Salvinia molesta

Common Name(s)

water fern


Salvinia molesta D.S.Mitch.



Brief Description

Free floating fern with tightly overlapping hairy leaves, that forms dense growths on still and slow flowing waters.

Flora Category

Vascular - Exotic

Structural Class



Locally naturalised, subject to a national eradication programme since 1983, first record from Western Springs, Auckland in 1963.


Still and slow flowing water bodies in warm areas. Prefers warm growing conditions and is susceptible to frost damage in a severe winter.


Free-floating fern. Salvinia has a horizontal stem with paired aerial (above the water) leaves. Adult leaves brownish-green elliptic to broadly elliptic up to 2.5 x 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 lond, 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.



Flower Colours

No Flowers



Year Naturalised



South America, southeastern Brazil, and northern Argentina.

Reason for Introduction

Ornamental aquarium plant

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)


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.


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

This page last updated on 21 Aug 2013