[From the Bulletin op lhe Torrey Botanical Club, 37: 127-148. 1910 ] 



Studies on the Rocky Mountain flora — XXI 



Per Axel Rydberg 



Ambrosia media sp. nov. 



Annual ; stem 4-6 dm. high, hispid with ascending or ap- 

 pressed short hairs, more or less strigose, branched; leaves pin- 

 nately divided, thick, 5-10 cm. long, scabrous and glandular- 

 granuliferous above, hispid-strigulose beneath, all except the 

 uppermost with shorter or longer, hirsute-ciliate, narrowly winged 

 petioles ; divisions oblong or lanceolate, usually more or less cleft 

 or toothed, the lobes or teeth lanceolate, acute; staminate racemes 

 rather dense ; involucre nodding, slightly lobed with 5 rounded 

 lobes and crenulate, 4-5 mm. in diameter, hispid- strigose ; hairs 

 about 0.5 mm. long, with more or less pustulate bases; receptacle 

 with few narrow lance-subulate scales ; fruit obovoid ; body about 

 3 mm. long, puberulent or in age glabrate, with 5-7 sharp spines 

 0.5 mm. long and strongly directed forward ; beak about 1 mm. 

 long, pubescent. 



In the form and texture of the foliage, this species resembles 

 A. coronopifolia T. & G. (A. psilostachya of most authors) as closely 

 as to make it almost impossible to distinguish the two by the leaves 

 alone, the only difference being that the leaves of A. media are 

 more inclined to be petioled and the petioles distinctly hispid- 

 ciliate. Otherwise, the plant is more closely related to A. elatior 

 and A. artemisiifolia, the root being annual and the fruit spiny. 

 A. coronopifolia has a larger fruit, which is inclined to be round- 

 elliptic instead of obovoid, is more pubescent, without spines, 

 either perfectly smooth or rarely with small rounded tubercles. 



Colorado : Fort Collins, Aug. 27, 1885, C. S. Q -andall (type, 

 in herb. N. Y. Bot. Gard.). 



New Mexico: Pecos, San Miguel County, Aug. 20, 1898, 

 Standley 5138 ; Kingston, 1904, Metcalfe 1337 (?). 



Coahuila : Saltillo 1898, Palmer 293. 



Montana : Sand Coulee, Sept. 7, 1885, R. S. Williams. 



Nebraska: Chadron, Oct. 9, 1897, /. M. Bates 706 (plants 

 predominantly pistillate). 



