Colorado Weed Seeds 
71 
2. Ragweed, Bitter-weed, Roman Wormwood 
(Ambrosia (Tourn.) L.) 
Fruit enclosed in a nut-like involucre bearing 6, or rarely 7, stout projec- 
tions or spines, usually 5 short spines and 1 long, central spine at the top, 
and the others just below the top or summit. 
Key to Species 
Seeds 2-3.5 mm. long \..A. artemisaefolia 
Seeds 5-10 mm. long 2.. A. trifida 
Fig. 136. Great Ragweed 
(Ambrosia trifida). x 12 
2. Ragweed, Roman Wormwood, 
Hog- WEED (Ambrosia artemisaefolia A. 
Gray, Ambrosia elatior L.) (Fig. 
187). — Seeds neutral-gray to dark 
olive-gray in color, 5-7 ridged, either 
distinct or obscure, the ridges termin- 
ating in spines near the summit of the 
seed which itself tapers off into a 
spine or projection ; seeds 2-3.5 mm. 
long, broad at the apex, narrower at 
the base. 
1. Great Ragweed, Kinghead 
(Ambt'osia trifida L.) (Fig. 136). — 
Seeds white, cream-buff or honey- 
yellow in. color, distinctly 5-6 ridged, 
the ridges ending in stout projec- 
tions or spines near the summit ; 
the apex of the seed terminates in 
a single stout projection which 
appears distinctly above the other 
spines ; seeds variable in size usually 
5-8 mm. long but occasionally 1- cm. 
long, broad at the top, narrow at 
the base. 
Fig. 137. Ragweed 
(Ambrosia artemisaefolia 
a. Involucre enclosing 
achene. b. Achene. x 11. 
3. Marsh Elder, Salt Sage, Bozzleweed 
(Iva L.) 
Achenes compressed, mostly roughened, dull, marginless, pear-shaped, 
sides slightly concave; pappus absent. 
