Oioi
Apodasmia similis
Apodasmia similis, commonly called oioi or jointed wire rush, is a restiad native to Aotearoa New Zealand that forms dense, wind-pollinated stands in coastal saltmarshes, estuaries and other brackish wetlands. Its segmented, rush-like culms are highly tolerant of salt, wind and periodic inundation, making oioi a mainstay of shoreline stabilization and restoration. It flowers in spring to early summer (c. Oct-Dec) with fruiting from Dec-Mar. Explore more wetland plants.
Plant Description
A tufted, rhizomatous rush up to ~1 m tall. Culms are erect, jointed and grey-green; nodes carry papery brown bracts. Leaves are reduced to sheaths at the culm bases (typical of Restionaceae). Plants are typically dioecious with separate male and female inflorescences borne near culm tips and dispersed by wind. In suitable conditions oioi forms extensive monospecific swards that baffle waves and trap sediment.
Quick Facts
| Scientific Name | Apodasmia similis |
|---|---|
| Common Names | Oioi; jointed wire rush |
| Family | Restionaceae |
| Height | 0.6-1.2 m |
| Spread | 0.6-1.0 m (clumping, slowly spreading rhizomes) |
| Water Needs | High; tolerates periodic inundation |
| Light | Full sun to light shade |
| Salt Tolerance | High (coastal, saline and brackish sites) |
| Frost Tolerance | Moderate |
| Growth Rate | Moderate |
| Lifespan | Long-lived perennial |
Climate Best Suited to
Widespread around New Zealand's coasts and lowland wetlands, including sheltered estuaries and saltmarshes in Te Ika-a-Māui (North Island), Te Waipounamu (South Island) and Rēkohu/Wharekauri (Chatham Islands). Thrives in mild, maritime climates and tolerates wind, salt spray and fluctuating water levels.
Regional Suitability
| Whangārei | Ideal |
| Auckland | Ideal |
| Hamilton | Suitable |
| Rotorua | Suitable |
| Tauranga | Ideal |
| Gisborne | Ideal |
| New Plymouth | Ideal |
| Whanganui | Ideal |
| Palmerston North | Suitable |
| Napier | Ideal |
| Wellington | Ideal |
| Nelson | Ideal |
| Christchurch | Suitable |
| Dunedin | Suitable |
| Invercargill | Suitable |
| City | Climate Suitability |
|---|
Plant Habitat
Naturally occurs in coastal wetlands, saltmarshes, lagoon margins and estuaries across much of Aotearoa New Zealand, especially on saturated, fine sediments influenced by tides and salt spray.
Plant Conservation
Widely used in restoration projects for shoreline stabilisation and stormwater treatment. Local threats include infilling of wetlands and invasive weeds; protect hydrology and control weeds for best outcomes.
Growing and Care
- Site: Full sun; wet to seasonally flooded soils (saline or brackish preferred).
- Soil: Sands, silts and peats; tolerates poor, saline and periodically anoxic substrates.
- Water: Keep moist; suitable for raingardens, swales and pond margins.
- Maintenance: Low; remove debris or trim culms to rejuvenate clumps as needed.
- Propagation: By division of rhizomes or seed; plant in groups for faster cover.
Planting Guide
Plant oioi in full sun at pond margins, raingardens, swales, and estuary edges. Group plants 40-60 cm apart to create a dense sward that traps sediments and reduces wave energy. Keep the root zone saturated during establishment.
Ecological Value
Oioi stabilises coastal wetlands, supports invertebrates and birds, and filters stormwater entering estuaries. Dense stands build organic matter, improve water clarity, and buffer shorelines from wind and waves.
Uses & Significance
Restoration & Erosion Control
Dense swards stabilise shorelines, attenuate waves and trap sediments, improving water quality and providing habitat for invertebrates and coastal birds.
Landscaping Uses
Use oioi in coastal gardens and raingardens where soils are periodically wet or saline. Combine with pāngao, spinifex, and saltmarsh herbs to create resilient, low-maintenance plantings with year-round structure.
Seasonal Notes
Spring
Active growth; flowering begins. Good time for planting and division.
Summer
Maintain soil moisture; tolerates brackish inundation.
Autumn
Fruiting; continue weed control around young plantings.
Winter
Handles storms and high tides; minimal care required.
Pruning & Training
Minimal maintenance is required. Remove storm debris and trim old culms to rejuvenate clumps if they become thatchy. Avoid heavy cutting during summer droughts.
How to Grow Oioi
Oioi thrives in full sun and waterlogged substrates and is one of the most salt-tolerant natives for coastal projects. Choose pond margins, raingardens, swales, and sheltered estuary edges where water levels fluctuate and fine sediments accumulate. Plant in groups or drifts to form a dense sward that reduces wave energy and traps sediments. Sands, silts, and peats are all suitable, but performance is best in muds and silts with regular tidal or storm-driven wetting. Avoid dry inland positions or thin, freely draining soils which can cause drought stress.
For establishment, keep the root zone saturated and weed-free through the first season. Mulch with washed sand or use biodegradable matting on slopes to stabilise sediment. In restoration, space 40-60 cm apart to quickly close canopy and capture sediment. Maintenance is minimal: remove storm debris and trim old culms if clumps become thatchy. Division of rhizomes during cooler months is straightforward and produces robust stock; ripe seed can be sown into sandy mixes and kept constantly moist for slower but useful backup supply. In brackish settings, combine oioi with Pāngao and Raupō to build layered wetlands that filter runoff and provide habitat. For coastal gardens, pairing oioi with low shrubs and sand-binders enhances wind filtration and biodiversity while maintaining a natural aesthetic.
Division
Divide established clumps in cool, moist conditions. Use a sharp spade to lift and split rhizomes with healthy culms attached, then replant divisions at the same depth and water well until re-established.
From Seed
Collect ripe seedheads, sow thinly onto a saturated sandy mix, and keep constantly moist. Prick out seedlings once they develop several culms and harden off before planting into wet sites.
Pests & Diseases
Generally robust; watch for weed competition smothering young plants, particularly aggressive grasses and weeds that establish quickly in disturbed wetland soils. Avoid prolonged drying of substrates during establishment, as drought stress makes plants vulnerable to fungal issues and weakens their natural resilience. Monitor for occasional aphid activity on new growth during warmer months, though serious pest damage is uncommon in healthy wetland environments where natural predators maintain balance.
Cultural Significance
Coastal wetlands including oioi-dominated marshes are important mahinga kai and taonga habitats, buffering coastlines and supporting biodiversity valued by many iwi and communities.
Bonus Tip
Mulch with washed sand on slopes or use biodegradable matting to stabilise sediments around new plantings. This reduces erosion and accelerates canopy closure.
Related Plants
Other salt-tolerant coastal plants that thrive alongside oioi and help stabilise dunes, marshes, and estuary edges.
