Salvinia molesta
NPPA pest plant
Common names
water fern
Biostatus
Exotic
Conservation status
Not applicable
Category
Vascular
Structural class
Ferns
Simplified description
Free floating fern with tightly overlapping hairy leaves, that forms dense growths on still and slow flowing waters.
Detailed description
Free-floating fern. Stem horizontal with paired aerial (above the water) leaves. Adult leaves brownish-green elliptic to broadly elliptic up to 2.5 × 2 cm, folded, whereas young leaves are flat. Aerial leaves have hairs shaped like miniature egg-beaters. Lower submerged leaves look more like roots and can be up to 30 cm long. Sporocarps in long, straight chains, hairy c. 1 mm diameter produced under water.
Similar taxa
The juvenile form resembles Azolla spp, but it is very distinctive when mature.
Distribution
Introduced and Naturalised. New Zealand: North Island (ponds and lakes from Northland to Waikato, subject to a national eradication programme since 1983, first record from Western Springs, Auckland in 1963). A widespread species which has become a serious weed in tropical regions.
Habitat
Still and slow flowing water bodies in warm areas. Prefers warm growing conditions and is susceptible to frost damage in a severe winter.
Detailed taxonomy
Genus
Family
Endemic family
No
Ecology
Year naturalised
1964
Origin
South America, southeastern Brazil, and northern Argentina.
Reason for introduction
Ornamental aquarium plant
Tolerances
Leaves are frost sensitive but can survive over winter in warmer parts. Generally requires high ligh and high temperature. Tolerates any quality of water, nutrient increases growth rate.
Control techniques
Notify Ministry for Primary Industries if found.
Life cycle and dispersal
Perennial. Spreads rapidly by fragmentation and producing plantlets from the old end of the horizontal axis, and can grow from a singe node; the death and decay of the older connecting part of the plant can lead to the separation of the viable younger branches. The plant is apparently a sterile hybrid. Fragments spread by water movement, deliberate release (with fish from aquaria).
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).
Other information
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.
Referencing and citations
References and further reading
Champion P. et al. 2020. Freshwater Invasive Species of New Zealand 2020. NIWA publication. https://docs.niwa.co.nz/library/public/FreInSpec.pdf.
Attribution
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).