Alternanthera philoxeroides
NPPA pest plant
Environmental Weed (2024)
Common names
alligator weed
Synonyms
Telanthera philoxeroides
Family
Amaranthaceae
Flora category
Vascular – Exotic
Structural class
Herbs - Dicotyledons other than Composites
NVS code
The National Vegetation Survey (NVS) Databank is a physical archive and electronic databank containing records of over 94,000 vegetation survey plots - including data from over 19,000 permanent plots. NVS maintains a standard set of species code abbreviations that correspond to standard scientific plant names from the Ngä Tipu o Aotearoa - New Zealand Plants database.
ALTPHI
Conservation status
Not applicable
Simplified description
Sprawling emergent perennial herb. Leaves are bright green and waxy. They are between 5-10 cm long, up to 2 cm wide, and arranged in opposite pairs on the stem. The white flower looks like a small clover flower and is at the end of a longish stalk. Stems are thick, soft, and hollow, often with a reddish tinge.
Distribution
Locally abundant in parts of Northland and Auckland regions. Scattered distribution in Waikato, Bay of Plenty and single sites known from Horizons, Canterbury and West Coast.
Habitat
Warm still and slow flowing water bodies, swamps, ponds, stream banks, dune hollows, flooded pasture and cropping land and urban lawns. It will tolerate a wide habitat range including brackish water, amongst pasture and terrestrial crops.
Wetland plant indicator status rating
Information derived from the revised national wetland plant list prepared to assist councils in delineating and monitoring wetlands (Clarkson et al., 2021 Manaaki Whenua – Landcare Research Contract Report LC3975 for Hawke’s Bay Regional Council). The national plant list categorises plants by the extent to which they are found in wetlands and not ‘drylands’. The indicator status ratings are OBL (obligate wetland), FACW (facultative wetland), FAC (facultative), FACU (facultative upland), and UPL (obligate upland). If you have suggestions for the Wetland Indicator Status Rating, please contact: [Enable JavaScript to view protected content]
FACW: Facultative Wetland
Usually is a hydrophyte but occasionally found in uplands (non-wetlands).
Detailed description
An almost glabrous rhizomatous perennial herb, growing either as terrestrial or rooted emergent, or free flowing aquatic plant. Stems are 10-70cm long often forming large densely interwoven mats. Leaves are dark green, opposite, sessile, linear, 2 to 7 cm long, 5 to 40 mm wide. Flowers are silvery-white, 1.2 to 1.4 cm dia. borne on stalks 2 to 7 cm long rising from the leaf axis. Root is short and filamentous in water, rising mainly from nodes, longer & thicker in soil often extending below 50 cm.
Similar taxa
Two native Alternanthera species (A. nahui) and lesser joyweed (A. denticulata), Senegal tea (Gymnocoronis spilanthoides), and primrose willow (Ludwigia peploides). The native Alternanthera species are smaller, with the flowers lacking stalks and located at the base of paired leaves whereas the stalk (peduncle) on A. philoxeroides can be up to 9 cm long. Senegal tea has serrated and wavy leaf margins. Primrose willow has alternate leaves.
Flowering
Flowering is not known to occur in NZ. Midsummer till March in Australia (Parsons & Cuthbert, 2001)
Flower colours
White
Fruiting
Seed set is unknown in New Zealand.
Life cycle
Reproduction is vegetative by the extension of prostrate stems or stem fragmentation. The floating fringe of marginal mats is also readily fragmented and dispersed. Machinery (e.g. for mechanical drain clearance) has been shown to spread stem fragments between catchments. Seed set is unknown in New Zealand.
In Australia, seeds are produced, but rarely viable under local conditions (Parsons & Cuthbertson, 2001).
Potentially spread by people mistaking weed for mukunu-wenna (A. sessilis) which is occasionally used as a vegetable.
Year naturalised
1906
Origin
Native to South America.
Reason for introduction
Accidental, contamination of ballast
Control techniques
Method of control is dependent on the scale/size of the infestation and the habitat (e.g.., the nature of the watercourse). Notify regional council if found (except Northland and Auckland where this plant is widespread)
Tolerances
Highly tolerant of poor drainage. Tolerant of drought and shade. Slightly tolerant of frost. It will also re-sprout from grazing and other physical damage.
Etymology
alternanthera: From the Latin alternus ‘alternate’ and the Greek anthera ‘anther’, meaning alternating anther, probably in reference to the anthers being alternately fertile and barren.
National Pest Plant Accord species
This plant is listed in the 2020 National Pest Plant Accord. The National Pest Plant Accord (NPPA) is an agreement to prevent the sale and/or distribution of specified pest plants where either formal or casual horticultural trade is the most significant way of spreading the plant in New Zealand. For up to date information and an electronic copy of the 2020 Pest Plant Accord manual (including plant information and images) visit the MPI website.
Environmental Weed (2024)
This plant is named in a list of environmental weeds in New Zealand 2024 prepared by DOC. 759 candidate species were considered for inclusion on this new comprehensive list of environmental weeds in New Zealand. The species considered were drawn from published lists of weed species, lists of plants that must be reported or managed by law if observed, existing national and regional programmes and agreements for pest management, and species already managed by the Department of Conservation (DOC). Candidate species were then assessed to see if they were fully naturalised and whether they have more than minor impacts in natural ecosystems. Read the full report here.
Attribution
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).
References and further reading
Champion et al (2012). Freshwater Pests of New Zealand. NIWA publication. http://www.niwa.co.nz/freshwater-and-estuaries/management-tools/identification-guides-and-fact-sheets/freshwater-pest-species.
Johnson PN, Brooke PA (1989). Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington. 319pp.
Coffey BT, Clayton JS (1988). New Zealand water plants: a guide to plants found in New Zealand freshwaters. Ruakura Agricultural Cente. 65pp.
Popay et al (2010). An illustrated guide to common weeds of New Zealand, third edition. NZ Plant Protection Society Inc, 416pp.
Timmins, S., McKenzie, I. (1995). Weeds in New Zealand Protected Natural Areas Database.(Department of Conservation technical series, 1172-6873 ;
no. 8). Department of Conserservation: Wellington.
Johnson, A. T., Smith, H. A. (1972). Plant Names Simplified: Their pronunciation, derivation and meaning. Landsman Bookshop Ltd: Buckenhill, UK.