Studies on the Rocky Mountain flora— XxXI 
Per AXEL RYDBERG 
* Ambrosia media sp. nov. 
nnual; 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. e/atior 
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. 
Cotorapo: Fort Collins, Aug. 27, 1885, C. S. Crandall (type, 
in herb. N. Y. Bot. Gard.). 
New Mexico: Pecos, San Miguel County, Aug. 20, 1898, 
Standley 5138 ; Kingston, 1904, Metcalfe 1337 (?). 
Coaunuita: Saltillo 1898, Palmer 293. 
Montana: Sand Coulee, Sept. 7, 1885, &. S. Williams. 
Nepraska: Chadron, Oct. 9, 1897, /. M@. Bates 706 (plants 
predominantly pistillate). 
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