Heart Leaf Kōhūhū
Pittosporum obcordatum
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Pittosporum obcordatum is a threatened shrub to small tree with characteristic obcordate (notched) leaf tips. It persists in lowland forests and riparian margins and benefits from targeted site protection.
Identification
Small, opposite leaves with distinctive notched (obcordate) tips; small flowers and sticky-seeded capsules. Compare with P. tenuifolium and related species by leaf shape and fruit characters.
Quick Facts
| Scientific Name | Pittosporum obcordatum |
|---|---|
| Family | Pittosporaceae |
| Threat Status | Nationally Endangered |
| Height | 2-8 m (varies with site) |
| Spread | 40-120 cm across |
| Water Needs | Moderate; avoid waterlogging |
| Light | Bright shade to dappled light |
| Frost Tolerance | Moderate |
| Salt Tolerance | Low to moderate |
| Growth Rate | Slow to moderate |
| Lifespan | Long-lived perennial |
Climate Best Suited to
Mild, frost-free microclimates; shelter from cold, desiccating winds.
Regional Suitability
| City | Suitability |
|---|---|
| Auckland | Ideal |
| Hamilton | Ideal |
| Wellington | Ideal |
| Whangārei | Suitable |
| Tauranga | Suitable |
| Rotorua | Suitable |
| Gisborne | Suitable |
| New Plymouth | Suitable |
| Napier | Suitable |
| Whanganui | Suitable |
| Palmerston North | Suitable |
| Nelson | Suitable |
| Christchurch | Suitable |
| Dunedin | Suitable |
| Invercargill | Suitable |
Habitat
Natural Distribution
A species of fertile river flats and lowland forests, Pittosporum obcordatum was formerly scattered through alluvial terrace forests, floodplain margins and well‑drained toe slopes where seasonal groundwater pulses were buffered by deep soils. It persists today as small, discontinuous populations in remnant kahikatea-mataī-tōtara forest and mixed swamp forest edges, often with divaricating shrubs and ribbonwood. Plants favour warm, sheltered microsites with even soil moisture but dislike chronic waterlogging. This ecological preference explains the species’ sensitivity to river engineering, drainage, and loss of riparian forest structure across its historic range.
Conservation Status
Current Threats and Protection
Classified as Nationally Endangered, the species has declined through habitat loss, drainage of floodplain forests, selective browsing, and weed ingress along waterways. Many stands are small and isolated, making them vulnerable to stochastic events and inbreeding in this dioecious plant. Priority actions include protecting and expanding riparian forest remnants, excluding stock and browsers, controlling invasive vines and tall herbs, and augmenting small populations with eco‑sourced plants to improve sex ratios and genetic diversity. Securing natural river margin dynamics-periodic disturbance without wholesale channelisation-supports recruitment niches.
How to Grow
Cultivation Requirements
Provide humus‑rich, free‑draining loams in bright shade to light woodland sun, sheltered from hot, desiccating winds. Maintain steady moisture through dry spells but avoid soggy roots; raised beds or bermed planting holes help on heavier soils. Juveniles benefit from a light, open canopy and weed‑free root run; once established they tolerate moderate frost if well mulched. Avoid high‑nitrogen fertilisers which push soft growth attractive to sap‑suckers.
Planting Guide
Best Planting Practices
Choose eco‑sourced stock from the same catchment where possible. Plant in late autumn or early spring into well‑prepared, weed‑free ground; incorporate leaf mould and coarse fines to mimic forest soils. Staggered groupings under taller nurse species create the filtered light and shelter this pittosporum prefers. Water deeply after planting, stake only if exposure is severe, and mulch with woodchips while keeping the stem base free.
Ecology
As an understorey small tree, P. obcordatum adds vertical structure and fine‑scale complexity to remnant lowland forest. The small, scented flowers provide seasonal resources for insects, while the sticky‐coated seeds are dispersed by birds and gravity. Dense branch networks create shelter and perches for invertebrates and small birds, particularly where divaricating shrubs have declined from browsing.
Uses
Traditional and Modern Applications
Best suited to restoration and sanctuary plantings that recreate lowland river terrace forest. In larger gardens it forms a handsome, fine‑textured small tree for woodland edges and sheltered courtyards. Its rarity means it should be prioritised for conservation‑led horticulture rather than mass amenity use.
Landscaping Ideas
In larger gardens, site P. obcordatum beneath open‑canopied tōtara, lacebark or kōwhai to emulate filtered woodland light. Combine with divaricating shrubs, ground ferns and leaf‑littered paths to suggest the texture of lowland terrace forest. Avoid cramped beds or clipped hedging-this is a small forest tree best shown with an airy frame and an undisturbed root zone.
Seasonal Care
Year-Round Maintenance
In spring, top up mulch and check stakes and ties. Through summer dry spells, soak infrequently but thoroughly to encourage deep rooting. In autumn, remove weeds encroaching on the root zone and refresh mulch. In colder districts, protect first‑year plants from radiative frosts with breathable covers on clear nights.
Pruning
Pruning Techniques
Prune lightly after flowering to remove dead or crossing wood and maintain a single or multi‑stem framework. Avoid hard renovation cuts-like many pittosporums, this species resents severe pruning and can be slow to reshoot.
How to Grow Heart Leaf Kōhūhū
From Seed
Propagation of Pittosporum obcordatum from fresh seed is a viable method, crucial for its conservation. Collect seeds from ripe capsules in late autumn or early winter, once they begin to split open. Clean the sticky pulp from the seeds thoroughly. The resinous seed coat can inhibit water uptake, so gentle scarification (e.g., light abrasion with sandpaper) can improve results. Sow scarified seeds in late winter to spring onto a humus-rich, free-draining seed-raising mix, lightly covering them. Maintain consistent moisture and provide warm temperatures (around 18-25°C or 65-77°F) for optimal germination. Germination can be erratic and sometimes slow. Once seedlings are robust enough to handle, prick them out into individual pots and grow them on in light shade with even moisture until strong enough for planting out.
From Cuttings
Pittosporum obcordatum can be successfully propagated from semi-hardwood cuttings taken in late summer to early autumn. Select healthy, firm stem segments, about 10-15 cm long, from the current season's growth. Remove the lower leaves and dip the cut end in a rooting hormone to encourage root development. Insert the cuttings into a gritty, sterile, free-draining rooting medium such as a mix of sand and perlite. Provide bottom heat (around 18-24°C or 65-75°F) and high humidity around the cuttings, either by placing them in a propagation chamber or covering them with a plastic bag. Keep in bright shade or filtered light. Rooting typically occurs reliably within 8-16 weeks. Once rooted, gradually acclimatize plants to ambient conditions before potting up.
General Cultivation
Heart Leaf Kōhūhū is a threatened shrub to small tree that prefers mild, frost-free microclimates and benefits from targeted site protection. Provide humus-rich, free-draining loams in bright shade to light woodland sun, sheltered from hot, desiccating winds. Maintain steady moisture through dry spells but avoid soggy roots; raised beds or bermed planting holes help on heavier soils. Juveniles benefit from a light, open canopy and weed-free root run; once established they tolerate moderate frost if well mulched. Avoid high-nitrogen fertilizers which push soft growth attractive to sap-suckers. Plant eco-sourced stock from the same catchment where possible. Staggered groupings under taller nurse species create the filtered light and shelter this pittosporum prefers.
Pests & Diseases
Poor drainage predisposes plants to root and collar rots; plant high and keep mulch clear of stems. In still, shaded corners, scale and sooty mould can build-improve airflow and wash foliage if needed. Browsing by possums and deer is locally significant; protect young plants until established.
Cultural Significance
Traditional Uses and Values
Lowland riparian forests hold cultural importance as mahinga kai and travel corridors; the rare trees and shrubs that persist in these remnants are valued as taonga species. Protecting P. obcordatum within living landscapes acknowledges whakapapa and supports the interwoven ecological and cultural heritage of Aotearoa’s river plains.
Bonus Tip
Cool, sheltered understorey conditions with even moisture suit this species; if you can keep a leaf‑litter mulch moist but the root collar dry, you are close to its natural niche.
