A distant cousin called Myrtle

Ann Graeme traces the links between the aromatic feijoa from South America and our beloved pöhutukawa and rätä trees.

Possums' pick

Pöhutukawa and northern and southern tree rätä are perhaps the best-known and best-loved of our native trees.

Sadly they are loved by possums too.

Possums strip the trees of their new, young leaves. Each leaf only lives for two
years so if the new growth is constantly browsed the tree will die.

Such was the fate of the pöhutukawa that clothed Rangitoto Island until a massive pest control operation in
1990 eliminated the possums (and the wallabies).

Tree rätä have been less fortunate. Few survive in the northern forests and their glory is only seen in forests like Wellington’s Kaitoke Regional Park where they have enjoyed decades of protection from possums.

In southern forests, the flowering South Island rätä trees run red along the Arthur’s Pass highway where possum control prevails, a sad contrast to the derelict trees in neighbouring possum ridden valleys.

When the feijoas fall in autumn so too do the seeds from the pöhutukawa. They swirl like dust into the yard, their tiny sharp seeds burrowing into abandoned
socks.

How strange, I think as I shake them out (for they are very itchy), that these two fruits are related. They had a common ancestor millions of years ago when New Zealand was part of the supercontinent Gondwana.

Feijoa, guava, pöhutukawa and rätä all belong to the myrtle family. Their fruits don’t look a bit alike, but their flowers give the game away. It’s not the petals that make the show, it’s the stamens. Brightly coloured and tipped with orange pollen, they are crowded like a pincushion around the central female stigma.

The feijoa is native to the lush forests of South America.

It likes a sheltered place and soil rich in nutrients to grow its fat, juicy fruit. They are designed to attract birds, bats and primates, which disperse the seeds in their droppings.

Pöhutukawa is much more rugged. It clings to rocky, windswept crags and forces its stems between boulders.

Its seeds are not wrapped in juicy fruit but have papery wings to carry them far and wide. The tiny seeds have little reserves of food and can’t cope with competition, but they can germinate in the most inhospitable cracks and crannies.

I have seen a cohort of hardy (or foolhardy) pöhutukawa seedlings growing on White Island, in a moonscape made barren by continuous volcanic eruptions. The seeds could
have blown all the way from Whale Island or the mainland.

Rätä trees, pöhutukawa’s cousins, have a similar strategy.

Few northern rätä trees start life on the forest floor. It’s too dark and crowded there. But high up in the trees among the perching plants are crevices where a tiny seed can lodge and grow. For years the rätä seedling will endure this uncertain life until its roots snake down to the ground and thicken and encircle the host tree.

Does it strangle its host? Opinions vary. Its host tree is already mature and the two grow together for many years.

Maybe the rätä hastens its host’s demise – but maybe it props it up in its old age.

Besides the tree rätä, there are several white-flowered climbing rätä and the magnificent scarlet rätä vine.

Rätä and pöhutukawa belong to the genus Metrosideros, which means heart of iron, a tribute to their very hard wood.

Iron-hearted too are their relations, the eucalypts, that huge assemblage of more than 700 species whose members have adapted to the extreme habitats of Australia.

Eucalyptus species range from some of the tallest trees on Earth – the karri of Western Australia and the misnamed mountain ash of South Australia – to the stubby multi-trunked mallee of the arid outback.

Eucalypts used to grow in New Zealand until they became extinct in cooler eras.

Like the eucalypts, mänuka and känuka are aromatic.

This is a distinguishing feature of the myrtle family. Tropical myrtles provide us with cloves and allspice, so prized that nations fought the legendary Spice Wars over the tiny Spice Islands where they originally grew.

The common myrtle was a valued plant in ancient Greece and Rome. It was used as perfume and in medicine and was the symbol of love and immortality.

In 1770 Carl Linnaeus, the father of plant taxonomy, used it to define the myrtle family. He based his classification on the number of parts in its flower, the single style – the female part – surrounded by many stamens – the male parts.

It seems ironic that he used the common myrtle, the only member of its family found growing around the Mediterranean, not knowing that the vast majority of myrtles would be discovered in the Southern Hemisphere, in South America, Australia and the Pacific region.

The common myrtle traces its ancestry through Africa to Gondwana.

But back to feijoas with their large, juicy fruit. They are quite unlike the woody fruits of mänuka and pöhutukawa, which dry and split and shake out seeds. We have only a few fleshy-fruited myrtles in New Zealand.

One is the popular shrub, ramarama, with its shiny, dimpled leaves.

Another is maire tawaka, or swamp maire, a wetland tree now quite uncommon because it has been destroyed by drainage and grazing. It’s an uncomfortable tree to walk around because it grows spiky aerial roots that stick up out of the sodden ground, absorbing oxygen for the roots to breathe. With its cream flowers and red fruits, it looks like its Australian relation, the acmena or lilly pilly.

So when the pöhutukawa and rätä flowers blaze, the mänuka blossom whitens the hillsides and later the feijoas fall, remember these plants are all connected, far back, in
the lost continent of Gondwana.