Eel grass
Hydrocharitaceae - Vallisneria australis
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What does it look like?

Eelgrass is a submerged, bottom-rooted freshwater plant.  It produces long, thick, strap-like leaves that are up to 3m long and 0.5-5cm wide.  The leaves never extend above the surface of the water.  Both male and female plants are known from Lake Pupuke (Auckland) but other known infestations comprise only female plants.  Male flowers consist of large pollen-filled sacs produced at the base of mature plants.  Female flowers are small and green and produced on the end of a very long, spirally coiled stalk that can extend to the water’s surface. 

Eelgrass can be found in moderately-fast flowing water and still water bodies.  It forms dense beds that displace native plants, may affect recreational activities, impede navigation and obstruct water out-takes.

Why is it a problem?

Eelgrass forms dense beds that out-compete and displace native plants.  In New Zealand, it is generally spread through intentional planting.

There is no evidence of viable seed production occurring in New Zealand, although both male and female plants exist in Lake Pupuke (Auckland).  It spreads from root fragments.

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