Parthenium hysterophorus |
|
|---|---|
|
ragweed parthenium, Santa Maria, Santa Maria feverfew, whitetop weed |
|
| Habit | 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). |
| Peduncles | 1–8(–15+) mm. |
| Pistillate florets | 5(–6); corolla laminae reniform or orbiculate to oblong, 0.3–1 mm. |
| Disc florets | 12–30[–60]. |
| Phyllaries | outer 5(–6), lance-elliptic, 2–4 mm, inner 5(–6) ovate to ± orbiculate, 2.5–4 mm. |
| Heads | obscurely radiate, borne in open, 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). |
| 2n | = 34. |
Parthenium hysterophorus |
|
| Phenology | Flowering Mar–Nov. |
| Habitat | Disturbed sites |
| Elevation | 0–300 m [0–1000 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]
|
| 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.) |
| Parent taxa | |
| Sibling taxa | |
| Name authority | Linnaeus: Sp. Pl. 2: 988. (1753) |
| Source | FNA vol. 21, p. 22. |
| Web links |
|