Vascular – Exotic
Free floating fern with tightly overlapping hairy leaves, that forms dense growths on still and slow flowing waters.
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.
Still and slow flowing water bodies in warm areas. Prefers warm growing conditions and is susceptible to frost damage in a severe winter.
Wetland plant indicator status rating
OBL: Obligate Wetland
Almost always is a hydrophyte, rarely in uplands (non-wetlands).
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.
The juvenile form resembles Azolla spp, but it is very distinctive when mature.
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).
South America, southeastern Brazil, and northern Argentina.
Reason for introduction
Ornamental aquarium plant
Notify Ministry for Primary Industries if found.
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.
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 P. et al. 2020. Freshwater Invasive Species of New Zealand 2020. NIWA publication. https://docs.niwa.co.nz/library/public/FreInSpec.pdf.