Vascular – Exotic
Herbs - Dicotyledons other than Composites
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.
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.
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.
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
FACW: Facultative Wetland
Usually is a hydrophyte but occasionally found in uplands (non-wetlands).
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.
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 is not known to occur in NZ. Midsummer till March in Australia (Parsons & Cuthbert, 2001)
Seed set is unknown in New Zealand.
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.
Native to South America.
Reason for introduction
Accidental, contamination of ballast
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)
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.
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.
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.