12.
Ambrosia acanthicarpa
Hooker, Fl. Bor.-Amer. 1: 309. 1833.
Franseria acanthicarpa
(Hooker) Coville
Annuals,
10—80+ cm.
Stems
erect.
Leaves
opposite (proximal) and alternate; petioles 5—15(—25+) mm; blades ± deltate, 15—40(—85+) × 12—35(—80+) mm, 1—2-pinnately lobed, bases cuneate, ultimate margins entire or toothed, abaxial faces hispid and strigillose to sericeous, adaxial faces strigillose and gland-dotted.
Pistillate heads
clustered, proximal to staminates; florets 1.
Staminate heads:
peduncles 0.5—2 mm; involucres shallowly cup-shaped (usually each with 1—5+ black nerves), 3—5(—7) mm diam., sparsely hirsute or glabrous; florets 6—12(—20+).
Burs:
bodies fusiform to obpyramidal, 3—5 mm, ± hirsutulous or glabrate, spines 8—18+, scattered, stoutly subulate (sometimes basally flattened or navicular), 2—4(—5) mm, tips straight or uncinate.
2
n
= 36.
Flowering (Apr—)Jul—Nov. Canyons, sandy flats, dunes; 10—3000 m; Alta., Man., Sask.; Ariz., Calif., Colo., Idaho, Kans., Minn., Mo., Mont., Nebr., Nev., N.Mex., N.Dak., Okla., Oreg., S.Dak., Tex., Utah, Wash., Wyo.
