Annual Ragweed

Ambrosia diversifolia (Piper) Rydberg, sp. nov
Ambrosia artemisiifolia diversifolia Piper, Contr. U. S. Nat. Herb. 11: 551. 1906.
An annual herb, with branched roots; stem about 5 dm. high, strigose-hirsute; lower leaves pinnately divided into oblong or lanceolate divisions, hirsutulous on both sides, somewhat paler beneath; petioles 1-2 cm. long; blades ovate in outline; upper leaves lanceolate or ovate, entire, subsessile, acute; staminate heads numerous, in racemes terminating the branches; involucre 5-6-lobed, 4-5 mm. broad, hispid-strigose; lobes broadly triangular, acute; paleae of the receptacle filiform; corolla puberulent; pistillate heads in few small clusters or solitary in the upper axils; body of the fruit obovoid, about 2.5 mm. long, hirsute-puberulent; beak fully 2 mm. long; spines 4-5, sharp, 0.5-0.8 mm. long.
Type locality: Gravelly banks of Alamota Creek at Alamota, Washington.
Distribution: Washington to Wyoming.

Ambrosia elatior L. Sp. PI. 987. 1753
Ambrosia elata Salisb. Prodr. 175. 1796.
Ambrosia artemisiifolia T. & G. Fl. N. Am. 2: 291, mainly. 1842. Not A. artemisiifolia L. 1753.
Ambrosia artemisiifolia quadricornis Kuntze, Rev. Gen. 305. 1891.
An annual herb, with branched roots; stem 3-10 dm. high, more or less hirsute or hispidulous, branched: leaves bipinnatifid or the upper less divided, hirsutulous-puberulent above, strigose beneath, and often hirsute on the veins; petioles 1-3 cm. long; leaf-blades ovate in outline; rachis winged, 1-3 mm. broad; segments lanceolate, acute, directed forward; staminate heads numerous, or in a predominately pistillate form few or none, in racemes terminating the branches; involucre slightly oblique, about 3 mm. wide, crenate, hirsutulous or hispidulous or in the western form long-hirsute, broadly obconic; paleae of the receptacle filiform ; corolla puberulent; pistillate heads in small clusters in the upper axils; body of the fruit obovoid, 3 mm. long, hispidulous-strigose, or in age almost glabrous, angled and somewhat reticulate; beak subulate, more than 1 mm. long; spines 5-7, subulate, short.
Type locality: Virginia.
Distribution: Nova Scotia to North Carolina, Arkansas, New Mexico, northern California, and Washington; Bermudas; also naturalized in Europe.