A student was fascinated with the beautiful mauve colored flowers of water hyacinth, he asked his teacher to allow him to take a few plants to his village pond, but teacher denied him to do so because:

It is an invasive weed species.

The correct answer is Option (4) → It is an invasive weed species. 

The beautiful mauve-colored flowers found on very appealingly-shaped floating plants in water bodies. These plants which were introduced into India for their lovely flowers have caused havoc by their excessive growth by causing blocks in our waterways. They grow faster than our ability to remove them.

These are plants of water hyacinth (Eichhornia crassipes), the world’s most problematic aquatic weed, also called ‘ Terror of Bengal ’. They grow abundantly in eutrophic water bodies, and lead to an imbalance in the ecosystem dynamics of the water body. When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive, and cause decline or extinction of indigenous species. Examples of invasive weed species are carrot grass (Parthenium), Lantana and water hyacinth (Eicchornia).