The New Zealand Plant Conservation Network

Species

Alternanthera philoxeroides

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.

Common Name(s)

alligator weed

Authority

Alternanthera philoxeroides (Mart.) Griseb.

Family

Amaranthaceae

Brief 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.

Flora Category

Vascular - Exotic

NVS Species Code

ALTPHI

Structural Class

Dicotyledonous Herbs other than Composites

Synonyms

Telanthera philoxeroides

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.

Features

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.

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)

Life Cycle and Dispersal

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.

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.

This page last updated on 31 Jul 2014