GENUS 2. 



RAGWEED FAMILY. 



i. Ambrosia bidentata Michx. Lance- 

 leaved Ragweed. Fig. 4125. 



Ambrosia bidentata Michx. Fl. Bor. Am. 2 : 182. 1803. 



Annual, hirsute, usually much branched, very 

 leafy, i-3 high. Leaves lanceolate, mainly 

 alternate, sessile and somewhat cordate-clasping 

 at the base, acuminate at the apex, i-nerved, i'-3' 

 long, 2"-4" wide, usually with i or 2 sharp lobes 

 at the base and a few minute sharp teeth above, 

 or the upper ones quite entire, rough and hirsute 

 or ciliate; spikes of staminate heads dense, $'-7' 

 long, their involucres turbinate, bearing a long 

 lanceolate hispid reflexed lobe appearing like a 

 bract on the inner border, their receptacles chaffy ; 

 fertile heads solitary, or clustered, oblong, 

 4-angled, 3"-4" long, bearing 4 sharp spines. 



Prairies, Illinois to Missouri, Kansas, Louisiana 

 and Texas. July-Sept. 



2. Ambrosia trifida L. Horse-cane. Bitter- 

 weed. Great Ragweed. Fig. 4126. 



Ambrosia trifida L. Sp. PI. 987. 1753. 

 A. integrifolia Muhl. ; Willd. Sp. PI. 4: 375. 1805. 

 Ambrosia trifida integrifolia T. & G. Fl. N. A. 2 : 290. 

 1841. 



Annual, scabrous or hispid, or nearly glabrous, 

 branched, 3-i7 high. Leaves all opposite, petioled, 

 3-nerved, deeply 3-5-lobed, or undivided, the lobes 

 lanceolate or ovate, serrate, acute or acuminate; 

 lower leaves often i wide; racemes of sterile heads 

 3'-io' long, their involucres saucer-shaped, 3-ribbed 

 on the outer side, crenate-margined or truncate, their 

 receptacles naked; fertile heads usually clustered in 

 the axils of the upper bract-like leaves, turbinate to 

 obovoid, S-7-ribbed, conic-beaked, 3"-4" long, each 

 rib bearing a tubercle near the summit. 



In moist soil, Quebec to Florida, west to Manitoba, 

 Nebraska, Colorado and New Mexico. Tall ambrosia. 

 Richweed. Wild hemp. Horse-weed. Buffalo-weed. Hay-fever weed. July-Oct. 



3. Ambrosia elatior L. Ragweed. Roman 



Wormwood. Hogweed. Wild Tansy. 



Fig. 4127. 



Ambrosia elatior L. Sp. PI. 987. 1753. 

 Ambrosia artemisiaefolia L. Sp. PI. 988. 1753. 



Annual, pubescent, puberulent or hirsute, panicu- 

 lately branched, i-6 high. Leaves thin, i-2-pin- 

 natifid, petioled, 2'-4' long, the upper alternate, the 

 lower mostly opposite, pale or canescent beneath, 

 the lobes oblong or lanceolate, obtuse or acute ; 

 uppermost leaves of the branches sometimes linear- 

 lanceolate and entire ; racemes of sterile heads very 

 numerous, i'-6' long, the involucres hemispheric, 

 crenate, the receptacle chaffy ; fertile heads obovoid 

 or subglobose, mostly clustered, ii"-2" long, short- 

 beaked, 4-6-spined near the summit, sparingly pu- 

 bescent. 



In dry soil, often a pernicious weed in cultivated 

 fields, Nova Scotia to Florida, west to British Colum- 

 bia and Mexico. Bermuda. Introduced into Europe as a 

 weed. Consists of several slightly differing races. Also 

 called bitterweed, stickweed, stammerwort, carrot-weed, 

 black, or tassel-weed, hay-fever weed. July-Oct. 



