Giant Rush
Botanical name: Juncus pallidus
Synonyms: Juncus macrostigma, Agathryon pallidum
Common name(s): Giant rush, wīwī, leafless rush
About:
A very large, robust perennial rush forming dense stands of tall, erect, blue-green to pale glaucous stems. Juncus pallidus is one of New Zealand’s most imposing native rushes, commonly reaching 2 m tall and spreading through strong horizontal rhizomes.
It is primarily a plant of coastal and lowland wetlands, damp pasture, swampy hollows and lake margins. Its vigorous rhizomatous growth makes it particularly effective at colonising and stabilising wet ground, although the same characteristic can make it troublesome in pasture.
Its tall stature and attractive blue-grey foliage give it considerable value for wetland restoration and large-scale naturalistic landscaping.
Natural habitat:
Coastal to lowland.
Typically found in damp swampy hollows, wet pasture, lake and wetland margins, riparian areas, open shrubland on damp ground and the wetter parts of coastal dune systems.
It also occurs near saltmarshes in slightly elevated positions that may be periodically flooded during exceptionally high or king tides.
Growing environment:
Full Sun, Partial Shade, Wet Soil, Heavy Soil, Standing Water, Coastal Exposure, Wind, Frost & Periodic Drought tolerant.
It performs best in full sun and consistently damp to wet ground but is remarkably adaptable once established.
Endemic distribution:
Indigenous but not endemic to New Zealand.
Naturally occurs in the North Island, South Island and Stewart Island/Rakiura.
Also indigenous to Australia. It is naturalised on Norfolk Island, Lord Howe Island and the Chatham Islands.
Height:
1–2 m.
Width:
Approximately 60 cm–1.5 m or more per established clump. Through rhizomatous spread, mature colonies can eventually occupy substantially larger areas.
Flowering:
October–January.
Produces numerous small pale green to occasionally pink-tinged flowers in an apparently lateral inflorescence.
The inflorescence may form a dense head more than 15 mm across or develop into a larger, open structure with long, stout branches.
Fruiting:
November–May.
Produces pale greenish-brown capsules approximately 2.8–3.6 mm long, usually conspicuously longer than the surrounding tepals.
Uses:
• Wetland restoration
• Riparian revegetation
• Pond and lake margins
• Stream and river margins
• Stormwater systems
• Rain gardens and swales
• Constructed wetlands
• Erosion control
• Bank stabilisation
• Coastal revegetation
• Wildlife habitat
• Screening
• Large-scale naturalistic landscaping
Its large size and vigorous spreading habit should be considered carefully when planting near pasture or within small gardens.
Appearance:
Growth habit:
A very robust, evergreen, rhizomatous perennial rush forming dense patches of strongly upright stems.
The horizontal rhizome is approximately 5–10 mm in diameter and enables established plants to gradually spread into substantial colonies.
Its tall, strongly vertical growth makes it considerably more imposing than many other native Juncus species.
Leaves:
True leaves are absent.
The photosynthetic flowering stems form the conspicuous blue-green foliage of the plant.
Numerous basal sheathing bracts surround the stems. The lower bracts are shorter while the upper ones become larger and more loosely sheathing.
The upper bracts are characteristically very blunt but terminate in a long, fine, hair-like point. Their colour ranges from pale green to light brown or pinkish-brown.
Flowers:
Flowering stems are approximately 1–2 m tall and 3–8 mm in diameter.
They are erect, smooth, soft and slightly glossy, usually light green to distinctly glaucous or blue-green.
A particularly useful identification feature is the internal pith, which is continuous rather than interrupted.
The apparently lateral inflorescence is many-flowered and highly variable. It may be contracted into a dense head more than 15 mm across or become open and spreading with long, stout, rigid branchlets.
Individual flowers are approximately 2.3–3 mm long and may occur in clusters at the branchlet tips or be more evenly distributed along them.
The six tepals are initially pale green and sometimes tinged pink, becoming light brown with age. The outer tepals are comparatively rigid while the inner tepals are soft, membranous and almost colourless.
Each flower has six stamens.
Fruit:
Capsules are approximately 2.8–3.6 mm long and usually distinctly longer than the tepals.
They are ovoid-trigonous, blunt at the apex and characteristically very pale greenish-brown.
The numerous small mucilaginous seeds may be dispersed by water, wind and attachment to animals.
Ecology:
Juncus pallidus is an important structural species of wetland margins and other periodically saturated environments.
Its dense rhizome network binds wet and unstable substrates, helping reduce erosion and consolidate the margins of wetlands, streams, ponds and drainage systems.
The tall stems create dense vertical cover and contribute shelter and habitat complexity for wetland invertebrates and other fauna.
Although predominantly associated with wetlands, it can withstand periods of considerably drier conditions once established. This combination of tolerance to saturation and temporary drought makes it particularly useful where water levels fluctuate seasonally.
Its ability to spread vigorously also allows it to rapidly occupy disturbed wet ground.
Associated habitats:
Freshwater wetlands, swampy hollows, lake margins, pond margins, stream banks, riparian zones, wet pasture, coastal dune wetlands, open damp shrubland, saltmarsh margins and periodically inundated coastal flats.
Common associated native plants can include Apodasmia similis, Carex maorica, Carex secta, Carex virgata, Eleocharis acuta and Phormium tenax.
How to grow:
Very easy to establish and extremely hardy.
Plant in full sun for the strongest, most upright growth, although moderate shade is tolerated.
It performs particularly well in damp to permanently wet soil and can tolerate standing water, heavy soils and poorly drained ground. Once established, plants are also surprisingly tolerant of heat and temporary drought.
For wetland restoration, allow adequate spacing for plants to develop into substantial tussocks and eventually spread through their rhizomes.
In smaller gardens, consider containing the root system or removing flowering stems before seed matures if uncontrolled spread is undesirable.
Propagation:
Easily propagated from fresh seed and division.
Surface-sow fresh seed onto consistently moist propagation media. Maintain moisture throughout germination and early establishment.
Established plants can be divided by separating sections of rhizome carrying healthy stems and roots. Divisions can be planted directly into suitably damp ground and generally establish readily.
Cultural use:
Wīwī is a Māori name used for several indigenous rushes and similar wetland plants.
Native rushes formed part of the traditional fibre resources of Aotearoa and were associated with practical uses such as weaving, binding and construction. However, where historical accounts refer simply to wīwī, those uses cannot always be confidently assigned specifically to Juncus pallidus.
Today the species remains an important component of indigenous wetland and riparian vegetation.
Garden value:
An impressive architectural native rush particularly suited to larger gardens, ponds, wetlands and restoration landscapes.
Its tall, pale blue-green to glaucous stems form strong vertical masses and provide excellent contrast against darker foliage, flax, sedges and lower-growing wetland plants.
It is especially useful where a large, hardy native is required to provide height, screening and rapid coverage of wet ground.
Because Juncus pallidus can reach 2 m tall and spread vigorously through both rhizomes and seed, it is best given plenty of space. In the right setting, however, it is one of the most striking native rushes for large-scale wetland and riparian planting.