190 Order CAMPANULALES 
Pistillate involucre 1-flowered, usually armed with 4-8 tubercles 
or spines in a single series. 2. Ambrosia. 
Pistillate involucre with 1-4 flowers, armed with several to 
numerous prickles in more than one series. 3. Gaertneria. 
Involucre of the staminate heads of separate bracts; that of the 
pistillate heads 2-flowered, covered with numerous hooked 
bristles. 4. Xanthium. 
1. Iva. 908. 
Heads in the axils of leaves or bracts. 
Perennials; leaves entire or nearly so. 1. I. axillaris. 
Annuals; leaves coarsely serrate. 2. I. ciliata. 
Heads not in the axils of leaves or bracts. 3. I. xanthiifolia. 
1. Iva axillaris Pursh. Marsh-elder. 
In alkaline soil in the western part of the state. Scotts Bluff 
county. 
2. Iva ciliata Willd. 
In moist soil in waste places in the southeastern part of the state. 
Lincoln; Minden; Red Cloud; Republican City. 
3. Iva xanthiifolia (Fresen.) Nutt. 
In wet soil and waste places throughout the state. Bellevue; Lin- 
coln; Meadville; Nebraska City; Plainview; Red Cloud; Thedford; 
Valentine; Whitman. 
2. Ambrosia. 910. 
Leaves palmately 3—-5-lobed or undivided, all opposite. 1. A. trifida. 
Leaves 1-2-pinnatifid, the upper alternate. 
Annuals; fruiting involucre ending in a beak surrounded by 4-6 
spines. 2. A. elatior. 
Perennials by creeping root-stocks; fruiting involucre ending in a 
sharp point surrounded by about 4 tubercles or unarmed. 
3. A. psilostachya. 
1. Ambrosia trifida L. Giant Ragweed. 
A common weed in moist soil over most of the state. Cody’s Lakes; 
noe county; Lincoln; Nebraska City; Wahoo; Wymore; Weeping 
ater. 
2. Ambrosia elatior L. Annual Ragweed. 
Ambrosia artemisizfolia L. 
Common as a weed in dry soil throughout the state. Long Pine; 
Minden; Valentine; Weeping Water. 
3. Ambrosia psilostachya DC. Western Ragweed. 
A common weed in dry soil all over the state. Often abundant in 
dry pastures. Alliance; Dismal River; Lincoln; Nebraska City; 
Valentine; Weeping Water; Whitman. 
3. Gaertneria. 911. 
Leaves not densely white-tomentose beneath; annuals. 
1. G. acanthicarpa. 
Leaves densely white-tomentose beneath; perennials. 
Leaves bipinnatifid, terminal segment not larger than the lateral. 
2. G. discolor. 
Leaves pinnately divided, terminal segment much larger than the 
lateral. 3. G. tomentosa. 
