3 



3 a Heads in a spike-like raceme, often i-sided ; plant not 



branched. .. .SLENDER RATTLESNAKE-ROOT. (N. virgatus.) 

 b Heads in a panicle; plants more or less branched above 4 



4 a Pappus reddish-brown RATTLESNAKE-ROOT. (N. dlbus.) 



b Pappus light-brown or straw-colored 5 



5 a Small outer bracts of involucre lanceolate; branches of 



panicle widely spreading. .LION'S-FOOT. (N. serpentarius.) 

 b Small outer bracts of involucre ovate to triangular; 

 branches of panicle ascending 



TALL RATTLESNAKE-ROOT. (N. trifoliatus.) 



5 AMBROSIACEAE. Ragweed Family. 

 i AMBR6SIA. 

 i a Leaves pinnatifid, the segments lobed or coarsely toothed 



COMMON RAGWEED. (A. artemisiaefblia.) 

 b Leaves 3~5-lobed, the lobes toothed 



GREAT RAGWEED. (A. trifida.) 



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