Oenanthe aquatica
Common names
horsebane
Biostatus
Exotic
Conservation status
Not applicable
Category
Vascular
Structural class
Herbs - Dicotyledons other than Composites
Simplified description
Upright to sprawling floating marginal perennial aquatic plant up to 1.5 m tall. Foliage is finely divided and hemlock-like, stems are hollow and reddish in colour. Submerged leaves are finely divided with threadlike segments.
Flower colours
Red/Pink, White
Detailed description
Biennial to perennial sprawling or erect herb up to 1.5 m tall, either floating (sometimes with submerged foliage) or terrestrial. Stems hollow, slightly grooved, usually tinged reddish purple. Emergent leaves bi to 4-pinnate, with segments up to 10 mm long, segments either crenate or pinnatifid. Submerged leaves 3-4 pinnate with filiform pinnae. Flowers in an umbel, either terminal or opposite a leaf 1-5 cm diameter, with (3)-5-12 rays. Subtending bracts 1 - (3) or lacking. Flowers white or pink tinged c. 2 mm diameter. Fruit ovoid-cylindric 3-5 mm long, prominantly ribbed.
Similar taxa
American horsebane (Oenanthe sarmentosa) and water celery (Apium nodiflorum) have less divided leaves with longer segments. Both species for dense sprawling mats, with stems rooting at the nodes.
Distribution
Locally common in Marlborough.
Habitat
Still and slow flowing water bodies, marshes and seasonally flooded wetlands.
Detailed taxonomy
Genus
Family
Endemic family
No
Ecology
Flowering
Summer
Fruiting
Summer-autumn
Year naturalised
1940
Origin
Europe and Western Asia
Reason for introduction
Unknown, possibly a seed contaminant
Control techniques
Not controlled in New Zealand.
Life cycle and dispersal
Seed floating and dispersed by water.
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
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.
OENAQU
Referencing and citations
References and further reading
Johnson PN, Brooke PA (1989). Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington. 319pp.
Attribution
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).