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 An
Illustrated Guide to
Common Weeds
of New Zealand
Ceratophyllum
demersum
hornwort
Family
CERATOPHYLLACEAE
 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,
free-floating or lightly anchored, rootless, delicate aquatic perennial.
Has forked, finely divided leaves. Forms very dense under-water
masses of vegetation in freshwater up to 10 m deep.
- Flowers Green
(female), whitish (male), no petals, minute. Solitary in leaf
axils, stalkless, with ten to twenty stamens, adapted for underwater
pollination.
- Fruit Black
oval nuts 5 mm long, with one terminal and two basal spines.
- Leaves Dark
green, up to 4 cm long, in whorls of seven to twelve densely crowded
at the stem apex and increasingly spaced down stems. Leaves equally
forked once or twice into rather stiff, tapering segments.
- Stems Floating,
submerged, up to 1.5 m long, branched, stiff and rather brittle.
Readily broken by waves, current or boats to float away and establish
in shallow water.
- Roots
No roots, lightly anchored in sediment by buried leaves and stems.
Habitat
Still or slow-flowing
freshwater of lakes, lagoons, ponds, rivers and drains.
Distribution
Locally abundant in
the Waikato River system including hydro lakes. Common in Auckland,
Waikato, Rotorua Lakes, Taupo, Hawkes Bay and Wellington in NI.
Found throughout the world.
Comments
May be confused with
parrot's feather (Myriophyllum aquaticum) which has pinnate,
rather than forked leaves. Listed on the National
Pest Plant Accord (see Introduction for details).
Derivation
of botanical name
Ceratophyllum (Gr.)
= horned leaved, the leaves resembling antlers; demersum (Lat.)
= submerged.
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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