Water hyacinth is a floating waterweed up to 65 cm tall and
the leaves are dark green rounded leaves up to 5–10 cm
in diameter. Leaf stalks of young plants are swollen into
spongy, bulbous structures; mature plants have elongated
leaf stalks.
An erect stalk supports a single spike of 8 to 15 flowers.
Flowers are light purple with a darker blue-purple with
yellow centres, 4–6 cm long and 3.5–5 cm wide. They are
carried in dense spikes projecting above the plant. Fruit
capsules are 10–15 mm long, contain up to 300 seeds.
Seeds are egg-shaped, 0.5–1.5 mm long. The root system
is extensive (up to 1 m) feathery, fibrous, black to purple.