Glyceria maxima
Environmental Weed (2024)
Common names
floating sweetgrass, reed sweetgrass
Biostatus
Exotic
Category
Vascular
Structural class
Grasses
Simplified description
Robust bright green grass, up to nearly 2 m tall, with creeping rhizomes that form large patches excluding all other plants. The tip of the leaf is boat-shaped. The seedheads are open and branched with many spikelets. The sheath has obviously cross veins.
Flower colours
Green
Detailed description
Perennial aquatic grass, to 1.8 m tall. Root system extensive up to c. l m deep, as well as sprawling underground stems. Leaves shiny, hairless and mid-green in colour; 0.7–2 cm wide, growing 30–60 cm above the water surface; end in an abrupt point, edges are rough to touch. Flower head open, branched, 15–45 cm long comprising a large number of spikelets that range from yellow to green in colour, with a purplish tinge. Seeds small, dark brown, produced prolifically throughout summer and autumn.
Similar taxa
Glyceria declinata and G. fluitans. Both of the other Glyceria species present in New Zealand are much smaller (up to 50 cm tall) with narrow sparingly branched, distinctively brown seedheads and form low clumps as opposed to the tall erect clumps formed by reed sweetgrass.
Distribution
Widely naturalised, abundant in most lowland parts of North Island, more scattered and absent from much of South Island.
Habitat
Aquatic in drains and other slow flowing waterbodies, often forming dense floating mats in open frost-free areas. Also in swamps.
Conservation status
Not applicable
Detailed taxonomy
Family
Poaceae
Ecology
Flowering
Spring–summer.
Fruiting
Late spring–autumn
Year naturalised
1906
Origin
Europe
Reason for introduction
Pasture species
Tolerances
Tolerant to physical damage, grazing and pollutants. Intolerant of heavy frost and shade.
Control techniques
Can be controlled manually, mechanically or herbicidally depending on situation.
Life cycle and dispersal
Perennial. Spread by seed and rhizomes. Prolific seed production. Seeds and rhizome via water flow. Contaminated diggers, livestock, soil movement, dumped vegetation, eel nets, boats and trailers all spread seed and fragments into new catchments.
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).
Other information
Etymology
glyceria: From the Greek glykos ‘sweet’.
Environmental Weed (2024)
This plant is named in a list of 386 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.
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.
GLYMAX
Referencing and citations
References and further reading
Champion P. et al. 2020. Freshwater Invasive Species of New Zealand 2020. NIWA publication. https://docs.niwa.co.nz/library/public/FreInSpec.pdf
Coffey BT, Clayton JS. 1988. New Zealand water plants: a guide to plants found in New Zealand freshwaters. Ruakura Agricultural Cente. 65 p.
Johnson PN, Brooke PA. 1989. Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington. 319 p.
Champion P, James T, Popay I, Ford K. 2012. An illustrated guide to common grasses, sedges and rushes of New Zealand. NZ Plant Protection Society Inc, Christchurch, NZ. 182 p.
Attribution
Prepared by Paul Champion and Deborah Hofstra (NIWA)