the tiny native watercress of NZ's cool stream margins
- Size
- Height: 20–50 cm
- Lifespan
- 2–3 years
- Diet
- Not applicable (herb). Photosynthetic.
- Habitat
- Wetlands, stream banks, lake margins, swamps and damp pasture. Prefers moist, fertile soils with full sun to partial shade. Tolerates seasonal flooding.
- Range
- Throughout New Zealand from Northland to Stewart Island. Most common in wetlands, stream banks and damp areas. Also found worldwide in temperate regions.
- Endemism
- Native
- Main Threats
- Habitat loss from wetland drainage is the primary threat. Water pollution and degradation. Climate change affecting wetland habitats. Competition from introduced watercress.
- Population
- Populations are considered stable but localised. The species is common in wetlands throughout New Zealand. It is threatened by habitat loss and competition from introduced watercress. Protection of wetlands is important.
- Conservation Status
- Not Threatened
A wild relative of introduced watercress, this plant has a similar peppery flavour but is less common. The leaves and stems are edible and can be used in salads, sandwiches and soups. It grows in wetlands, stream banks and damp areas. It is threatened by habitat loss and competition from introduced watercress, which is more aggressive. A native losing ground to a faster cousin.
The leaves are divided into several pairs of leaflets, with a larger terminal leaflet. They are dark green and glossy, similar to introduced watercress but smaller and more finely divided. The stems are hollow and ribbed, and they root at the nodes when they contact wet soil. A plant that spreads by touching the ground.
The flowers are small and yellow, appearing in summer. They are followed by slender pods that contain the seeds. The seeds are dispersed by water, floating on the surface of streams and wetlands. A plant that travels with the current.
Native watercress is less common than introduced watercress, which has become naturalised in many waterways. The introduced species is more aggressive and outcompetes the native in many areas. Native watercress is also threatened by habitat loss, as wetlands are drained for agriculture and urban development. A plant that is losing the race.
To find native watercress is to search the edges of wetlands and streams. Look for the small, peppery leaves, the yellow flowers, the creeping stems. It is a plant of the clean water, a sign of a healthy stream. Where it grows, the water is likely clean and unpolluted.
The stream is clear. The watercress grows along the edge, small and peppery. The introduced cousin is not far away, larger, faster, taking over.
The native does not fight back. It just grows. It has been here longer. It hopes that counts for something.