Square-stemmed Sedge

Botanical name: Lepidosperma australe
Synonyms: Vauthiera australis, Cladium vauthiera, Cladium australe, Machaerina australis
Common name(s): Square sedge, Square-stemmed sedge

About:
A distinctive, robust New Zealand sedge forming dense, upright patches of striking blue-green to dark green stems. Unlike most sedges, Lepidosperma australe has its leaves largely reduced to brown basal sheaths, leaving the rigid, four-angled stems to perform much of the plant’s photosynthesis.

The square stems are its most useful identifying feature and give rise to both common names. Plants can range from relatively compact colonies in exposed sites to imposing stands approaching 2 m tall in favourable conditions.

It is remarkably adaptable in the wild, occurring from coastal environments to alpine areas and inhabiting both well-drained, seasonally dry ground and permanently wet peatlands.

Natural habitat:
Coastal to alpine, from near sea level to approximately 1,300 m elevation.

It occurs predominantly in open ground, peat bogs, wetlands, scrub margins and seral or regenerating vegetation. It is unusual in its ability to colonise both seasonally dry or freely drained substrates and permanently wet peat.

Plants may form conspicuous dense colonies where conditions are suitable.

Growing environment:
Highly adaptable once established, growing in full sun to shade and in soils ranging from freely draining to permanently damp.

It performs particularly well in open, moist sites but established plants can tolerate considerable variation in moisture availability. It is hardy to frost, exposure and the cool conditions characteristic of upland and alpine environments.

Although mature plants are resilient, establishment can be difficult because the root system resents disturbance.

Endemic distribution:
Endemic to New Zealand.

North Island, South Island, Stewart Island/Rakiura and Chatham Islands.

It has an exceptionally broad ecological and geographical range, extending from coastal environments through lowland and montane habitats to alpine areas.

Height:
20 cm–2 m

Width:
Approximately 30 cm–1 m+, gradually expanding into dense patches

Flowering:
August–December

Flowers are inconspicuous overall, although the elongated red anther connectives can provide noticeable reddish colouring to flowering plants.

Fruiting:
October–July; mature fruits may remain present throughout much of the year

Uses:
• Native wetland planting
• Bog and peatland restoration
• Riparian planting
• Revegetation projects
• Naturalistic landscaping
• Rain gardens and damp areas
• Rock and gravel gardens where moisture is available
• Architectural accent planting
• Specialist native plant collections
• Restoration of ultramafic vegetation
• Habitat and biodiversity planting

Appearance:
Growth habit:
A stout, rush-like perennial sedge growing from short, woody rhizomes approximately 2–3 mm in diameter.

Numerous rigid stems arise closely together to form dense, strongly upright patches. Older colonies can develop into substantial stands with a distinctive architectural appearance.

The rhizomes bear spaced, dark brown, pointed scales.

Leaves:
Most leaves are greatly reduced and appear as brown, membranous, sheathing bracts around the stems.

The upper one or two leaves may occasionally develop proper blades approximately 5–35 cm long. These are usually four-angled like the stems, although occasionally triangular in cross-section.

Their tips taper into sharp, rigid, dark brown points.

Because the leaves are so reduced, the upright green stems form the dominant visible foliage of the plant.

Stems:
The culms are approximately 20 cm–2 m tall and 1–2.5 mm in diameter.

They are densely packed, rigidly erect, hairless and leathery, with a characteristic dark blue-green, grey-green or glaucous colour.

Most importantly, each stem is distinctly quadrangular or square in cross-section. This feature readily distinguishes Lepidosperma australe from other superficially similar native sedges and rushes.

Flowers:
Flowers are contained within dense, narrow, spike-like heads approximately 10–40 mm long and 5–15 mm wide.

Individual spikelets are approximately 4–5 mm long, single-flowered and carried on short, stout stalks.

Each spikelet has four to six tough glumes. The lower glumes are empty, with only the uppermost glume fertile.

The glumes are brownish, leathery and finely roughened, with a prominently thickened midrib.

The anthers have conspicuous elongated red connectives, accounting for the reddish-pink appearance sometimes visible during flowering.

Fruit:
The fruit is a smooth, glossy, light-brown nut approximately 4 mm long.

It is oblong to ellipsoid and more or less three-angled, narrowing toward the persistent roughened style base.

Six small white scales occur around the base of the mature nut. These become joined at their bases to form a persistent six-lobed cup.

Seeds:
The nut-like fruits are dispersed by a combination of water and wind, while ants may also contribute to their movement.

The species’ ability to occupy both wetlands and relatively dry open habitats means dispersal mechanisms vary considerably between populations.

Ecology:
Lepidosperma australe is an ecologically versatile sedge associated with both wetlands and upland vegetation.

Its wetland indicator status is Facultative (FAC), reflecting its ability to occur commonly in either wetland or non-wetland environments.

Dense colonies provide low-level cover and structure for invertebrates and other small fauna while helping protect exposed soil and peat surfaces.

It is also an important component of some specialised mineral-soil vegetation. In the Nelson region it occurs in ultramafic landscapes, including shrubland communities associated with mānuka (Leptospermum scoparium) and specialised species such as Ultramafic Gentian (Gentianella stellata).

Its broad environmental tolerance contrasts strongly with the difficulty sometimes encountered when attempting to transplant or propagate it.

Associated habitats:
Peat bogs, wetlands, coastal vegetation, open ground, regenerating vegetation, scrub margins, montane shrublands, alpine vegetation, seasonally dry ground, permanently damp soils and ultramafic landscapes.

Associated species vary greatly with location. In Nelson’s ultramafic areas it may occur with mānuka (Leptospermum scoparium), Gentianella stellata and other plants adapted to the distinctive mineral-rich substrates of Dun Mountain and the Richmond–Bryant ranges.

How to grow:
Despite its adaptability in the wild, Square-stemmed Sedge can be surprisingly difficult to establish in cultivation.

Plants strongly resent root disturbance. Established wild plants generally transplant poorly and may die following disturbance, so established specimens should not be removed from natural populations.

Nursery-grown plants should be planted with the root ball kept as intact as possible. Avoid teasing apart or unnecessarily disturbing the roots.

Once established, the species is much easier to maintain. It can flourish in full sun or shade and will tolerate conditions ranging from freely draining soil to permanently damp ground.

A low-fertility, humus-rich or mineral-based substrate is suitable, depending on the intended planting environment. Maintain reliable moisture during establishment.

It is particularly suited to naturalistic wetland plantings, damp native gardens and specialised ecological restoration where its unusual upright form can be appreciated.

Propagation:
Propagation from seed can be difficult and germination may be slow or unreliable.

Interestingly, considerable success has been reported using untreated sawdust as a propagation medium, both for germinating seed and establishing young plants.

Fresh mature fruits should be collected and sown into a moist, open medium. Maintain consistent moisture without creating stagnant conditions and allow natural seasonal temperature changes.

Division is theoretically possible because plants spread by short rhizomes, but disturbance of established root systems carries a substantial risk of plant loss and should be approached cautiously.

Propagation from nursery-grown material is preferable to disturbing wild colonies.

Cultural use:
No specific traditional Māori uses are widely documented for Lepidosperma australe.

The species nevertheless contributes to a wide variety of indigenous ecosystems throughout Aotearoa, from coastal and wetland environments to some of the country’s distinctive alpine and ultramafic plant communities.

The genus name Lepidosperma refers to the scale-like structures associated with the fruit, while the specific name australe means southern.

Garden value:
An unusual and highly architectural native sedge deserving wider use in specialist native gardens.

Its tightly packed, rigid, square stems create a strong vertical texture quite unlike conventional leafy sedges. The blue-green to grey-green colouring is particularly attractive when planted amongst lower groundcovers, rocks or wetland vegetation.

It is especially useful where a natural transition is required between damp and relatively dry planting zones because established plants tolerate a remarkably broad range of moisture conditions.

For Nelson–Tasman gardens and ecological plantings, it has additional regional interest because of its occurrence within the distinctive ultramafic vegetation associated with Dun Mountain and the Richmond–Bryant ranges.

The main limitation is establishment rather than long-term performance. Once successfully established without significant root disturbance, Lepidosperma australe can develop into a robust, long-lived and visually distinctive native feature.