Introduction

PartheniumhysterophorusL. Family : Compositeae (Asteraceae) Common name : Congress Weed Tamil name : Vishapoondu Morphology : Broad leaved weed. Habit : Annual herb, up to 1.5 m Stem : Slender hairy Leaf : Leaves alternate, sessile, bipinnatifid, up to 20 x 10 cm, pubescent, lobes entire, acute Flower : Heads many, peduncled in panicles, florets  white, outer florets 5, female, supported by two hyaline wings at base; inner few male  florets; corolla in female an obovate, entire ligule; in male tubular, 5 lobed; anthers obtuse below Fruit : Fruit an achene, dorsally compressed, narrowed below; pappus of 2 lateral reflexed awns Propagation : By seed Habitat : Cultivated fields and road side

Parthenium (Partheniumhysterophorus L.) also known as  star weed, carrot weed, white cap, white top, etc. has been found growing naturally since centuries in Mexico, North and South America, Australia, China, Pacific islands, East and South Africa and Canada.  Till 1977, the weed did not find any place in the list of world's worst weeds. But, within the last decade, it has become one of the seven most dreaded weeds of the world.