Parthenium hysterophorus

Linnaeus

Sp. Pl. 2: 988. 1753.

Illustrated
Treatment appears in FNA Volume 21. Treatment on page 22. Mentioned on page 21.

Annuals, (10–)30–120+ cm. Leaf blades ovate to elliptic, 30–180+ × 10–50(–90+) mm, (1–)2-pinnately lobed (ultimate lobes lanceolate to linear, 3–50 × 2–15 mm), faces sparsely to densely scabrellous and gland-dotted (seldom with additional erect hairs 1–2 mm). Heads obscurely radiate, borne in open, paniculiform arrays. Peduncles 1–8(–15+) mm. Phyllaries: outer 5(–6), lance-elliptic, 2–4 mm, inner 5(–6) ovate to ± orbiculate, 2.5–4 mm. Pistillate florets 5(–6); corolla laminae reniform or orbiculate to oblong, 0.3–1 mm. Disc florets 12–30[–60]. Cypselae obovoid, 1.5–2(–3.5) mm; pappus-like enations erect, deltate to ovate, 0.5–1 mm (sometimes a third, subulate spur near apex adaxially). 2n = 34.


Phenology: Flowering Mar–Nov.
Habitat: Disturbed sites
Elevation: 0–300 m

Distribution

V21-36-distribution-map.gif

Ala., Ark., Conn., Del., D.C., Fla., Ill., Kans., La., Md., Mass., Mich., Miss., Mo., N.J., N.Mex., N.Y., Ohio, Okla., Pa., Tex., Va., Mexico, introduced in subtropical, tropical, and warm-temperate New World and Old World.

Discussion

In some places, especially in Old World, Parthenium hysterophorus causes serious contact dermatitis in humans. The plants should be handled with caution.

Selected References

None.

Lower Taxa

None.
... more about "Parthenium hysterophorus"
John L. Strother +
Linnaeus +
Ala. +, Ark. +, Conn. +, Del. +, D.C. +, Fla. +, Ill. +, Kans. +, La. +, Md. +, Mass. +, Mich. +, Miss. +, Mo. +, N.J. +, N.Mex. +, N.Y. +, Ohio +, Okla. +, Pa. +, Tex. +, Va. +, Mexico +, introduced in subtropical +, tropical +  and and warm-temperate New World and Old World. +
0–300 m +
Disturbed sites +
Flowering Mar–Nov. +
Illustrated +
Undefined (tribe Undefined) subtribe Ambrosieae +  and Undefined (tribe Undefined) subtribe Iveae +
Parthenium hysterophorus +
Parthenium +
species +