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.
