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Water hyacinth is a free-floating aquatic plant that can grow in dense mats. The leaves are glossy, green, leathery and up to 8cm across. The leaf stems are swollen and spongy and act like floats. Each plant has a mass of purple roots. It produces an attractive spike of up to ten large, lilac-mauve flowers, each with a yellow spot in the centre of one of the petals.
Water hyacinth grows in still or slow moving freshwater, such as ponds, streams, swamps and dams. In New Zealand, water hyacinth has been most common on small, nutrient-enriched waterbodies.
Water hyacinth forms dense mats which can completely smother waterways and reduce water quality. The mats exclude native plants, block dams and waterways, impede drainage and disrupt recreational activities. Water hyacinth is frost-tender but the dense mats tolerate moderate frosts.
Water hyacinth reproduces from seeds which may remain viable for 20 years. It also reproduces vegetatively - young plants can grow from roots and can produce seed within 3-4 weeks.