February in the hills with Barbara Mitcalfe and Chris Horne
Elaeocarpus dentatus, hīnau
Elaeocarpus means seeds like olives and dentatus means toothed, referring to the flower petals of this endemic NZ tree. A lowland forest species, hīnau grows throughout the North Island. In the South Island, it reaches to Christchurch in the east and south Westland in the west. Its rounded crown is often seen in the canopy of tall broadleaf forest. Sometimes emergent, hīnau can grow to 20 m high, with a diameter of 1 m. The contribution made by such a long-lived tree, to the ecosystem of which it is a significant part, must be immense. A whole community of insects, birds and epiphytic plants, finds homes in its crown. In season, birds flock to eat juicy hīnau fruit, and it is likely that bees also visit its scented flowers.
Hīnau's adult leaves are usually alternate and are up to 12 cm x 3 cm. Occasionally finely serrated, they are broader towards the pointed tip, and their edges typically curl under. They tend to be arranged in erect clusters at the end of the twigs, making hīnau identification relatively simple, even from a distance. They have a firm texture and are dark green. (Compare the juvenile hīnau leaves, described below). If you turn over an adult hīnau leaf, you may see a few tiny triangular 'pocket' domatia on the underside, where the veins meet the midrib. The function of domatia is not known for sure, but they are usually inhabited by minute insects, so perhaps they have a symbiotic relationship.
Juvenile hīnau leaves are quite different. A tiny hīnau seedling (e.g. less than 15 cm high), has leaves shaped like the adult's, but they're flimsy, more serrated, and sometimes have brownish freckle-like splodges. By the time the seedling has grown to c. 1m high, it has developed long, narrow, parallel-sided leaves (up to 20 cm x 3 cm) that poke straight out from the main stem at right angles. They are often mistaken for juvenile rewarewa, but rewarewa leaves are paler green with much coarser serrations.
Hīnau flowers are bisexual, white, with ragged-edged petals, and lightly sweet-scented. They hang like lily-of-the-valley flowers, in racemes along the stem.
Hīnau fruit are c. 2 cm x 1cm, fleshy, pendulous, purple-brown, with kernels like olives. Māori used to stone-grind the kernels finely, producing a granular meal known to be highly nutritious. They then bound the mixture with water and cooked it in flat cakes, either in an umu or on hot stones. The result of this laborious process was considered a great delicacy, reserved for invalids or special guests.
Hīnau bark is greyish, with shallow vertical furrows. Occasionally hīnau trunks become hollow, yet characteristically, the trees continue to grow and thrive, producing enough sound, food-and water-conducting tissue around the hollow core to last for scores of years. Next time you're in Wellington Botanic Garden you may note two hollow hīnau still flowering and fruiting. One of them is beside the track, near the top of Hīnau Path, and the other is on the true right of Stable Gully.
The high tannin content of the bark was well known and used by Māori to dye black the scraped portions of flax garments, producing contrasting patterns. A solution of hīnau bark, which is highly astringent, was also used externally to treat some skin complaints. This was its main rongoa use.