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Machaerina

Machaerina arthrophylla

Not Threatened

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Baumea arthrophylla, now called Machaerina arthrophylla, is a native wetland sedge with slender, cylindrical, rush-like stems 0.5-1.3 m tall. Its upper leaves are terete and divided inside by cross-walls, giving the jointed appearance its name refers to. Loose, interrupted panicles of small brownish spikelets appear from October to December. It grows from the coast to 1200 m on lake and tarn margins, along slow streams and in burn pools within restiad bogs, from Waikato south to Southland and on the Chatham Islands. It also occurs in Australia, is Not Threatened, and is slow to establish in cultivation. Explore more native grasses and flaxes in our native plant guide.

Machaerina (Machaerina arthrophylla) in its natural habitat
Image credit: Machaerina (Machaerina arthrophylla) - photo by Wikipedia contributors, via Wikipedia

Plant Description

Machaerina arthrophylla is a dark green, rhizomatous sedge. Its rhizome is about 3 mm in diameter, horizontal, shortly creeping, hard and woody, and clothed in loose bracts. The culms (stems) are 0.5-1.3 m tall, only 1-2 mm thick and terete (round in cross-section).

The upper one to three leaves are also terete, like the stems, with acute tips. They are internally septate, meaning they have cross-walls inside at intervals, which can often be felt as slight joints when the leaf is run between the fingers. The flower head is a panicle 100-400 mm long, rounded at the tip and interrupted, with drooping branchlets and light greenish-brown bracts. The spikelets are 3-4.5 mm long with two to four flowers, usually only the lowest two fertile.

It is closely similar to Machaerina rubiginosa, which also has terete septate leaves but usually has somewhat larger (4.5-6 mm), rusty red-brown spikelets and pale or orange-yellow nuts. Careful examination of spikelets is the safest way to separate them.

Quick Facts

Machaerina arthrophylla quick facts
Scientific Name Machaerina arthrophylla
Height 0.5-1.3 m
Spread Slowly creeping clumps from a short rhizome
Water Needs High; permanently wet ground or shallow water
Light Full sun
Frost Tolerance Hardy; grows to subalpine altitudes
Salt Tolerance Low; a freshwater wetland plant
Growth Rate Slow
Lifespan Perennial

Climate Best Suited to

Grows from warm lowland to cold subalpine climates in the central and southern North Island, the South Island and the Chatham Islands, provided the ground stays permanently wet.

Regional Suitability

City suitability for Machaerina arthrophylla
City Climate Suitability
Auckland Medium
Wellington High
Christchurch Medium
Dunedin High

Plant Habitat

This sedge is indigenous to New Zealand and Australia. In the North Island it is found from Waikato south to Waiouru, in the South Island on D'Urville Island, in Westland and in Southland, and it also grows on the Chatham Islands. It is regionally uncommon in Auckland and Wellington.

It grows from the coast to the subalpine zone at up to 1200 m, in freshwater wetlands, especially on the margins of lakes, tarns and slow-flowing streams. It also colonises burn pools within restiad bogs, the peat bogs dominated by wire rush and jointed rushes. It is classed as an obligate wetland plant, almost always found in wetlands.

Growing Requirements

Soil Requirements

It needs permanently saturated soils, typically peat or wet mineral silt at the edges of open water.

  • Waterlogged peat or silty margins
  • Acidic bog soils are well tolerated
  • Low fertility is fine

Light Requirements

This is a plant of open wetlands and lake edges, where it receives full sun.

  • Full sun
  • Tolerates light shade from neighbouring sedges
  • Avoid deeply shaded sites

Water Requirements

As an obligate wetland plant it must have constantly wet roots, and it grows naturally at the edge of standing water.

  • Permanently wet soil or shallow water
  • Lake, tarn and pond margins
  • Not drought tolerant

Planting and Establishing

Plant into permanently wet ground at the margin of a pond or wetland restoration site. Because NZPCN notes that it resents root disturbance, use plants grown in deep containers and plant them with the root ball intact.

Plant in spring so that young plants have a full growing season to settle in, and keep surrounding weeds down while it slowly establishes.

Ecological Role

Like other sedges it is wind pollinated, and its nuts are wind dispersed. Its tall, slender stems add vertical structure to lake-edge vegetation and provide cover for wetland invertebrates and birds.

In restiad bogs it colonises burn pools, the hollows left after peat fires, making it part of the natural recovery of bogs after disturbance.

Uses & Significance

Garden Uses

It is mainly a plant for wetland restoration within its natural range, rather than general garden use, because of its slow establishment.

  • Wetland and lake-margin restoration
  • Natural pond edges
  • Bog gardens with permanently wet peat

Ecological Value

As an obligate wetland sedge, it is part of the native vegetation of lake margins and peat bogs, ecosystems that have been greatly reduced in New Zealand.

  • Structural cover at water margins
  • Colonises burn pools in restiad bogs
  • Supports wetland invertebrates

Landscaping Uses

Use it in drifts along the shallow edge of a natural pond, where its fine, upright stems and drooping brownish panicles create a soft vertical texture against open water.

It mixes well with other native wetland plants of similar habitats such as other Machaerina species and native rushes.

Seasonal Care Calendar

Spring

Flowering begins in October, with loose panicles rising above the stems through to December.

  • Plant out new stock
  • Weed around young plants

Summer

Fruiting starts in December. Water levels must stay high enough to keep the roots wet.

  • Top up garden ponds in dry spells
  • Begin collecting ripe nuts

Autumn

Nuts continue to ripen until May and are dispersed by wind.

  • Sow fresh seed
  • Leave seed heads for natural dispersal

Winter

Growth slows in cold months, but the evergreen stems remain standing.

  • No action needed
  • Avoid trampling wet margins

When to Prune and How Much

No pruning is required. Old, dead stems can be cut out at the base in late winter if a clump becomes untidy.

Avoid cutting the whole clump to the ground, which slows recovery in this slow-growing sedge.

How to Grow Machaerina

NZPCN describes propagation of Machaerina arthrophylla as difficult. It can be grown from fresh seed but is slow to establish, and it resents root disturbance, so division is risky and container-grown plants should be handled carefully. Fruiting runs from December to May, giving a long season for collecting ripe nuts. Because it is regionally uncommon in Auckland and Wellington, eco-sourced seed from the local area is best for restoration plantings, collected with landowner permission and without stripping wild plants.

From Seed

Fresh seed is the most reliable method, but seedlings grow slowly and may take a couple of seasons to reach planting size.

  1. Collect ripe nuts between December and May
  2. Sow fresh onto a moist peat-based or sandy seed mix
  3. Stand the tray in a saucer of water so the mix stays wet
  4. Prick out seedlings carefully into deep pots, handling them by the leaves and disturbing the roots as little as possible
  5. Grow on in full sun with constantly wet roots until well established

By Division

Division is possible because the plant has a short creeping rhizome, but because it resents root disturbance success is variable and divisions should be large.

  1. Divide in spring when growth resumes
  2. Cut large sections with several stems and plenty of rhizome
  3. Pot into a wet, peaty mix and keep standing in water
  4. Allow a full growing season for the division to re-establish before planting it out, and expect some losses

Pests & Diseases

No specific pests or diseases are recorded for this species in the sources consulted.

The main risks are drainage of wetlands, falling water levels and competition from invasive wetland weeds that can overgrow slow-establishing sedges.

Cultural Significance

No Māori name or traditional use is recorded for this species in the sources consulted.

The epithet arthrophylla means jointed leaf, from the Greek arthron (joint) and phyllon (leaf), referring to the internal cross-walls in its leaves. It was described by Nees and later transferred to Baumea by Boeckeler and to Machaerina by Koyama.

Bonus Tip

To confirm you have a septate-leaved twig rush, pinch a leaf and slide your fingers along it, or slit one lengthwise: you will see or feel the regular internal cross-walls. Then check the spikelet size and colour to tell M. arthrophylla from M. rubiginosa.

Plant Conservation

Machaerina arthrophylla is ranked Not Threatened nationally (2023) with the qualifier Secure Overseas. Regionally it is At Risk - Naturally Uncommon in Auckland and Wellington, and Not Threatened in Northland.

Loss and drainage of lake-margin wetlands and peat bogs are the main pressures. Protecting wetlands, maintaining natural water levels and controlling weeds help this and other wetland sedges.

Frequently Asked Questions

What is the current name for Machaerina arthrophylla?

It is now Machaerina arthrophylla. New Zealand was among the last places to use Baumea, and NZ botanists have since adopted Machaerina for these twig rushes.

Where does Machaerina arthrophylla grow in New Zealand?

In the North Island from Waikato south to Waiouru, in the South Island on D'Urville Island, Westland and Southland, and on the Chatham Islands, in freshwater wetlands up to 1200 m.

Is Machaerina arthrophylla easy to grow?

No. NZPCN describes it as difficult: it can be grown from fresh seed but is slow to establish and resents root disturbance.

Sources and Further Reading

The botanical, growing, and conservation details for Machaerina (Machaerina arthrophylla) on this page draw on the New Zealand plant references below. Consult them for full technical records and the latest distribution data.