Paspalum distichum
Environmental Weed (2024)
Common names
Mercer grass
Biostatus
Exotic
Category
Vascular
Structural class
Grasses
Simplified description
Floating grass forming dense mats, with typical two-pronged lowerheads produced in summer.
Flower colours
Green
Detailed description
Creeping, perennial, mat-forming grass, the stems sprawl along the ground and then grow to 60 cm tall. Stolons long, rooting frequently, with rhizomes. Leaves are distantly alternate, the lamina is 4-10 cm long and 2-6mm wide, tip pointed, bluish-green, soft and lax, slightly hairy above and below, rolled and hairy at base. Ligule up to 4 mm, membrane-like, whitish-translucent, often torn. Auricle absent. Sheath with reddish-purple tinge. Seedhead of 2 (sometimes 1 or 3) diverging, erect racemes, 25–50 mm long; with softly hairy spikelets.
Similar taxa
Kikuyu grass (Cenchrus clandestinus). Differs from Mercer grass in that Kikuyu grass lacks a membranous ligule and has a short flowering head that is almost enclosed within the leaves. In contrast, Mercer grass has a very distinctive forked flowering head.
Distribution
Locally common in the North Island but also in the South Island as far south as Canterbury.
Habitat
Still and slow flowing water bodies and wetland margins.
Conservation status
Not applicable
Detailed taxonomy
Family
Poaceae
Synonyms
Paspalum paspalodes
Ecology
Flowering
November, December, January, February
Fruiting
Late summer
Year naturalised
1887
Origin
Europe
Reason for introduction
Forage grass for wet areas
Tolerances
Tolerates wet, hot to mod-cool, wind, damage and grazing, most soils. Intolerant of frost, deep shade and dry conditions.
Control techniques
Not usually controlled in New Zealand, but may be controlled by mowing or herbicidally.
Life cycle and dispersal
Perennial. Reproduces by seed and stem fragmentation. Seeds freely, seed viability unknown. Dispersed by water, livestock pelts and hooves (possibly seed in dung). Contaminated diggers and dumped vegetation.
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]
FACW: Facultative Wetland
Usually is a hydrophyte but occasionally found in uplands (non-wetlands).
Other information
Etymology
paspalum: The Greek name for millet
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.
PASDIS
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
Attribution
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).