The green links below add additional plants to the comparison table. Blue links lead to other Web sites.
enable glossary links

ragweed parthenium, Santa Maria, Santa Maria feverfew, whitetop weed

American feverfew, wild feverfew, wild quinine

Habit Annuals, (10–)30–120+ cm. Perennials, 30–60(–100+) 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).

blades ovate to lanceolate, 30–350+ × 20–120+ mm, margins usually crenate to serrate, sometimes coarsely toothed or somewhat lobed (then mostly toward bases), faces hispid to hirtellous or ± scabrous, gland-dotted.

Peduncles

1–8(–15+) mm.

1–8(–12+) mm.

Pistillate florets

5(–6);

corolla laminae reniform or orbiculate to oblong, 0.3–1 mm.

5(–6);

corolla laminae ovate to oblong or orbiculate, 1–2+ mm.

Disc florets

12–30[–60].

15–35+.

Phyllaries

outer 5(–6), lance-elliptic, 2–4 mm, inner 5(–6) ovate to ± orbiculate, 2.5–4 mm.

outer 5(–6) lanceolate to broadly ovate, 3–5 mm, inner 5(–6) ± orbiculate, 4–6 mm.

Heads

obscurely radiate, borne in open, paniculiform arrays.

radiate, borne in corymbiform to paniculiform arrays.

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).

± obovoid, 3–4+ mm; pappus-like enations 0 or 2(–4), erect to spreading, ± subulate or threadlike, fragile, 0.3–0.6+ mm.

2n

= 34.

= 72.

Parthenium hysterophorus

Parthenium integrifolium

Phenology Flowering Mar–Nov. Flowering May–Sep.
Habitat Disturbed sites Glades and barrens, prairies, disturbed sites
Elevation 0–300 m (0–1000 ft) 10–500 m (0–1600 ft)
Distribution
from FNA
AL; AR; CT; DC; DE; FL; IL; KS; LA; MA; MD; MI; MO; MS; NJ; NM; NY; OH; OK; PA; TX; VA; Mexico [Introduced in subtropical, tropical, and warm-temperate New World and Old World]
[WildflowerSearch map]
[BONAP county map]
from FNA
AL; AR; CT; GA; IA; IL; IN; KS; KY; LA; MA; MI; MN; MO; MS; NC; NY; OH; OK; PA; SC; TN; TX; VA; WI; WV
[WildflowerSearch map]
[BONAP county map]
Discussion

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

(Discussion copyrighted by Flora of North America; reprinted with permission.)

As evidenced by the synonymy, Parthenium integrifolium as here circumscribed has been variously partitioned by other taxonomists. For the present, I see no justification for segregating species from, or for formal recognition of infraspecific taxa within P. integrifolium.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 21, p. 22. FNA vol. 21, p. 22.
Parent taxa Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Parthenium Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Parthenium
Sibling taxa
P. alpinum, P. argentatum, P. confertum, P. incanum, P. integrifolium, P. ligulatum
P. alpinum, P. argentatum, P. confertum, P. hysterophorus, P. incanum, P. ligulatum
Synonyms P. auriculatum, P. hispidum, P. hispidum var. auriculatum, P. integrifolium var. auriculatum, P. integrifolium var. henryanum, P. integrifolium var. hispidum, P. integrifolium var. mabryanum, P. radfordii
Name authority Linnaeus: Sp. Pl. 2: 988. (1753) Linnaeus: Sp. Pl. 2: 988. (1753)
Web links