Horticulture Heading

 

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

 

Alternanthera philoxeroides
alligator weed

Family AMARANTHACEAE

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 Touchwood Books

Alternanthera philoxeroides - alligator weed

Aquatic perennial, forming dense floating mats on fresh or brackish water, and also creeping onto wet dune hollows and cropping land near waterways. Soft, hollow stems up to 2 m long. Opposite leaves 5-10 cm long. White flowers similar to white clover, but smaller.

  • Flowers White, small papery florets in six- to twenty-flowered, clover-like heads up to 13 mm in diameter. Flower heads solitary on stalks up to 9 cm long in leaf axils, or on short stalks at the ends of the branches. Flowers Dec-Feb.
  • Fruit Not produced in NZ and reproduction is only from stem fragments.
  • Leaves Waxy, elliptical to egg-shaped, 5-10 cm long, margins entire, in opposite pairs, stalkless or with a short leaf stalk. A ring of white hairs is found between the bases of the opposite leaves.
  • Stems Thick, soft, hollow, grooved, reddish, branching, to 10 m or more long, floating or creeping. Stem tips upright, as much as 1 m above the water.
  • Roots Fibrous, stems root from lower nodes.

Habitat

Warm, shallow, enriched, fresh to slightly brackish water of drains, swamps, ponds, lagoons, stream banks, dune hollows.

Distribution

NI only. Abundant in North Auckland waterways especially around Kaipara Harbour, Auckland City, Waikato River mouth and one or two sites in Waikato and Bay of Plenty. Originally from Brazil.

Comments

Likely to spread further south as a serious weed of waterways and of nearby crops. Insects introduced as biological control agents give good control in lakes, but not on wet land. Listed on the National Pest Plant Accord (see Introduction for details).

Related species

Nahui (Alternanthera sessilis), native to NZ, is much smaller, with stalkless axillary flower heads, occurring in damp open places, rarely in dry waste areas and gardens, locally throughout NI, and in the Lake Forsyth area in Canterbury.

Derivation of botanical name

Alternanthera (Lat.) = alternate anthers (the anthers are alternatively fertile and sterile); philoxeroides (derivation unknown).

Get Acrobat Reader

Web-notes: Weed Links

On this site

Reproduced from Common Weeds of New Zealand:

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.
PestWebNZ™
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 naturalise 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.
 

 
 
 
Weeds in Australia
Weeds website of the Australian Government.
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 weeds of national significance.
 

Invasive and Exotic Species of North America
Images and other information from the University of Georgia.

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."
WeedScience
Site that includes a comprehensive collection of weed images from around the world.
 


FetchBook.Info Home PageBooks on Weeds from FetchBook.Info

More Plant Profiles

Home | Journal | Newsletter | Conferences
Awards | Join RNZIH | RNZIH Directory | Links

© 2000–2019 Royal New Zealand Institute of Horticulture
Last updated: July 13, 2014