Pistia stratiotes
Common name
water lettuce
Family
Araceae
Flora category
Vascular – Exotic
Structural class
Herbs - Monocots
Conservation status
Not applicable
Brief description
Free-floating aquatic plant, with thick pale green rounded leaves that form a rosette (lettuce like).
Distribution
Nationally eradicated, previously known from Tauranga and Hokianga, Northland.
Habitat
Still and slow-flowing water bodies in warm areas.
Wetland plant indicator status rating
Information derived from the revised national wetland plant list prepared to assist councils in delineating and monitoring wetlands (Clarkson et al., 2021 Manaaki Whenua – Landcare Research Contract Report LC3975 for Hawke’s Bay Regional Council). The national plant list categorises plants by the extent to which they are found in wetlands and not ‘drylands’. The indicator status ratings are OBL (obligate wetland), FACW (facultative wetland), FAC (facultative), FACU (facultative upland), and UPL (obligate upland). If you have suggestions for the Wetland Indicator Status Rating, please contact: [Enable JavaScript to view protected content]
OBL: Obligate Wetland
Almost always is a hydrophyte, rarely in uplands (non-wetlands).
Detailed description
Free floating perennial herb. Plants are stoloniferous with daughter plants often attached. Leaves are velvety hairy, pale yellow-green, often with a spongy thickened base. Roots are long and finely divided. Flowers are small (about 1 cm long) and inconspicuous, arranged as a spike enclosed by a hairy green bract.
Similar taxa
None.
Flowering
Late summer
Flower colours
Green, White
Fruiting
Not seen in New Zealand
Life cycle
Older stolons between individual plants decay to release young plants. Also spreads by seed overseas.
Year naturalised
1975
Origin
Throughout the tropics.
Reason for introduction
Ornamental pond and aquarium plant.
Control techniques
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.
Attribution
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.
DiTomaso JM, EA Healy (2003). Aquatic and riparian weeds of the west. University of California Agriculture and Natural Resources Publication 3421, 462pp.
Johnson PN, Brooke PA (1989). Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington. 319pp.
Connor, H. E.; Dawson, M. I.; Keating, R. D.; Gill L. S. (1996).