LOCAL FIELD CHARACTERS: Annual bursage is the only annual 

 species in the genus with distinctly spiny fruits. 

 Perennial bursage ( Ambrosia tomentosa ) has spiny fruits but 

 it is a generally a smaller plant of 1-4 dm (3.1-12.4 in), 

 with leaves that are white pubescent beneath rather than 

 glabrous and green. Annual bursage may be difficult to 

 distiniguish vegetatively from first year plants of the 

 Western ragweed ( Ambrosia p silostachya ) which is perennial; 

 and from young plants of the Giant ragweed ( Ambrosia 

 trif ida ) which commonly grov/ 1-3 m (3-9 ft) tall. 



GEOGRAPHICAL DISTRIBUTION 



1. RANGE: Annual bursage is known from the Great Plains, v/est 

 to WAshington, California and Arizona. It has been 

 collected in the southwest, northcentral , and southeastern 

 areas of Montana (Dorn 1984) , representing half of the 

 regions of the state. 



2. CURRENT SITES: The only site where Annual bursage has been 

 collected in the past 40 years is from the Little Muddy 

 Creek in the Garfield County study area. 



3. HISTORICAL SITES: Five of the six collections made of this 

 species were collected before 1940. 



4. UNVERIFIED/UNDOCUMENTED REPORTS: There are a few other 

 similar sandy streambottom segments that have been reworked 

 by the wind into v;ell-developed sand dunes along Little 

 Muddy Creek in Garfield County, but these are not on BL.M 

 lands and v/ere not evaluated. 



5. AREAS SURVEYED BUT SPECIES NOT LOCATED: Suitably open sandy 

 habitat was not found elsewhere in the course of this 

 project. The only potential habitat for it suspected from 

 the area might be segments of sandy shore on the Fort Peck 

 Reservior . 



ASSOCIATED VEGETATION: Annual bursage colonizes loose sandy 

 settings as a pioneer species in prairie. Associated 

 species that were documented at the Little Muddy Creek site 

 in the study area include: Calamovilfa lonqifolia , Orvzopsis 

 hymenoides, Sporobolus cryptandrus and Chrysopsis villosa . 

 The vegetation there is very sparse, and annual bursage v.'as 

 often the most common plant in these settings. 



TOPOGRAPHY: This species occupies the toeslopes and gently^ 

 rolling margins of sand dunes. 



