Ambrosia psilostachya
in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 5: 526. 1836.
Perennials, 10–60 (–100+) cm. Stems erect. Leaves proximally opposite, distally alternate; petioles 0–25 mm (often ± winged); blades deltate to lanceolate, 20–60 (–140) × 8–35 (–50+) mm, pinnately toothed to 1-pinnately lobed, bases cuneate to truncate, ultimate margins entire or toothed, abaxial and adaxial faces hirsutulous to strigose and glanddotted. Pistillate heads clustered, proximal to staminates; florets 1. Staminate heads: peduncles 0.5–2 mm; involucres obliquely cupshaped, 2–4 (–5) mm diam., hirsutulous; florets 5–15 (–30+). Burs: bodies ± obpyramidal to globose, 2–3 mm, hirsutulous, spines or tubercles 0 or 1–6, mostly distal, stoutly conic to acerose, (0.1–) 0.5–1 mm, tips straight. 2n = 18, 27, 36, 45, 54, 63, 72, 100–104, 108, 144.
Phenology: Flowering Jul–Oct(–Dec).
Habitat: Disturbed sites, often wet, alkaline, clay soils
Elevation: 0–2200 m
Distribution
Alta., B.C., Man., N.S., Ont., P.E.I., Que., Sask., Ala., Ariz., Ark., Calif., Colo., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., La., Maine, Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., S.C., S.Dak., Tenn., Tex., Utah, Vt., Wash., Wis., Wyo., Mexico (Baja California), Mexico (Chihuahua), Mexico (Coahuila)
Discussion
Hybrids between Ambrosia psilostachya and A. artemisiifolia have been called A. ×intergradiens W. H. Wagner. Some botanists consider the type of A. cumanensis Kunth (1818) to be conspecific with that of A. psilostachya.
Selected References
None.
Lower Taxa
"hirsutulous" is not a number.