Also known as
water fern, Kariba weed, S. herzogii
Where is it originally from?
What does it look like?
Free-floating fern (<30cm) with two leaves above the water and one rootlike leaf below. Two leaf types: juvenile leaves well-spaced, small, lying on surface (occasionally only these leaves are produced), while more common rounded mature leaves (1-4 x 1-5cm) are crowded, compacted, folded about the midrib, and the upper surfaces have many rows of water-repellent, basket-like hairs.
Are there any similar species?
The juvenile form resembles Azolla species
Why is it weedy?
Phenomenal growth rate (can double in 8 days), fragments easily, can survive in damp mud. Tolerates water of any quality, and increased nutrients increase growth rate. Frost-tender, requires high light, high temperature.
How does it spread?
Does not produce spores, spreads by fragmentation only through water movement, deliberate 'liberation' of aquarium contents into ponds or lakes.
What damage does it do?
Covers water surface, blocking light to native species. Rotting vegetation and normal growth consumes oxygen, quickly stagnating water and killing all fauna and flora below. Blanket effect prevents oxygenation by wind. Can harbour other diseases.
Which habitats is it likely to invade?
Potential to invade any slow-moving or still freshwater habitat in upper North Island.
What can I do to get rid of it?
Report any suspected sightings to your regional council.