Bolboschoenus caldwellii

Botanical name: Bolboschoenus caldwellii
Synonyms: Scirpus caldwellii
Common name(s): Purua Grass, Caldwell’s Clubrush, Marsh Club Rush

About:
A robust rhizomatous wetland sedge native to New Zealand and Australia. This species forms dense clumps in saltmarshes, estuaries, wetlands, and damp coastal depressions, where it helps stabilise soft soils and provide habitat for wetland wildlife.

Natural habitat:
Saltmarshes, estuarine margins, tidal creeks, swamps, poorly drained saline flats, and lowland wetlands.

Growing environment:
Full sun to partial shade, Wet soils, Brackish wetlands, Pond margins, Coastal marshes, Damp lowland sites.

Endemic distribution:
Indigenous to New Zealand. Found in the North Island from Kaipara Harbour southwards, mainly in eastern districts, and throughout much of the eastern South Island from Nelson to Otago. Also native to Australia.

Height:
0.3–1 m tall

Width:
Forms spreading colonies via rhizomes

Flowering:
October–January

Fruiting:
December–May

Uses:

• Wetland restoration
• Saltmarsh revegetation
• Pond and stream margins
• Erosion control
• Wildlife habitat
• Traditional food source

Appearance:

Growth habit:
A summer-green perennial sedge forming dense clumps from creeping underground rhizomes with woody tubers.

Stems:
Upright triangular culms arising from underground tubers.

Leaves:
Long narrow grass-like leaves, folded and tapering, pale to mid green, often slightly glaucous with rough margins near the tips.

Flowers:
Compact terminal clusters of reddish-brown to golden-brown spikelets held at the tops of the stems.

Fruit:
Glossy cream to dull-brown nuts with fine bristles adapted for dispersal by water.

Ecology:
An important coastal wetland species that stabilises muddy estuarine soils and provides habitat for wetland birds, aquatic insects, and amphibians.

Associated habitats:
Often found with oioi, sea rush, jointed rush, glasswort, and other estuarine and saltmarsh vegetation.

How to grow:
Thrives in permanently damp to shallowly flooded soils and tolerates brackish conditions, inundation, and frost. Best planted in full sun.

Propagation:
Easily grown from fresh seed or by division of rooted rhizomes and tubers.

Threats:
Not threatened, though uncommon in the northern part of its range.

Cultural significance:
The underground tubers were traditionally eaten by Indigenous communities in Australia.

Garden value:
Excellent for wetland gardens, pond margins, rain gardens, estuarine restoration, and naturalistic aquatic plantings where its upright foliage provides texture and structure year-round.