Slimleaf Bur Ragweed

Ambrosia longistylis Nutt. Trans. Am. Phil. Soc. II. 7: 344
1840.
Ambrosia artemisiifolia octocornis Kuntze, Rev. Gen. 305. 1891.
An annual herb, with branched roots; stem 2-3 dm. high, scabrous-hispidulous, the hairs
with pustulate bases; leaves pinnately divided, 3-7 cm. long, scabrous-hispidulous as the stem,
dark-green, strongly ribbed; petioles 1-2 cm. long, often wing-margined, hispidulous; blades
ovate in outline; lobes oblong, mostly entire; staminate heads in a terminal raceme; involucre
4-5 mm. broad, 5-lobed, with broadly triangular acutish lobes, hispidulous, the hairs with
strongly pustulate bases; paleae of the receptacle filiform; pistillate heads usually many in
small clusters in the upper axils; style described as being an inch long, but in the type only
about 5 mm. long; body of the fruit obovoid, 3 mm. long, hispidulous, variegated; beak about
2 mm. long; spines 6-8, subulate, 0.6-0.7 mm. long, erect.
Type locality: "Rocky Mountains." Distribution: Western Nebraska and Wyoming.

Franseria tenuifolia* Harv. & Gray; A. Gray, Mem. Am. Acad
4: 80. 1849.
Ambrosia longistylis? A. Gray, Men. Am. Acad. 4: 79. 1849. Not A. longistylis Nutt. 1840. Franseria tenuifolia tripinnatifida A. Gray, Bost. Jour. Nat. Hist. 6: 227. 1850. Xanthidium tenuifolium Delpino, Studi. Lign. Anem. 62. 1871. Gaertneria tenuifolia Kuntze, Rev. Gen. 339. 1891.
A perennial herb; stem 3-6 dm. high, more or less hirsute with white spreading hairs; leaves interruptedly bior tripinnatifid, coarsely strigose on both sides and hirsute on the veins beneath, 1-1.5 dm. long; blades ovate in outline; segments of the lower leaves oblong or oval, obtuse or rounded at the apex, the terminal one short; segments of the upper leaves narrower, usually linear and acute, and the terminal one often elongate; inflorescence a leafy panicle but branches rather few; staminate heads many, on peduncles about 2 mm. long, nodding; involucre 3-4 mm. broad, turbinate-saucer-shaped, hispidulous and glandularpuberulent; lobes about 10, triangular; paleae of the receptacle filiform with slightly spatulate tips; corolla puberulent; pistillate heads in small clusters in the upper axils, 1-flowered, subtended by oval bract-like leaves; fruit hirsute and glandular-puberulent, reticulate, about 3 cm. long; beak solitary, conic; spines about 15 in 2-3 series, short, broadened at the base and hooked at the apex.
Type locality: Pofii Creek, between Bent's Fort [Colorado] and Santa Fe [New Mexico]. Distribution: Texas to California & Coahuila.

Ambrosia tenuifolia Spreng. Syst. 3: 851. 1826 An annual; stem 3-6 dm. high, terete, striate, hirsute; leaves bipinnatifid, hirsute-canescent with ascending hairs; petioles short; blades ovate or lance-ovate in outline; divisions narrowly linear, acute; staminate heads numerous in terminal racemes; involucre broadly obconic, hispidulous, crenate, 2.5 mm. broad; paleae of the receptacle filiform, as long as the corollas; corolla puberulent; pistillate heads in the upper axils, mostly solitary; body 2-2.5 mm. long, obovoid, hispidulous; beak more than 1 mm. long; tubercles 4 or 5, conic, more or less spreading, 0.5 mm. long.
Type locality: Montevideo, Uruguay.
Distribution: Adventive or naturalized in Louisiana and Porto Rico, and in France; native of Argentina and Uruguay.