Glyceria fluitans
Environmental Weed (2024)
Common names
floating sweetgrass
Biostatus
Exotic
Category
Vascular
Structural class
Grasses
Simplified description
Aquatic perennial emergent grass found on the margins of freshwaters on damp ground and swamps. It is characterised by its bright green leaf blades, and ability to form loose floating mats in shallow water.
Flower colours
Green
Detailed description
Perennial marginal aquatic grass, loosely tufted or forming loose masses in shallow water. Culm (20–)45–75 cm, erect or spreading, sometimes prostrate or floating at base. Leaf-blade bright green 10–23 cm, folded at first then becoming flat. Panicle (20–)30–55 cm.
Similar taxa
Very similar to Glyceria declinata. These two species can be distinguished when flowering as G. declinata has 3–5 distinct teeth on the lemma apex and the palea teeth exceed the lemma apex. G. fluitans has a rounded lemma and the palea does not exceed the lemma. G. maxima is a taller species, which has a distinct pointed ligule.
Distribution
Throughout New Zealand.
Habitat
Aquatic in drains and other slow flowing waterbodies. Damp ground in swamps and pastures, drains and river banks.
Conservation status
Not applicable
Detailed taxonomy
Family
Ecology
Flowering
Spring–summer.
Fruiting
Late spring-autumn
Year naturalised
1872
Origin
Europe and North America.
Reason for introduction
Pasture species, or contamination of other grass seed
Tolerances
Tolerant of very damp ground, physical damage, grazing, cold temperatures, and high nutrient levels. Intolerant of shade.
Control techniques
Can be controlled manually, mechanically or herbicidally depending on situation.
Life cycle and dispersal
Perennial. Seed and vegetative fragment spread by water movement. Reproduces by seed and rhizomes. Each flower head consists of an open panicle with 20–30 spikelets containing many seeds.
Seed and stem fragments spread within catchment via water flow. Contaminated diggers, livestock, soil movement, dumped vegetation, eel nets boats and trailers all spread seed and rhizomes 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’.
fluitans: From the Greek fluito (floating)
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.
GLYFLU
Referencing and citations
References and further reading
Coffey BT, Clayton JS. 1988. New Zealand water plants: a guide to plants found in New Zealand freshwaters. Ruakura Agricultural Centre, Hamilton, NZ. 65 p.
Johnson PN, Brooke PA. 1989. Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington, NZ. 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
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).