Vascular – Exotic
Herbs - Monocots
Perennial free-floating aquatic plant, capable of forming dense floating mats of vegetation in still or slow-flowing waterbodies. Plants are rosettes of glabrous leaves, below which a mass of roots hang in the water column. The inflated, spongy leaf stalks provide floatation. Plants are linked by a network of stems to form a dense mat. Flowers are showy, six-lobed, pale lilac in colour, with a deep blue-bordered yellow spot on the uppermost lobe.
Mostly northern parts of NZ, subject to a national eradication programme since 1950’s with few populations now remaining.
Still and slow flowing water bodies in warm areas.
Wetland plant indicator status rating
OBL: Obligate Wetland
Almost always is a hydrophyte, rarely in uplands (non-wetlands).
Free floating perennial herb. Plants are stoloniferous with daughter plants often attached. Leaves are bright green, often with a spongy inflated petiole. Roots are long and finely divided, and are bright purple when young before becoming black. Flowers are large (7 cm in diameter) in a spike of up to 10 flowers. They are blue-purple with a central yellow eye surrounded by a dark ring on the uppermost petal. The inflorescence stalk (peduncle) bends underwater when fertilized to release many small, ribbed seeds that sink to the bottom sediments after the capsule disintegrates.
mid summer to early autumn
Older stolons between individual plants decay to release young plants; the young plants can flower in 3-4 weeks. This species also reproduces by seed. Germination of seeds occurs when hydrosoils are exposed, in shallow water or on stranded mats of the plant. Late summer germination of water hyacinth has been noted at several New Zealand sites. Seeds and plants can be dispersed by water movement, wind, movement of machinery and equipment, and, planned or accidental planting and release by humans.
South America, Amazon basin, western Brazil.
Reason for introduction
Ornamental pond plant
Notify Ministry for Primary Industries if found.
National Pest Plant Accord species
This plant is listed in the 2020 National Pest Plant Accord. The National Pest Plant Accord (NPPA) is an agreement to prevent the sale and/or distribution of specified pest plants where either formal or casual horticultural trade is the most significant way of spreading the plant in New Zealand. For up to date information and an electronic copy of the 2020 Pest Plant Accord manual (including plant information and images) visit the MPI website.
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).
References and further reading
Champion et al (2012). Freshwater Pests of New Zealand. NIWA publication. http://www.niwa.co.nz/freshwater-and-estuaries/management-tools/identification-guides-and-fact-sheets/freshwater-pest-species.
Johnson PN, Brooke PA (1989). Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington. 319pp.
Coffey BT, Clayton JS (1988). New Zealand water plants: a guide to plants found in New Zealand freshwaters. Ruakura Agricultural Cente. 65pp.
Kasselmann C (2003). Aquarium plants. Krieger Publishing company, Florida, 518pp.; Hofstra D, P Champion, (2006). Management options assessment for Eichhornia crassipes. NIWA client Report HAM2006-163.
Hofstra D, P Champion, (2006). Organism Consequence Assessment Eichhornia crassipes. NIWA Client Report: HAM2006-058a.