Mercury Bay Weed

Botanical name: Dichondra repens
Synonyms: None in New Zealand
Common name(s): Mercury Bay Weed, Dichondra, Kidney Weed, Tom Thumb

About:
Dichondra repens is a low-growing, creeping perennial herb that forms a dense green carpet by rooting at the nodes as it spreads. It is valued as a hardy native groundcover and natural lawn alternative, particularly in lightly shaded areas. Its rounded kidney-shaped leaves and small greenish-white flowers create an attractive, soft-textured cover that tolerates light foot traffic and suppresses weeds once established.

Natural habitat:
Occurs naturally in forests, open woodland, grasslands, coastal areas and disturbed ground, often on fertile clay or clay-based soils. It is commonly found growing in lawns, along tracks and beneath open forest canopies.

Growing environment:
Thrives in full sun to partial shade in moist, well-drained soil. It tolerates a wide range of conditions but performs best with regular moisture. Suitable for coastal gardens and light frost areas.

Endemic distribution:
Indigenous to New Zealand. Found throughout the Three Kings Islands, North Island, South Island and Chatham Islands. Also naturally occurs in Australia and several islands of the south-west Indian Ocean.

Height:
2–5 cm

Width:
Spreading indefinitely by creeping stems.

Flowering:
September–February

Fruiting:
November–May

Uses:
• Native lawn alternative
• Groundcover beneath trees
• Filling gaps between pavers
• Rock gardens
• Banks and slopes
• Moist woodland gardens
• Erosion control

Appearance:
Growth habit:
A creeping perennial that rapidly forms dense mats by producing roots wherever its trailing stems contact the ground.

Leaves:
Small kidney-shaped to nearly circular leaves measuring 5–25 mm long. Soft green with fine greyish hairs on both surfaces, carried on slender stalks.

Flowers:
Tiny solitary star-shaped flowers are pale green to greenish-white and appear amongst the foliage, often going unnoticed because of their size.

Fruit:
Small, hairy, two-lobed seed capsules develop after flowering and release wind-dispersed seeds.

Ecology:
Seeds are dispersed primarily by wind, while the creeping stems allow the plant to spread vegetatively. The foliage provides habitat for small invertebrates, and the seeds are eaten by native waterfowl such as the Pacific black duck.

Associated habitats:
Forest margins, open woodland, grassland, coastal vegetation, lawns, garden edges and disturbed sites.

How to grow:
Plant in full sun or partial shade in reasonably fertile, free-draining soil. Water regularly while establishing. Once established it requires little maintenance apart from occasional trimming to maintain tidy edges. It performs best where it receives some moisture during dry periods.

Propagation:
Very easy to propagate from fresh seed or by dividing and transplanting rooted runners. Small sections establish quickly when kept moist.

Cultural use:
Although it has no widely recorded traditional Māori use, it is an important indigenous groundcover that contributes to healthy native ecosystems and is increasingly used in ecological landscaping.

Garden value:
An excellent native groundcover and one of New Zealand’s best low-growing lawn alternatives. It creates a lush green carpet, softens pathways and rockeries, suppresses weeds and provides a natural-looking finish in native gardens. It is particularly effective beneath trees and in areas where conventional lawn grasses struggle.