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 An
Illustrated Guide to
Common Weeds
of New Zealand
Egeria
densa
egeria
Family
HYDROCHARITACEAE
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.
Available from Nationwide Book Distributors
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.
Habitat
Still, shallow, enriched
water in dams, ponds, drains, streams, rivers and lakes, in depths
of up to 5 m.
Distribution
Abundant in Waikato
hydro lakes, scattered elsewhere in NI, and occasional, but spreading
in SI. Originally from South America.
Comments
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.
Derivation
Egeria (Lat.)
= after a Roman goddess of water; densa (Lat.) = dense.
Web-notes:
Weed Links
On this site
Reproduced from Common Weeds
of New Zealand:
External Links
 Weedbusters
New Zealand
- Weedbusters is a weeds awareness and education programme that aims to
protect New Zealand's environment from the increasing weed problem.
- AgPest
- A free tool to assist farmers and agricultural professionals in decision-making regarding weed and pest identification, biology, impact and management.
 New 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.
 New
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
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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