Common Rush

Botanical name: Juncus edgariae
Synonyms: Juncus gregiflorus, Agathryon edgariae
Common name(s): Common rush, Edgar’s rush, wīwī

About:
A robust, highly variable perennial rush and the most common indigenous Juncus species in New Zealand. Juncus edgariae forms compact to rather open tussocks of upright, smooth, glossy stems ranging from bright or dark green through orange-green to reddish-green.

It is one of New Zealand’s characteristic wetland and damp-ground rushes, occurring from the coast into alpine environments. It readily colonises disturbed wet ground, pasture and urban sites and can form substantial colonies through rhizomatous growth and prolific seed production.

The species was historically confused with Juncus gregiflorus, which is now considered endemic to Australia.

Natural habitat:
Coastal to alpine, reaching approximately 1,600 m elevation, although most abundant from coastal to montane environments.

Common around wetland margins, seasonally damp ground, open shrubland, riparian areas, swamp margins, wet pasture, drainage channels and disturbed ground.

It is also capable of colonising urban environments and modified agricultural landscapes.

Growing environment:
Full Sun, Wet Soil, Heavy Soil, Seasonal Inundation, Frost, Wind & Coastal Exposure tolerant.

Prefers open, sunny sites with permanently or seasonally damp soil but is capable of tolerating relatively dry periods once established.

It grows particularly well in heavy or poorly drained soils where many other native species struggle.

Endemic distribution:
Endemic to New Zealand.

Occurs on the Kermadec Islands, North Island, South Island, Stewart Island/Rakiura and Chatham Islands.

It has also become naturalised in Britain.

Height:
60 cm–2.5 m.

Width:
Approximately 50 cm–1.5 m or more, depending on growing conditions and age. Colonies may become considerably broader through rhizomatous spread and seedling establishment.

Flowering:
October–December.

Produces numerous small brownish-green flowers in apparently lateral inflorescences. The flower clusters are extremely variable, ranging from loose, highly branched structures to compact clusters or a single dense spherical head.

Fruiting:
November–April.

Produces numerous small, dark golden-brown capsules approximately 1.5–2.3 mm long.

Uses:
• Wetland restoration
• Riparian revegetation
• Stream and river margins
• Pond and dam margins
• Stormwater systems
• Rain gardens and swales
• Erosion control
• Bank stabilisation
• Revegetation of poorly drained land
• Wildlife habitat
• Naturalistic native landscapes
• Restoration of seasonally wet ground

Care should be taken near productive pasture because established plants can spread vigorously and livestock generally avoid grazing the tough stems.

Appearance:
Growth habit:
A rhizomatous perennial rush forming compact to diffuse upright tussocks.

The horizontal rhizome is approximately 5 mm in diameter and grows at or immediately beneath the soil surface, anchoring mature plants strongly into the ground.

Plants vary considerably in appearance according to habitat and geographical origin.

Leaves:
True leaves are absent.

The upright flowering stems provide the main photosynthetic surface.

Basal bracts tightly sheath the lower stems and are dark reddish-brown toward the base, becoming straw-coloured higher up. The uppermost sheath may be somewhat looser.

Flowers:
Flowering culms are approximately 1–3 mm in diameter, erect, wiry, smooth and distinctly glossy. They become particularly hard when dry.

Stem colour varies considerably from bright green and dark green to orange-green or reddish-green, usually drying to a glossy yellow-green.

The stems have approximately 22–60 fine longitudinal striations. Internally, they contain dense white pith that is usually irregularly interrupted, although occasionally almost continuous.

The apparently lateral inflorescence varies greatly in form. It may be open and extensively branched, with small clusters of flowers at the branchlet tips, condensed into a central cluster accompanied by several stalked lateral clusters, or reduced to a single compact spherical head more than 10 mm across.

Individual flowers are approximately 1.5–2 mm long with six brownish-green tepals that become brown with age.

Three stamens are normally present.

Fruit:
Capsules are approximately 1.5–2.3 mm long and equal to or shorter than the surrounding tepals.

They are ellipsoid to obovoid, becoming dark golden-brown when mature, with a darker brown, blunt to slightly indented tip carrying a small terminal point.

Seeds are approximately 0.4–0.6 mm long.

The mucilaginous seeds are dispersed by water, wind and attachment to animals or other moving objects.

Ecology:
Juncus edgariae is one of the most ecologically important and widespread native rushes in New Zealand’s wet and seasonally wet environments.

Dense tussocks provide shelter and structural habitat for wetland invertebrates and other small animals, while the rhizomatous root system helps bind saturated soils and reduce erosion along waterways and wetland margins.

It is particularly successful in disturbed environments and readily colonises exposed wet soil following vegetation clearance or changes in drainage.

Although primarily associated with wetlands, it is sufficiently adaptable to tolerate periodically drier ground and is classified as a facultative wetland species.

Associated habitats:
Freshwater wetlands, swamp margins, riparian zones, stream banks, river margins, seasonally wet pasture, open shrubland, drainage channels, wet hollows, pond margins and disturbed urban ground.

Common native associates can include Apodasmia similis, Carex maorica, Carex secta, Carex virgata, Eleocharis acuta and Phormium tenax.

How to grow:
Very easy to establish and exceptionally hardy.

Plant in full sun in damp to wet soil. It tolerates heavy clay, periodic inundation, exposure, wind and frost and is therefore particularly valuable for difficult restoration sites.

Water regularly during initial establishment if the site is not naturally wet. Once established, plants are capable of surviving temporary dry periods.

Allow adequate space because mature plants can become substantial and may spread beyond their original planting position.

For ecological restoration, it is particularly useful in the middle and upper margins of wetlands where water levels fluctuate seasonally.

Propagation:
Easily propagated from fresh seed or division.

Surface-sow fresh seed onto consistently moist propagation media and maintain moisture throughout germination.

Established plants can also be divided by separating healthy sections of rhizome with attached stems and roots. Divisions establish rapidly when replanted into moist ground.

Because the species can spread readily, propagation is rarely difficult.

Cultural use:
Wīwī is a Māori name applied to several native rushes and similar wetland plants.

Rushes were traditionally important sources of fibre and were associated with weaving, binding and other practical uses. However, specific historical uses should not automatically be attributed to Juncus edgariae where older records use the general name wīwī without precise botanical identification.

Garden value:
A tough, evergreen native rush particularly valuable for wetland, riparian and naturalistic landscaping.

The dense masses of glossy green to reddish-green stems provide strong vertical form and movement, particularly when planted in groups around ponds, streams or stormwater areas.

Its exceptional tolerance of wet ground, heavy soils, frost and exposure makes it an excellent functional restoration plant.

For smaller gardens it should be positioned carefully, as its vigorous rhizomatous growth and prolific seed production can make it invasive where conditions are favourable.