Vallisneria australis
NPPA pest plant
Common names
Eel grass
Synonyms
Vallisneria spiralis, V. gigantea, V. americana
Family
Hydrocharitaceae
Flora category
Vascular – Exotic
Structural class
Herbs - Monocots
Conservation status
Not applicable
Simplified description
Perennial submerged aquatic plant with long ribbon like leaves that emerge from the rooted base. New plants are formed vegetatively from rhizome extension.
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.
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]
OBL: Obligate Wetland
Almost always is a hydrophyte, rarely in uplands (non-wetlands).
Detailed description
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).
Life cycle
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.
Year naturalised
1897
Origin
Australia.
Reason for introduction
Ornamental aquarium plant
Control techniques
Notify regional council if found
Etymology
australis: Southern
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.
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.