Kingdom: Plantae
(unranked): Angiosperms
(unranked): Monocots
(unranked): Commelinids
Order: Commelinales
Family: Pontederiaceae
Genus: Eichhornia
Species: E. crassipes
Binomial name: Eichhornia crassipes
Synonymy: Piaropus crassipes
Common name: Water hyacinth, Common Water hyacinth, Water-orchid
All sightings must be reported to Biosecurity New Zealand on 0800 80 99 66.
Water hyacinth (Eichhornia crassipes) has been described as one of the worst weeds in the world - aquatic or terrestrial.
Water hyacinth is originally from the Amazon basin and in New Zealand, it is found in ponds, slow-moving streams and private backyard fishponds.It is reported as a weed in 56 countries including New Zealand. Introduced to the United States in 1890 and by the late 1950s, occupied 51,000 ha of Florida’s waterways. In ideal conditions, it grows at explosive rates exceeding doubling its populations in as little as 6-18 days. In large mats, degrades water quality and dramatically alters native plant and animal communities.
Water hyacinth plants consist of a free-floating rosette of shiny rounded leaves with thick masses of feathery roots which hang in the water. The roots are dark in colour and can reach 2.5 m in length. A single flowering stalk that grows up to 50 cm above the leaf canopy with a cluster of white to mauve-blue flowers (up to 5 cm wide). They have 6 petals, 6 stamens and each with a yellow spot. Plants produce floating horizontal stems from which new plants arise. Mature mats of this plant are held together by these stems.
This floating plant roots in mud if stranded, usually in dense mats with new plantlets attached on floating green stolons.The submerged roots are blue-black to dark purple, feathery, dense near root crown and tipped with long dark root caps.
Leaves formed in rosettes; petioles to 30 cm or more, spongy, usually inflated or bulbous, especially near base; leaf blades roundish or broadly elliptic, glossy green, to 15 cm wide. The fruit is a 3-celled capsule with many seeds.
It reproduces both vegetatively and sexually. Quickly forms new rosettes on floating stolons, with stolons easily broken; plants and mats transported by wind and water. Leaves are killed back by moderate freezes but it quickly regrows from the stem tip protected beneath the water surface.
Impact to Biota and Ecosystems
Eichhornia crassipes is aggressive and invasive by choking ponds and slow-moving water and replacing the natural flora. Twenty-five plants can produce a mat over 1 hectare of water in one temperate growing season.
Seeds and plants can be dispersed by water movement, wind, movement of machinery and equipment, and, planned or accidental planting and release by humans. Its dense mats, completely smothering large waterways and badly affecting water quality. These mats kill off native plants, attract breeding mosquitoes, block dams and irrigation systems, remove oxygen from the water and create a drowning risk for people and animals.
What to do
Water hyacinth is a notifiable Pest Plant and landowners/occupiers have a legal obligation to report the presence of this plant to Agri Quality and/or your local Pest Plant Officer who will arrange for the necessary eradication work. It is an offence for anyone to grow this plant.
Pest Plants are deemed to pose an intolerable threat to NZ and must be eradicated. The Government pays for and organises all eradication work needed on this plant. This plant is prohibited from propagation, sale and distribution within New Zealand.
For more details of this pest plant visit the Global Invasive Species Database at
http://www.issg.org/database/species/ecology.asp?si=70
All sightings must be reported to Biosecurity New Zealand on 0800 80 99 66.
MAF contracts a monitoring and control programme aimed at eliminating water hyacinth from New Zealand.
The swollen stolons give buoyancy to the plant
Photo showing the root mass underwater. These roots can hang down 2.5 metres 
Plant and root mass removed from a private fish pond. (Plant destroyed)
Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/
