Watercress
Nasturtium officinale
NEMBA category
English: Watercress, Common Water Cress, Water Cress, Green Watercress, Wild Watercress
Afrikaans: Sterkkos, Brongras, Bronkhorstslaai, Bronkors, Bronslaai, Stercors, Waterkers
Sesotho: Kerese
Historical scientific names: Rorippa nasturtium-aquaticum, Sisymbrium nasturtium-aquaticum, Nasturtium aquaticum
Nasturtium officinale, commonly known as Watercress, is a fast-growing, aquatic or semi-aquatic perennial herb native to Europe and Asia. It is characterised by its small, rounded, dark green leaves and clusters of white, four-petaled flowers.
While valued as a nutritious edible plant, it is considered an invasive alien species in South Africa. It spreads rapidly through vegetative fragments and seeds, forming dense mats in streams, rivers, and wetlands. These mats can out-compete native aquatic vegetation, disrupt water flow, and alter habitats, posing a threat to local biodiversity and ecosystem health, particularly in sensitive wetland areas.
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Origin:
Native to Europe and Asia.
Distinguishing features:
Aquatic/semi-aquatic habit: Grows predominantly in or very close to clear, slow-moving water, often forming dense mats.
Hollow stems: Its stems are typically hollow, which helps them to float.
Pinnately compound leaves with rounded leaflets: Leaves are divided into several rounded to oval, glossy dark green leaflets, with the terminal leaflet usually larger.
Small white flowers in clusters: Delicate white flowers with four petals, arranged in small spikes.
Overall appearance:
A sprawling, herbaceous perennial plant that grows in aquatic or semi-aquatic environments. It forms dense, bright green mats with stems that trail, float, or rise above the water surface, often rooting at the nodes.
Height:
Stems can grow up to 60 centimetres long, often trailing or floating, with leaves and flowers typically rising about 10 to 30 centimetres above the water.
Width:
Can spread indefinitely, forming large, dense patches across suitable aquatic habitats if left unchecked.
Leaves:
Alternate, pinnately compound (meaning they are divided into several smaller leaflets arranged along a central stalk), typically 5 to 15 centimetres long. Each leaf usually has 3 to 9 (most commonly 5 to 7) somewhat fleshy, glossy dark green leaflets. The leaflets are rounded to oval, with the leaflet at the very end usually being larger and more rounded. The leaves have a distinct peppery, slightly bitter taste when crushed or eaten.
Flowers:
Small (about 4 to 6 millimetres in diameter), delicate white flowers, each with four petals arranged in a cross shape, which is characteristic of the mustard family. They are borne in small, dense clusters (racemes) at the tips of the stems or in the leaf axils. The plant is hermaphroditic, meaning each flower has both male and female parts.
Flowering season:
In South Africa, it can flower for most of the year in suitable cool, wet conditions, but it is particularly prolific during spring and summer (around September to March).
Fruits:
The fruits are small, slender, elongated pods (called siliques), which are typical of the mustard family. They measure about 1 to 2.5 centimetres long and 2 to 3 millimetres wide and are usually held erect or slightly spreading on the plant.
Seeds:
Numerous, very small (about 1 millimetre in size), brownish-red, and typically oval to kidney-shaped with a minutely pitted surface. They are contained within the fruit pods and are released when the pods split open. Seeds can be dispersed by water currents, by animals, or through human activities like dumping garden waste.
Bark:
Not applicable, as Nasturtium officinale is a herbaceous plant with soft, hollow stems, not bark.
Thorns:
This species does not have thorns.
Wood:
Not applicable; it is a herbaceous plant, not woody.
Roots:
Produces a fibrous root system that readily develops from the nodes (joints) along its stems. This allows it to easily root in the mud or submerged substrates, making it very effective at spreading.
Soil type:
Requires consistently moist or submerged, well-aerated, and often nutrient-rich soil or substrate. It thrives in clear, cool, and often slow-moving water.
Aspect:
Prefers full sun to partial shade. It flourishes in areas with cool, flowing water, such as streams, springs, and irrigation ditches.
Ediblity:
Widely cultivated and consumed globally as a leafy green vegetable. It is popular in salads, sandwiches, soups, and as a garnish due to its distinctive pungent, peppery flavour.
Toxicity:
Generally considered safe for consumption by humans, and is valued for its high nutritional content. However, it is crucial to only consume watercress from clean, unpolluted water sources. Wild watercress can accumulate harmful nitrates or heavy metals if the water is contaminated. Unwashed wild watercress may also carry parasites like liver flukes, which can be harmful to humans if ingested.
Uses:
Primarily cultivated and harvested as a popular culinary herb and leafy vegetable, highly valued for its distinctive flavour and rich nutritional profile (including high levels of vitamins A, C, and K, and various minerals and antioxidants). Historically, it has also been used in various traditional medicine systems for its purported health benefits.
Ecology:
As an alien invasive plant in South Africa, Nasturtium officinale is a significant threat to indigenous aquatic ecosystems. It forms dense, sprawling mats in clear, slow-moving streams, rivers, irrigation canals, and wetlands. Its rapid growth rate, efficient vegetative propagation (even small stem fragments can root and grow), and prolific seed production allow it to quickly outcompete and displace native aquatic and riparian vegetation. These dense mats can significantly alter water flow, reduce sunlight penetration, decrease oxygen levels in the water (harming fish and other aquatic life), and block waterways, negatively impacting overall aquatic biodiversity.
Distribution and habitat:
Widely cultivated for food and has become extensively naturalised throughout South Africa in areas with suitable permanent water sources. It is common in all provinces where aquatic habitats exist, including the Eastern Cape (frequently found in streams, rivers, ditches, and wetlands around Kenton-on-Sea), Western Cape, KwaZulu-Natal, Mpumalanga, Limpopo, and Gauteng. It invades clear, shallow, slow-moving water bodies such as streams, springs, ditches, and riverbanks.
Derivation of name:
The genus name Nasturtium comes from the Latin 'nasus tortus', which literally means "twisted nose." This refers to the plant's pungent, biting taste, which can make one's nose wrinkle.
The species epithet officinale is Latin for "of the shops" or "officinal," indicating that the plant was historically recognised and sold for its medicinal or culinary uses.
The common name "Watercress" directly describes its aquatic habitat and its classification as a "cress" (a type of plant known for its pungent leaves).
Historical aspects:
Watercress has been cultivated and consumed as a food source for centuries, prized for its peppery flavour and nutritional value. It was introduced to many parts of the world, including South Africa, for culinary purposes. Its ability to escape cultivation and thrive in a wide range of aquatic environments, coupled with its rapid growth and spread, quickly led to its naturalisation and subsequent recognition as an invasive species in many regions where it is not indigenous.
NEMBA status: Category 2 invasive species. This means it is an invasive species with commercial value that may be grown in demarcated areas under a permit. It must be grown in a contained environment, and its spread outside of these areas must be prevented.
Interesting facts:
This plant is famous for its peppery, spicy flavour, which is why it's a popular ingredient in salads and sandwiches!
Don't let its humble look fool you: Watercress is a superfood! It's packed with more Vitamin C than oranges and more calcium than milk!
It absolutely loves water – you'll almost always find it growing with its feet wet, in streams, rivers, or soggy ground.
Even though it's super tasty, it's a bit of a bully in the water, growing so fast and thick that it can push out other plants and even block waterways!
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