Water hyacinth is related to

Answer: (c) Eichhornia

Water hyacinth = Eichhornia crassipes.

The idea

Three common weeds float free on Indian ponds. Each is known by its scientific name in older textbooks.

Eichhornia → water hyacinth: swollen leaf stalks, lilac flowers → Pistia → water lettuce: a rosette like a small lettuce → Lemna → duckweed: tiny green discs → Salvinia → a floating fern

Why the others are wrong

(a) Lemna is duckweed.

(b) Pistia is water lettuce.

The trap

All three are floating water weeds — you have to know the genus.

Also know

Water hyacinth and Salvinia are among the worst invasive water weeds in India. They are controlled by removing them by hand or machine and by releasing weevils that feed only on them.