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FNA | Family List | FNA Vol. 21 | Asteraceae | Ambrosia

16. Ambrosia tomentosa Nuttall, Gen. N. Amer. Pl. 2: 186. 1818.

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

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.

Flowering Jun–Sep. Seasonally wet clays or sands, disturbed sites; (200–)1200–2100 m; Ariz., Colo., Idaho, Ill., Iowa, Kans., Mo., Mont., Nebr., N.Mex., N.Dak., S.Dak., Tex., Utah, Wis., Wyo.


 

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