ASTERACEAE: AMBROSIAE 185 



1. Iva. 908. 



Heads in the axils of leaves or bracts. 



Perennials, leaves entire or nearly so. 1. |. axillaris. 



Annuals, leaves coarsely serrate. 2. I. ciliata. 



Heads not in the axils of leaves or bracts. 3. I. xanthifolia. 



1. Iva axillaris Pursh. 



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. 



3. Iva xanthifolia (Fresen.) Nutt. 



In wet soil and waste places throughout the state. Bellevue; Lincoln; 

 Nebraska City; Plainview; Meadvllle; Red Cloud; Thedford; Whit- 

 man; Valentine. 



2. Ambrosia. 910. 



Leaves palmately 3-5 lobed or undivided, all opposite. 



Leaves 3-5 lobed. 1. A. trifida. 



Leaves not lobed. 1a. A. trifida var. integrifolia. 



Leaves 1-2-pinnatifid, the upper alternate. 



Annuals; fruiting involucre ending in a beak surmounted by 4-6 



spines. 2. Afl artemisiaefolia. 



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. 



A common weed in moist soil over most of the state. Holt County; 



Lincoln; Nebraska City; Wahoo; Wymore. 



la.. Ambrosia trifida var, intergrifolia (^luhl.) T. & G. 



Cody's Lakes; Lincoln; Nebraska City; Wahoo. 



2. Ambrosia artemisiaefolia L. Ragweed. 

 Common as a weed in dry soil throughout the state. Long Pine; Min- 

 den; Valentine. 



3. Ambrosia psilostachya DC. Ragweed. 

 A common weed in dry soil all over the state. Often abundant in dry 

 pastures. Alliance; Dismal River; Lincoln; Nebraska City; Valentine; 

 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. 



1. Gaertneria acanthicarpa (Hook.) Britton. 



In moist soil in the western part of the state. Crawford; Merriman; 



Porter. 



