Helosciadium nodiflorum
Environmental Weed (2024)
Common names
water celery, fool’s watercress
Biostatus
Exotic
Category
Vascular
Structural class
Herbs - Dicotyledons other than Composites
Simplified description
Sprawling emergent perennial aquatic plant that can grow over a metre in height, with bright green leaves arranged in pairs up each stem, and white flowers close to leaf bases.
Flower colours
White
Detailed description
Stout perennial herb with prostrate and ascending stems. The stems are hollow, finely furrowed, may be up to 2m long and root at the lower nodes. The leaves are glossy, bright green to 70 cm long with 2 to 8 pairs of toothed stalkless oval to lance-shaped leaflets. The individual flowers are small (2 to 2 mm) with five white petals, and occur in short stalked clusters/umbels (2 to 4 cm) in diameter. The fruit are dark brown, small (2mm long) and ovoid/egg shaped and ribbed.
Similar taxa
Wild celery (Apium graveolens), New Zealand celery (Apium prostratum) and Watercress (Nasturtium spp.). Wild celery is similar but does not root at the nodes, and NZ celery has thicker three lobed and shortly pinnate leaves.
Distribution
Scattered distribution from Northland to Wellington, abundant in many areas. Has also established in the north and west of the South Island.
Habitat
Shallow water ponds, drains, and the margins of slow moving streams.
Conservation status
Not applicable
Detailed taxonomy
Family
Synonyms
Apium nodiflorum (L.) Lagasca
Ecology
Flowering
November to February
Fruiting
Late summer to autumn
Year naturalised
1947
Origin
Native to Britain, central Europe, Asia and North Africa.
Reason for introduction
Possibly seed contaminant or contaminant of ornamental pond plants.
Tolerances
Seed germinate on damp substrates.
Control techniques
Can be controlled manually, mechanically or herbicidally depending on situation (Newman, 2004).
Life cycle and dispersal
Seed germinate on damp substrates. Regrows from detached shoots, which readily form roots, and from seed.
It can be mistaken for watercress and be collected and distributed as such.
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
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.
HELNOD
Referencing and citations
References and further reading
Johnson PN, Brooke PA (1989). Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington. 319pp.
Newman J (2004), Information sheet 28: Fools watercesss. Centre for Ecology and Hydrology , UK.
Popay et al (2010). An illustrated guide to common weeds of New Zealand, third edition. NZ Plant Protection Society Inc, 416pp.
Johnson, A. T., Smith, H. A. (1972). Plant Names Simplified: Their pronunciation, derivation and meaning. Landsman Bookshop Ltd: Buckenhill, UK.
Attribution
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).