Species

Oenanthe aquatica

Common Name(s)

horsebane

Authority

Oenanthe aquatica (L.) Poiret

Family

Apiaceae

Brief 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.

Flora Category

Vascular - Exotic

NVS Species Code

OENAQU

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.

Structural Class

Dicotyledonous Herbs other than Composites

Distribution

Locally common in Marlborough.

Habitat

Still and slow flowing water bodies, marshes and seasonally flooded wetlands.

Features

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.

Flowering

Summer

Flower Colours

Red / Pink,White

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.

Attribution

Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).

References and further reading

Johnson PN, Brooke PA (1989).  Wetland plants in New Zealand.   DSIR Field Guide, DSIR Publishing, Wellington. 319pp.

This page last updated on 21 Aug 2013