Distribution, Biology and Ecology of Parthenium hysterophorus L. (Congress Grass) an invasive species in the North-Western Indian Himalaya (Himachal Pradesh)

Parthenium hysterophorus L. is a native plant of sub-tropical America and it is rapidly invading in the North-Western Indian Himalaya (Himachal Pradesh), from last two decades onwards. Here, it invaded up-to 2000 m altitude from mean sea level and drastically effecting native plant resources in the invaded habitats.  The density and dominance of the P. hsterophorus has been higher in the summer and was nearly absent during the winter season in the NW Himalaya. The average height of the plants of P. hysterophorus was recorded up-to 2.09 ± 0.27 m and its root system deep up-to 17.32 ± 4.03 cm below the ground level. It produced an enormous number of seeds which will help in its invasion in to various habitats. It was measured that one single plant of Parthenium produced more than 7397 ± 81.42 seeds during one season. The seeds were lighter in weight and were 2.31 ± 0.02 mm in length and 1.03 ± 0.01 mm in width. In the NW Himalaya P. hysterophorus completed its two life cycles in one year, that is, from March to June and from July to November.   Key words: Invasive species, North-Western Himalaya, Parthenium hysterophorus