Species

Vallisneria australis

Etymology

australis: southern

Common Name(s)

eel grass

Authority

Vallisneria australis S.W.L.Jacobs & Les

Family

Hydrocharitaceae

Brief Description

Perennial submerged aquatic plant with long ribbon like leaves that emerge from the rooted base. New plants are formed vegetatively from rhizome extension.

Flora Category

Vascular - Exotic

Structural Class

Monocotyledonous Herbs

Synonyms

Vallisneria spiralis, V. gigantea, V. americana

Distribution

Locally naturalised in North Island and Marlborough in the South Island.

Habitat

Moderately fast flowing to still water bodies. Colonises lake-bed sediment in water up to 9m deep.

Features

The leaves are thick and strap-like and arise from long creeping stems. Leaves are up to 3 m long and between 0.5 and 5 cm wide. The leaf tips (when not browsed) are obtuse to acute, with fine toothed margins towards the apex. Male plants are only known from Lake Pupuke, with female plants also confirmed there. Male flowers (a translucent sheath surrounding many tiny yellow flowers) being produced in the leaf bases. All other naturalised populations are female, the female flowers are green and cylindrical borne on long, often spiral, filamentous stalks arising in the leaf bases and extending to the waters surface.

Similar Taxa

Sagittaria subulata, S. platyphylla, and swamp lily (Ottelia ovalifolia). The submerged leaves of these species look similar to the submerged leaves of eel grass; however, eelgrass never has emergent leaves or conspicuous white flowers.

Flowering

Summer to autumn

Flower Colours

Green

Fruiting

Viable seed not produced in NZ (only male plants present here).

Year Naturalised

1897

Origin

Australia.

Reason for Introduction

Ornamental aquarium plant

Control Techniques

Notify regional council if found

Life Cycle and Dispersal

Spread by stolon fragmentation. There is no evidence of viable seed production in New Zealand. A potentially important submerged weed; poor dispersal capacity has limited current spread.

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.

This page last updated on 21 Aug 2013