The much-maligned, multi-purpose mānuka

Whether it is called mānuka, tea tree or kahikātoa – as it’s known to some iwi – mānuka is a plant that causes some controversy, as Natalie Spyksma outlines.

Where some people see mānuka (Leptospermum scoparium) simply as invasive scrub, others see it as an essential coloniser. Some see its commercial properties, be it honey, firewood, floristry or medicine, whereas others think of it merely as a pretty garden shrub.

As a guide on Tiritiri Matangi, mānuka honey is the most common association I hear mentioned. The second is “the black stuff” that grows on mānuka, but more about that later. Without a doubt though, it is one of our most floriferous and recognisable native plants, so let’s delve a little bit deeper into its story.

Some background

Mānuka occupies a place in Aotearoa/ New Zealand’s ecosystem as a successional species. However, good sunlight is a prerequisite for the plant’s survival. Within 30-50 years, it is replaced by plants once nurtured in its undergrowth.

Its hardiness and indifference to soil types has given rise to a variety of forms, ranging from prostrate ground covers in the volcanic regions, to elegant trees

One of our most floriferous – or flowerbearing – native plants. The typically wild white or a white-flushed pink mānuka (left) is now available in a red cultivar (above, top). Once the seed pod opens (above), the wind can readily spread the seeds. Opposite page: Each flower has a distinctive circle of male stamens, surrounding the central female carpel.

5-10m tall, to stunted, wind-blown shrubs on exposed sites. Competition is fierce.

As Aotearoa’s main pioneer shrub, it loves nothing more than colonising bare slopes, forest margins, pastures and open land, where often barely a thought is given to its magnificent displays of flowers.

However, no matter their shape, all possess small, aromatic and prickly leaves, singular white-flushed flowers with a distinctive circle of stamens and hard, woody seed capsules. When dry or burnt, these open to release thousands of fine, light seeds to the ground or for dispersal by the wind.

How mānuka got its name

To Māori, mānuka’s striking white flowers held a resemblance to the Polynesian nukānuka tree, Decaspermum fruticosum. Simply the prefix mā was added to the word root, nuka, to name this new plant.

Captain Cook brewed tea from the leaves, giving rise to the common name, tea tree.

Botanically, the Greek leptos (slender) and sperma (seed) reference slender seeds. Scoparium (broom-like) references twiggy branches which, in earlier days, served as brooms. Mānuka is a member of the Myrtaceae family.

The origins of the mānuka

Thousands of years ago, mānuka is thought to have self-introduced on the wind from Australia, where fire is a constant in Leptospermum’s life cycle. Seed pods that open with fire, and past evidence of lignotubers – a woody swelling at the root crown that protects against fire – are testament to this.

Mānuka is often mistaken for its lookalike, the endemic kānuka (Kunzea ericoides) but, in contrast, kānuka’s foliage is soft, often droopy and the white flowers are much smaller. Kānuka grows up to 20m tall.

On Tiritiri Matangi, there is a saying, “Mānuka is mean (prickly), kānuka is kind (soft)”. This helps to differentiate the two by touch. I always feel a bit sorry for mānuka with this description.

Human influence

When Māori first arrived, a damp, largely forested Aotearoa presented only small opportunities for mānuka to grow. It is thought that the clearing of bush by hand and fire, mainly for thoroughfare, allowed mānuka to spread.

Regular reburning to keep the thoroughfares open meant it could continually re-establish itself, eventually thriving from sea level to 1800m. Conflict, perhaps unrecognised as such, had begun between mānuka and humans.

With the arrival of Europeans, when land was cleared for animal farming, mānuka, of course, was quick to reestablish itself in pasture wherever it could. Stock didn’t find it palatable and, as mānuka can flower and reseed when only a few centimetres tall, a new battle began. Machinery, then herbicides, became the tools for compliance.

Multi-purpose mānuka

Aside from the shroud of unwitting conflict, mānuka’s uses were valued and many. Māori crafted all manner of things, including paddles, weapons, spades and bird spears, from the hard, red wood – and the bark was used for water containers and as a waterproofing agent.

Medicinal properties were recognised and resulting decoctions were used as mouth washes, antiseptics, medicine and wound dressings.

Settlers used the wood to build shelters and fences, and the slow, hot-burning wood for cooking and heating. Even today, mānuka firewood is considered the best. However, the clearing of land for this purpose is now discouraged.

Popularity spreads to gardens and floristry – but also attracts bugs

Plant breeders and nurserymen certainly noticed the virtues of mānuka’s floriferous ways, and now the home gardener and floristry industry have an array of white, pink or red varieties from which to choose. Flowering times vary throughout the country, ranging from autumn through winter to spring.

Unfortunately, sooty mould – the black fungus that grows on the plants as a result of the sticky secretions (honeydew) from scale insects – can be a troublesome pest on mānuka. The mould itself doesn’t feed on the plant but, as it covers the leaf surface, it blocks light and reduces photosynthesis, essential for plant life. If the insect is removed, the sooty mould eventually dries up or washes off. Organic Neem Oil is useful for this.

Mānuka becomes a medicine

Prior to the introduction of honeybees in 1839, solitary native bees, hover flies, moths, beetles and geckos were the main pollinators of mānuka’s sweet-smelling flowers. The balance has no doubt changed as apiculture has grown.

Interestingly, honeybees are now the world’s most widely farmed insect and entomologists are raising concerns.

Since the 1990s, research has catapulted mānuka honey’s unique antibacterial, antioxidant, antimicrobial and antiinflammatory properties on to the world stage. A huge increase in honey production and consumption has followed, along with the development of a burgeoning medicinal, health and wellbeing industry worth billions of dollars.

Controversy recently erupted between Australia and New Zealand’s honey industries over Australia’s desire to trademark the words “mānuka honey” to market honey from their own native Leptospermum scoparium trees. Early in 2023, the UK High Court ruled in Australia’s favour.

The tables have turned and now many hectares of mānuka are being planted throughout Aotearoa, not only for honey production but also for restoration projects. A new chapter of respect and association has emerged.

Naturally, mānuka was widely used in Tiritiri Matangi’s replanting programme and is easily viewed along existing tracks and road margins.