Overview
The Heart-leaved Kohuhu (Pittosporum obcordatum) is an exceptionally rare, divaricating shrub or small tree endemic to New Zealand. Discovered in 1840 near Kaitaia by botanist Ernst Dieffenbach, the species was subsequently feared extinct for over half a century before tiny remnant colonies were rediscovered in isolated swamp forests. Exhibiting the classic New Zealand divaricating architecture—a tangled thicket of interlaced, wiry branches bearing minute, heart-shaped leaves—it represents an evolutionary marvel finely tuned to riparian riverbeds and prehistoric browsing pressure.
Biology and Physical Characteristics
Pittosporum obcordatum grows as an upright, columnar shrub or small multi-trunked tree with slender, zig-zagging, wiry grey-black branches that interlock at wide angles to form a dense outer cage. Its juvenile and adult foliage consists of tiny, distinctly obcordate (inversely heart-shaped) leaves with a notched apex, measuring barely a few millimeters across. In late spring and early summer, the plant produces an abundance of sweetly scented, diminutive flowers ranging in color from pale cream and yellow to deep purplish-red, which emit an intoxicating vanilla-clove fragrance at dusk to attract nocturnal moths.
Behavior and Ecology
The tangled divaricating habit of Pittosporum obcordatum is widely recognized as an ancient evolutionary defense against browsing by extinct giant flightless moa. The tough, springy outer twigs shield interior foliage and blossoms from being stripped. Ecologically, it is restricted to periodically inundated lowland alluvial river terraces, where deep silt deposits and seasonal winter waterlogging prevent taller forest trees from establishing dense canopy cover, allowing the shrub to capture filtered understory sunlight.
Conservation and Human Impact
Once widespread across New Zealand’s lowland river plains, Pittosporum obcordatum has lost over 95 percent of its primeval habitat due to catastrophic wetland drainage and clearance for pastoral agriculture. Surviving populations are small, severely fragmented, and often consist of aging adult trees unable to regenerate naturally due to livestock grazing and invasive pasture grasses. Conservation efforts led by the QEII National Trust and Department of Conservation involve fencing off privately owned forest remnants, undertaking intensive weed control, and planting eco-sourced nursery seedlings.
Interesting Factoid
After being first collected in 1840, this elusive ‘heart-leaved’ tree vanished so completely from European records that botanists searched in vain for nearly 60 years before a solitary surviving grove was stumbled upon in 1901!
Last updated: October 2026