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Book cover - Common Weeds of New ZealandAn Illustrated Guide to
Common Weeds
of New Zealand


Egeria densa


Reproduced from
Common Weeds of New Zealand
by Ian Popay, Paul Champion & Trevor James
ISBN 0 473 09760 5
by kind permission of the
New Zealand Plant Protection Society

Publication or other use of images or descriptive text on these pages is unauthorised unless written permission is obtained from the authors and publisher.
Appropriate acknowledgement of the publication Common Weeds of New Zealand must always be given.

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Egeria densa - egeria

Wholly submerged, bottom-rooted, vigorous, aquatic perennial. Occurs in fresh water and can be up to 5 m tall in still water. One of the oxygen weeds, denser than Elodea and Lagarosiphon.

  • Flowers White, conspicuously protruding just above surface, up to 20 mm in diameter. Flowers have three petals 4-12 mm long and nine golden stamens. Flowers occur in the axils of the upper leaves, two to three enclosed in a spathe. Only male flowers are found in NZ.
  • Fruit Fruits not seen in NZ. Reproduction by regrowth from stem fragments.
  • Leaves Very dark green, up to 4 cm long, in whorls of four to six. Leaves abruptly narrowed to a pointed tip.
  • Stems Buoyant, slender, brittle, 3 mm in diameter. Stems up to 1 m or more long, much-branched, with nodes becoming closer together towards the stem tips.
  • Roots Bottom rooted.


Still, shallow, enriched water in dams, ponds, drains, streams, rivers and lakes, in depths of up to 5 m.


Abundant in Waikato hydro lakes, scattered elsewhere in NI, and occasional, but spreading in SI. Originally from South America.


Likely to spread to new waterways. Listed on the National Pest Plant Accord (see Introduction for details). The oxygen weeds include Egeria, Elodea and Lagarosiphon. In Egeria the leaves are dark green, in whorls of four or five and 12-30 mm long. The flowers are white, conspicuous and emerge above the water.


Egeria (Lat.) = after a Roman goddess of water; densa (Lat.) = dense.


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Web-notes: Weed Links

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External Links

WeedbustersWeedbusters New Zealand
Weedbusters is a weeds awareness and education programme that aims to protect New Zealand's environment from the increasing weed problem.
A free tool to assist farmers and agricultural professionals in decision-making regarding weed and pest identification, biology, impact and management.
Weed keyNew Zealand Weeds Key
An interactive identification key to the weeds of New Zealand. Developed at Landcare Research.

New Zealand Plant Conservation Network naturalised plants
Search for information on more than 2500 naturalised and weedy plants.
NZ Plant Protection SocietyNew Zealand Plant Protection Society
Their main objective: "To pool and exchange information on the biology of weeds, invertebrate and vertebrate pests, pathogens and beneficial organisms and methods for modifying their effects."
Massey UniversityMassey University Weeds Database
A site providing information about New Zealand weeds and weed control. It has a series of pages showing pictures of New Zealand weeds, notes on identification and control. It also provides information on a university paper entitled Controlling Weeds.

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Last updated: March 1, 2021