The New Zealand Plant Conservation Network

Species

Oenanthe sarmentosa

Etymology

sarmentosa: twiggy

Common Name(s)

American horsebane

Authority

Oenanthe sarmentosa DC.

Family

Apiaceae

Brief Description

Sprawling floating marginal perennial aquatic plant up to 1.5 m tall. Foliage is divided but less so than horsebane, stems are hollow and green in colour.

Flora Category

Vascular - Exotic

Structural Class

Dicotyledonous Herbs other than Composites

Distribution

Locally common in the vicinity of Greymouth, Westland.

Habitat

Stream edges and swamps.

Features

Biennial to perennial sprawling herb up to 1.5 m tall, with floating stems hollow, grooved, green, usually rooting at the nodes. Emergent leaves bipinnate, tripinnate on lower branches with segments up 10-35 mm long, segments lobed. Submerged leaves absent. Flowers in an umbel, either terminal or opposite a leaf 2-5 cm diameter, with 10-20 rays. Subtending bracts 1 or lacking. Flowers white c. 2 mm diameter. Fruit cylindric 2.5-3.5 mm long, prominantly ribbed.

Similar Taxa

Horsebane (Oenanthe aquatica) and water celery (Apium nodiflorum). Horsebane has more divided leaves with shorter segments. Water celery has less divided (pinnate) leaves.

Flowering

Summer

Flower Colours

White

Fruiting

Summer-autumn

Year Naturalised

1975

Origin

W. North America

Reason for Introduction

Unknown, possibly a seed contaminant

Control Techniques

Not controlled in New Zealand.

Life Cycle and Dispersal

Vegetative spread by stoloniferous growth and by floating seeds.

This page last updated on 21 Aug 2013