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


Nasturtium officinale (Watercress)

Kingdom:   Plantae
(Unranked):        Angiosperms
(Unranked):        Eudicots
(Unranked):        Rosids
Order:       Brassicales
Family:      Brassicaceae
Genus:      Nasturtium
Species:     N. officinale
Binomial name: Nasturtium officinale
Synonyms: Nasturtium nasturtium-aquaticum, Rorippa nasturtium-aquaticum, Sisymbrium nasturtium-aquaticum.
Common name: Kōwhitiwhiti, True cress, Watercress, Poniu

Nasturtium officinale is a fast-growing, aquatic or semi-aquatic, dicotyledonous, perennial herb native to Europe and Asia, and one of the oldest known leaf vegetables consumed by humans. It is a member of the family Brassicaceae, botanically related to the mustard family—noteworthy for a peppery, tangy flavour.
It is bright green, robust, creeping or upright, marginal aquatic herb common throughout New Zealand along the margins of slow flowing shallow waters. It can grow in water up to 6m in depth (Waikoropupu springs). Its habit can be moist banks, coastal areas, moist open pasture, and roadside drains. The green hollow floating stems of watercress are hairless and often produce roots at their lower joints.
The leaves are pinnately compound (2-12 cm long) are either deeply-lobed or once-compound with 1-5 pairs of lobes or leaflets.
In August - May small white and green flowers are arranged in loose elongated clusters, each flower has four white petals (3-6 mm long).
Nasturtium officinale siliques are straight or slightly curved (10-20 mm long and 2-2.5 mm wide) and are hairless and almost cylindrical in shape and are produced (August)-November-February-(May). Silique is a seed capsule of 2 fused carpels with the length being more than three times the width. Nasturtium officinale reproduces by seeds or vegetatively.
In some counties including New Zealand Nasturtium officinale is regarded as a weed, in other regions as an aquatic vegetable or herb.
Nasturtium officinale contains significant amounts of iron, calcium, iodine, and folic acid, in addition to vitamins A and C. Because it is relatively rich in Vitamin C, watercress was suggested (among other plants) by English military surgeon John Woodall (1570–1643) as a remedy for scurvy. Nasturtium officinale crops grown in the presence of manure can be a haven for parasites such as the liver fluke Fasciola hepatica and it is adviced that it is boiled before being eaten.
The Maori used it extensively in hangi to wrap food and as a vegetable. The leaves are cooked and eaten. They also use damp watercress tied in a cloth, applied to head for headaches.






 


Top surface of the leaves.


Underside of leaves.


A broken stem showing hollow centre which gives the plant it buoyancy.