T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Nasturtium microphyllum (Narrow-fruited Watercress)

Kingdom:   Plantae
(Unranked):        Angiosperms
(Unranked):        Eudicots
(Unranked):        Rosids
Order:       Brassicales
Family:      Brassicaceae
Genus:      Nasturtium
Species:     N. microphyllum (microphyllum: small leaf)
Binomial name: Nasturtium microphyllum
Synonyms: Dictyosperma olgae, Nasturtium officinale var. olgae, Nasturtium officinale var. microphyllum, Nasturtium uniseriatum, Pirea olgae, Rorippa microphyllum, Rorippa nasturtium-aquaticum subsp. microphylla ,  
Common name: Narrow-fruited Watercress, One rowed watercress, Kōwhitiwhiti, Watercress,

Nasturtium micro is a bright green, robust, creeping or upright dicotyledonous herb that has small white flowers in spring through summer, and is found along the margins of slow flowing shallow waters. It is common throughout New Zealand on the margins of slow-moving rivers, streams, ditches and drains.
The leaves are glabrous, all similar, but become smaller near inflorescence and have a distinctive peppery smell when crushed.
Nasturtium microphyllum is very similar to Nasturtium officinale, but the flowers of Nasturtium microphyllum are larger, the siliqua is longer and more slender, and the seeds are in one row and with more finely pitted surfaces. The leaves and stems of Nasturtium microphyllum turn brown/purplish in autumn.

Maori rapidly incorporated watercress into their diet as a boiled green, preferring it to the introduced garden cabbage. One can gather the edible fresh green leaves anytime. Avoid plants growing in water that drains from fields where animals, particularly sheep, graze. Due to the risk of watercress being infested with the deadly liver fluke parasite, if unsure, cooking the leaves will destroy any parasites and render the plant perfectly safe to eat.

The stems are hollow which helps the plant float.

New roots forming on a stem.

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/