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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 Bruce Roy, Ian Popay, Paul Champion, Trevor James & Anis Rahman
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 Manaaki-Whenua
Press and Touchwood
Books
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.
 New
Zealand Plant Conservation Network Weeds Fact Sheets
- Search for 1500 weed fact sheets mainly derived from the Department of
Conservation's BIOWEB weeds database.
 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."
-
 New
Zealand Landcare Trust
- Plant Pest information including Pictures, Distribution Maps, References,
Environmental Effects and Control.
-
- New
Zealand Aquatic Weeds
- Hosted by the weed management group of NIWA (National Institute of Water
and Atmospheric Research).
-
- Weed
Control Manual for the Bay of Plenty
- Weeds information compiled by Environment Bay of Plenty.
-
 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.
-
- Canterbury
Weed Guide
- A weed identification guide prepared by the Christchurch City Council.
-
- Australian
Plants as Weeds
- Part of the Association of Societies for Growing Australian Plants website.
- Department
of Agriculture Western Australia
- Collection of weed resources from the Department of Agriculture, Government
of Western Australia
- Weed
Society of Victoria
- Promoting wider awareness and interest in weeds and their management.
Includes a useful page of links
to other weed societies.
-
- Tamar
Valley Weeds Strategy
- Listing of common and botanical names, images, and information including
control methods for weeds found in Tasmania, and also on the Australian
mainland.
-
-
- New
Jersey Weed Gallery, USA
- Listing of common and botanical names and images, plus a small amount
of information for weeds that cause problems in the USA.
- Invasive
and Exotic Species of North America
- Images and other information from the University of Georgia.
- University
of California
- Weed Photo Gallery, with common and botanical names.
-
- World
of Weeds
- Weed-related resources including weed science, practical tools, gardening
tips about controlling weeds, and environmental news updates.
-
- Invasive
Species Specialist Group
- "The ISSG aims to reduce threats to natural ecosystems and the native
species they contain by increasing awareness of invasive alien species,
and of ways to prevent, control or eradicate them."
-
- Invasive
Woody Plants
- Collection of research and associated literature for invasive woody plants
in the tropics and the temperate zone.
-
- WeedScience.com
- Site that includes a comprehensive collection of weed images from around
the world.
-
-
 Books
on Weeds from FetchBook.Info
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