Parthenium hysterophorus |
Parthenium alpinum |
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ragweed parthenium, Santa Maria, Santa Maria feverfew, whitetop weed |
alpine feverfew, Arkansas River feverfew |
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Habit | Annuals, (10–)30–120+ cm. | Perennials, 1–2 cm (underground caudices 2–5+ cm, branched; plants cespitose or forming mats). |
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 oblanceolate to spatulate, 6–18(–35) × 1–3(–4+) mm, margins entire, faces strigilloso-sericeous (gray) and obscurely gland-dotted. |
Peduncles | 1–8(–15+) mm. |
0–5(–30) mm. |
Pistillate florets | 5(–6); corolla laminae reniform or orbiculate to oblong, 0.3–1 mm. |
5–8; corolla laminae 0 (tubes ± compressed, obscurely 2–4-lobed). |
Disc florets | 12–30[–60]. |
18–28+. |
Phyllaries | outer 5(–6), lance-elliptic, 2–4 mm, inner 5(–6) ovate to ± orbiculate, 2.5–4 mm. |
outer 5–8 ± linear, 4 mm, inner 5–8 ± orbiculate, 4–5 mm. |
Heads | obscurely radiate, borne in open, paniculiform arrays. |
± disciform, borne singly. |
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). |
oblanceoloid, 4 mm (narrowly winged); pappus-like enations 2, erect to spreading, ± subulate, 0.5–1 mm (a third, ± subulate element sometimes at apex of adaxial face). |
2n | = 34. |
= 36. |
Parthenium hysterophorus |
Parthenium alpinum |
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Phenology | Flowering Mar–Nov. | Flowering May–Jul. |
Habitat | Disturbed sites | Shale and calcareous outcrops, red clays |
Elevation | 0–300 m (0–1000 ft) | 1300–1700 m (4300–5600 ft) |
Distribution |
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]
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CO; NM; WY
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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.) |
Parthenium alpinum is in the Center for Plant Conservation’s National Collection of Endangered Plants. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 21, p. 22. | FNA vol. 21, p. 21. |
Parent taxa | Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Parthenium | Asteraceae > tribe Heliantheae > subtribe Ambrosiinae > Parthenium |
Sibling taxa | ||
Synonyms | Bolophyta alpina, P. tetraneuris, P. alpinum var. tetraneuris | |
Name authority | Linnaeus: Sp. Pl. 2: 988. (1753) | (Nuttall) Torrey & A. Gray: Fl. N. Amer. 2: 285. (1842) |
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