GENUS 2. RAGWEED FAMILY. 
1. Ambrosia bidentata Michx. Lance- 
leaved Ragweed. Fig. 4125. 
Ambrosia bidentata Michx. Fl. Bor. Am. 2: 182. 1803. 
Annual, hirsute, usually much branched, very 
leafy, 1°-3° high. Leaves lanceolate, mainly 
alternate, sessile and somewhat cordate-clasping 
at the base, acuminate at the apex, I-nerved, 1’-3’ 
long, 2’’-4” wide, usually with 1 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, 3’-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. 
weed. Great Ragweed. Fig. 4126. 
Ambrosia trifida L. Sp. Pl. 987. 1753. 
A, integrifolia Muhl.; Willd. Sp. Pl. 4: 375. 1805. 
Ambrosia trifida integrifolia T. & G. Fl. N. A. 2: 290. 
1841. 
e 
Annual, scabrous or hispid, or nearly glabrous, 
branched, 3°-17° 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 1° wide; racemes of sterile heads 
3-10’ 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, 5-7-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. 
We 
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NP, 
3. Ambrosia elatior L. Ragweed. Roman 
Wormwood. Hogweed. Wild Tansy. 
Fig. 4127. 
Ambrosia elatior L. Sp. Pl. 987. 1753. 
Ambrosia artemisiaefolia L. Sp. Pl. 988. 1753. 
Annual, pubescent, puberulent or hirsute, panicu- 
lately branched, 1°-6° high. Leaves. thin, 1-2-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, 1’-6’ long, the involucres hemispheric, 
crenate, the receptacle chaffy; fertile heads obovoid 
or subglobose, mostly clustered, 13’-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. 
