Parthenium hysterophorus

Scientific nameParthenium hysterophorus
English: carrot weed, carrot grass, congress weed, famine weed, ragweed, white top.
Annual erect herb, much branched [0.5–1.5 (–2) m high], forms a basal rosette of leaves when young, green stems are longitudinally grooved or ribbed and covered in short hairs.
Leaves: Pale green, covered with short stiff hairs; rosette and lower stem leaves are deeply divided and large (3–30cm long and 2–12 cm wide); upper stem leaves are shorter and less divided
Flowers: White, in small compact heads (5 mm across), clustered at the tips of branches, each flowerhead has five distinctive petals.
Fruits: Achenes (small, dry, one-seeded fruits that don’t open at maturity), (1.5–2.5 mm long), five in each flowerhead.
Argentina, Bahamas, Barbados, Belize, Bolivia, Cuba, Dominica, Grenada, Grenadines, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Paraguay, Puerto Rico, St. Vincent, Trinidad and Tobago, Uruguay, Virgin Islands and Venezuela.
Medicine, ornament and accidentally as a contaminant.
Roadsides, railways, wasteland, disturbed land, fallow land, crops, plantations, managed pasture, gardens drainage ditches, forest edges/gaps, woodland edges/gaps, grassland, savannah, riversides, lowlands and gullies.
Parthenium disrupts grasslands, invades woodlands and generally disturbs native vegetation through aggressive competition (Evans, 1997). Parthenium is allelopathic, reducing crop yields, and displacing palatable species in natural and improved pasture. In India, parthenium infestations have resulted in yield losses of up to 40% in several crops (Khosla and Sobti, 1979). Parthenium is also a secondary host for a range of crop pests. In terms of pasture production, this noxious weed has been found to reduce livestock carrying capacities by as much as 90% (Jayachandra, 1971). It also poses serious health hazards to livestock, and can cause severe allergenic reactions in people who regularly come into contact with the weed.
Witt, Arne. 2017. Guide to the Naturalized and Invasive Plants of Southeast Asia. CAB International. Retrieved from on 23 October 2018
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Last updated on 02/14/2019 22:32