Skeletonleaf Bur Ragweed

Perennials, 10–30+ cm. Stems erect. Leaves mostly alternate; petioles 8–25(–35+) mm; blades elliptic to lance-elliptic, 50–80(–180+) × 12–20(–50+) mm overall, (1–)2(–3)-pinnately lobed (lobes ± deltate), bases cuneate, ultimate margins with ± deltate teeth, abaxial faces densely finely scabrellous (silvery gray), adaxial faces strigillose. Pistillate heads clustered, proximal to staminates; florets (1–)2. Staminate heads: peduncles 2–9 mm; involucres saucer-shaped (with black nerves), 3–6+ mm diam., strigillose; florets 25–40+. Burs: bodies ± pyriform, somewhat flattened, 1.5–2.5(–4) mm, finely scabrellous, spines (1–)8–12+, scattered, stoutly conic, 0.5–1+ mm, tips straight.

Franseria discolor Nuttall; F. tomentosa (Nuttall) A. Nelson

Franseria discolor Nutt. Trans. Am. Phil. Soc. II. 7: 345
1840.
Ambrosia tomentosa Nutt. Gen. 2: 186. 1818. Not Franseria lomenlosa A. Gray, 1849.
Xanthidium discolor Delpino, Studi Lign. Anem. 63. 1871.
Gaertneria discolor Kuntze. Rev. Gen. 339. 1891.
Gaerlneria tomentosa A. Nelson, Bot. Gaz. 34: 34. 1902. Not G. tomentosa Kuntze, 1891.
A perennial herb, with a creeping rootstock; stem 2-4 dm. high, sparingly strigose; leaves interruptedly and irregularly bipinnatifid, elliptic in outline, white-tomentose beneath, strigose or glabrate above, 6-15 cm. long; petioles short; rachis winged, with small triangular segments interposed between the principal ones; ultimate divisions ovate or triangular, toothed; staminate heads in terminal racemes, the pistillate ones in the upper axils; involucre of the former green with dark veins, about 5 mm. in diameter, rotate, with about 10 short lobes; paleae of the receptacle hyaline, with a single purple vein, spatulate, shorter than the corolla; corolla with purple margins and angles; pistillate heads sessile, subtended by small bract-like elliptic or lanceolate leaves; fruit woody, strigose, about 6 mm. long, 2-celled; beaks 2, stout, conic, spreading, 2.5 mm. long, 1.5 mm. thick at the base, the upper lobe hooked; spines 8-12, in two or three series, subulate or conic, about 1 mm. long, thick and broadened at the base, scarcely hooked.
Type locality: (of F. discolor) Rocky Mountains near the Colorado of the West [Wyoming]; (of A. tomentosa) Upper Louisiana, on the banks of Missouri [South Dakota].
Distribution: Plains from South Dakota and Nebraska to New Mexico, Arizona, and Wvoming.

Ambrosia tomentosa, the skeletonleaf bur ragweed, silverleaf povertyweed, or skeleton-leaf bursage, is a North American species of perennial plants in the family Asteraceae.

Skeletonleaf bur ragweed is native to the west-central part of the United States, primarily the western Great Plains, the Colorado Plateau, and eastern Great Basin. It is often found growing alongside roads and in the sandy parts of plains.

It is considered a noxious weed in several states. It is also considered a severe allergen.