Tall Spike Sedge

Botanical name: Eleocharis sphacelata
Synonyms: None
Common name(s): Kuta, Kutakuta, Pāopāo, Tall Spike Sedge, Bamboo Spike Sedge, Giant Spike-rush, Spikes of Doom

About:
Eleocharis sphacelata is a large, robust aquatic sedge distinguished by its tall, hollow, bamboo-like stems. These stems contain regular internal cross-partitions which can often be felt or seen as distinct nodes along their length.

The plant spreads through stout creeping rhizomes and forms dense colonies in still or slowly moving freshwater. It is among New Zealand’s tallest native spike-sedges and is especially characteristic of lakes, ponds, swamps and raupō wetlands.

Natural habitat:
Occurs from coastal wetlands to lower montane areas, although it is most common in lowland freshwater habitats.

It usually grows in full sun in still or slow-moving water along lake margins, ponds, lagoons, swamps and wetland pools. It may also occur beside slow-flowing streams and rivers, in peat-bog depressions and in pools formed after fire.

Plants often grow among raupō and jointed twig rush, with their rhizomes permanently submerged beneath the water.

Growing environment:
Requires permanently wet ground or standing freshwater. It grows best where its rhizomes remain submerged in soft mud, peat or organic sediment.

Full sun encourages dense growth and flowering. The species tolerates deep water and fluctuating water levels, but it is not suited to ordinary dry garden soil.

Endemic distribution:
Indigenous to New Zealand but not endemic. It occurs in suitable freshwater wetlands across the country.

It is also native to Australia, New Guinea, New Caledonia and nearby regions of the south-west Pacific.

Height:
Usually 0.3–1.2 m above the water, but stems may become considerably taller in deep or sheltered habitats

Width:
Forms large spreading colonies through creeping rhizomes

Flowering:
August–December

Fruiting:
November–May

Uses:
• Freshwater wetland restoration
• Lake and pond margins
• Wildlife habitat
• Waterway and shoreline stabilisation
• Naturalistic aquatic planting
• Traditional weaving
• Tukutuku panels
• Cultural and educational planting

Appearance:
Growth habit:
A perennial aquatic sedge forming dense stands of upright, closely packed stems arising from a spreading underground rhizome system.

Colonies may expand over wide areas where water depth and sediment conditions are suitable.

Rhizomes:
The rhizomes are stout, woody and creeping, generally 10–15 mm in diameter. They grow through submerged sediment and produce new groups of stems at intervals.

Roots:
Roots are thick, reddish brown and approximately 2 mm in diameter. Several roots arise together from the base of each stem and anchor the plant firmly into wetland mud.

Stems:
The stems, known botanically as culms, are cylindrical, soft, hollow and generally 4–12 mm wide. They are green to yellow-green and usually tightly clustered.

Regular transverse partitions occur within each hollow stem, commonly at intervals of 1–10 cm. These internal septa give the stems their characteristic bamboo-like structure.

Sterile stems usually have blunt or rounded tips, while fertile stems end in a conspicuous spikelet.

Leaves:
Functional leaf blades are absent. The foliage is reduced to greyish, papery basal sheaths surrounding the lower portions of the stems.

The upright green culms carry out photosynthesis.

Flowers:
The tiny flowers are densely packed into a single cylindrical spikelet at the top of each fertile stem.

Spikelets are approximately 20–70 mm long and 5–10 mm wide, with a sharply pointed tip. They are composed of numerous overlapping brown glumes, each with a strong central vein and several finer lateral veins.

Individual flowers are inconspicuous and wind pollinated.

Fruit:
The fruit is a small, pale brown nut approximately 2–2.5 mm long. It is broadly rounded, slightly flattened and marked with a distinctive network of hexagonal surface patterns.

A dark brown, cone-shaped remnant of the style remains attached to the top of the mature nut.

Seeds:
Each nut contains a single seed and is surrounded by six to ten bristles. The bristles bear backward-pointing teeth and assist movement by water or attachment to animals.

Ecology:
Kuta is an obligate wetland plant and is almost entirely restricted to aquatic or permanently saturated habitats.

Its dense rhizome network binds soft sediment and helps stabilise lake and pond margins. Large stands reduce wave action, trap suspended material and create sheltered areas for aquatic organisms.

The hollow stems provide cover for insects, fish, waterfowl and other wetland animals. Dense colonies may also offer nesting and feeding habitat for native birds.

Its ability to transport air through hollow, partitioned culms allows the submerged rhizomes and roots to survive in oxygen-poor wetland soils.

Associated habitats:
Freshwater lakes, ponds, lagoons, swamps, marshes, slow-moving streams, river margins, peat-bog pools and permanently flooded depressions.

Associated species commonly include raupō, jointed twig rush, sharp spike sedge, giant umbrella sedge, oioi, swamp millet and other native sedges, rushes and aquatic plants.

How to grow:
Plant into soft mud or saturated soil with the rhizomes permanently submerged. It may be established around pond margins or in large aquatic containers placed below the water surface.

Choose a sunny position with still or slowly moving freshwater. The plant needs considerable space because its rhizomes spread steadily and may form large colonies.

Once established, little maintenance is required. Old stems may be removed if necessary, although they normally break down naturally within the wetland.

Propagation:
Division of established plants is the most practical method. Lift sections of rhizome with healthy roots and several live stems attached, then replant immediately into submerged mud.

Propagation from fresh seed is possible but can be difficult. Mature nuts may be floated on shallow water above a container of wet potting mix or fine sediment.

As germination begins, gradually lower the water level so the seedlings settle naturally onto the growing medium. Young plants should remain wet or partly submerged throughout establishment.

Cultural use:
The long, lightweight stems of kuta were traditionally harvested, dried and used by Māori for weaving. They were made into soft mats, sleeping coverings and other woven items, and were also incorporated into tukutuku panels.

The stems were valued because they became light, flexible and insulating after careful harvesting and drying. In some areas, particularly where the plant was abundant, highly skilled weavers became known for producing fine kuta or pāopāo mats.

Kuta remains culturally important as a material used in raranga and as a living component of traditional wetland landscapes.

Garden value:
Kuta is an impressive native aquatic plant for large ponds, lake margins, wetland restorations and naturalistic water gardens. Its tall, clean stems create strong vertical form and gentle movement above the water.

It is most suitable for spacious sites where its spreading habit can be accommodated. Beyond its visual appeal, it contributes valuable habitat, shoreline protection and cultural significance to freshwater plantings.