February - Hīnau - Native Plant of the Month
Hīnau were once known as New Zealand olives and their scientific name Eleocarpus means ‘olive-fruited’. While they are not actually related to the olives that you might enjoy on a pizza, the fruit of these trees do look very similar and were historically a prized Māori food. Somehow these previously celebrated trees have quietly slipped away from Auckland and they are now uncommon on the North Shore. We want to sing the praises of hīnau and bring this wonderful tree back to our local forests and back gardens.
Hīnau are endemic to Aotearoa and can be found throughout the North Island and in the South Island down to Christchurch, growing in coastal and lowland forests. They are one of only two native species in their genus in New Zealand, the other being pōkākā. The plants in this genus are usually identifiable from their clusters of white, bell-shaped flowers with lacy, frilled petal edges. Not many of our large native forest trees have showy flowers and hīnau can be quite show-stopping in a heavy flowering year. Trees flower from late spring into summer, with fruit ripening through autumn and winter.
Like many of our native plants, hīnau are heteroblastic. This means that juvenile plants have a different appearance to mature trees. Seedlings and saplings look extremely similar to young rewarewa. They have long, thin, flat leaves with distinct teeth along the margins and usually grow as a single, straight shoot. In the past hīnau saplings were sometimes tied in a knot and left to grow and harden for a few years. They were then cut and used as walking sticks with knotted handles. When not used as walking sticks, mature trees grow to around 20m tall, with a rounded crown. Trees grown in the open will usually not grow as tall. Adult leaves are leathery and shorter than juvenile leaves, with edges that roll under creating a curved surface. On leaf undersides, where veins meet the midrib, there are visible pits called domatia. Hīnau have fissured bark that was used to make baskets and containers and can be used to produce a black dye and ink. Large trees often develop hollows, which meant that their timber was not eagerly sought after. This tendency makes hīnau fabulous trees for providing habitat to our native wildlife however, particularly our native pekapeka/bats and parrots (like kakariki and kākā), who all rely on tree hollows for safe roosting and nesting sites.
While there are many features that make hīnau an attractive and important tree, it is their fruit that has gained them the most love. Hīnau fruit are small (just over 1cm long), oval and ripen from green to purplish black. Just like the olives that they were named after, the flesh of the fruit is oily with a high fatty acid content. It has a lightly perfumed smell when broken open. The fruit layer surrounds a hard grooved pit that contains a single seed. Hīnau fruit were made into carefully prepared and highly regarded food by Māori and trees were often deliberately planted near settlements for easy harvesting. The main item made from hīnau fruit was a kind of fermented cake made by separating the flesh of the fruit from the stones, pounding it into a mealy texture then compressing this into a mass that was steamed in a hangi and stored immersed in water for many months. A gruel made from hīnau fruit was eaten as a sick-bed food. As well as being sought out by people for their fruit, hīnau trees are important sources of food for our native birds. Kākā are especially of hīnau fruit, which they feed to their chicks. Kereru eat hīnau fruit and can distribute seeds over long distances. Kokako, weka and even kiwi eat hīnau fruit, with the flightless birds snaffling up fallen fruit from the forest floor.
Pests are never very late to the party and unsurprisingly possums, rats and mice are very fond of hīnau. Possums will browse leaves, flowers and fruit, preventing trees from being able to produce any seeds. They also enjoy using the hollows in hīnau trunks to hide out during the day, preventing our native species from using this shelter. A study has shown that possum health and breeding success are connected to hīnau fruit abundance. The high nutritional content of the fruit is also likely to benefit our native birds if the possums don’t beat them to it. Rats and mice seek out hīnau fruit and their strong teeth mean that they can chew their way into the hard seed cases and destroy the seed inside. All of these animals reduce the likelihood of hīnau trees to produce and disperse seeds. As you would expect, pest control is very beneficial for hīnau.
We do not know exactly why, but hīnau are now uncommon on the North Shore. There are a few individual trees known around Kaipātiki (including one that is protected as a notable tree) and a venerable, but damaged, specimen that is growing in the remnant forest around lake Pupuke at Sylvan Park. With all the benefits that these trees can provide to our native animals - particularly kākā, we would love to see more hīnau being planted, and greater care being taken of those that are surviving. If you know of a hīnau growing near you, let us know so that we can get a better idea of where specimens are located and we can try and support nursery growers to supply these wonderful trees. If you do manage to find a hīnau for sale, make sure to plant it somewhere with deep, rich soil, ideally in partial shade.