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Leptospermum (and Kunzea) through the Ages
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This article was published in The Fringe, December 2016

Manuka and Kanuka.

When Captain Cook, Joseph Banks and Daniel Carl Solander arrived in Poverty Bay on 7th October, 1769 they found a new world of plants and birds unlike any they had seen before.

It was springtime when they encountered the first inhabitants, a meeting that did not go well, resulting in the deaths of several Maori. Despite the unfortunate incident they were able to go ashore and collect the herbs Cook wanted to feed to his crew to prevent scurvy. Prominent among the plants were two very similar looking species, one flowering, the other not, that they no doubt recognised as belonging to the Myrtaceae family, but they were then unknown and unnamed.

Dr Daniel Carl Solander was a Swede who had studied under Linnaeus, the world's pre-eminent botanist, before taking a position at the British Museum. When invited by Banks to join the expedition to the Southern Hemisphere to observe the transit of Venus, he accepted subject to having 3 artists (all of whom died on the voyage) to record the places and plants as they were discovered.

In one of the historic twists of fate that early explorers encountered, the hundreds of plants and the accompanying sketches and paintings collected by Banks and Solander, were taken safely to England, where they were redrawn, described and named in a manuscript entitled "Primitiae Florae Novae Zelandiae". There they languished unpublished due to a wrangle between Banks, the Admiralty and the Treasury. Had the manuscript been published as intended we would be using the names Banks and Solander conferred on the more than 350 new species they collected. Later botanists, such as the Forsters (father and son) on Cook's second voyage, had their own frustrations with British authorities, but they got the honour of publishing names for the plants they collected including the names of Leptospermum scoparium (manuka) and Leptospermum ericoides (kanuka).

Manuka and kanuka have generally been treated as one species, with most people not recognising the differences, or the importance of knowing which habitat each species prefers. Manuka is generally on wetter or impoverished soils while kanuka thrives on drier hillsides.

They can be identified in several ways.

Manuka is predominantly spring flowering although it has a secondary flowering in late  summer. Its white flowers, some with a tinge of pink, are 1 - 2.5cm in diameter and they develop into hard, durable seed capsules more than half a centimetre in diameter. Its leaves, normally quite sharp pointed, are between 0.5 and 2 cm long and 0.5cm or more wide. The grey/red/brown bark is normally 'tatty' and peels off in short scruffy pieces, and the wood when cut can be distinctly red giving the early European name of "red tea tree". Manuka can grow to 5 or 6 metres tall, is seldom more than 10cm in diameter and lives 40 or 50 years, although exceptionally they can develop a trunk half a metre thick and live to 100 years.

Kanuka is different in almost all aspects but until you learn the differences they can be hard to determine. Kanuka brings a white Christmas to New Zealand by flowering at Xmas time.

Kanuka also has white flowers, but they are considerably smaller than manuka flowers, never much more than 1 cm in diameter, and their capsules are also smaller, less than half a centimetre in diameter. Kanuka has soft, not sharp leaves, that tend to be narrower relative to their length than manuka leaves, seldom being more than 3mm wide to a length that may vary from 1 - 3 cm. Kanuka bark is more of a silvery grey colour and tends to peel off the tree in long slender strips. The colonial name "white tea tree" refers to the colour of the wood, not the flower.

With so many differences it was decided in 1983 that kanuka better fits the Australian genus of Kunzea than Leptospermum to which the Forsters attributed it. The species name of ericoides was retained and other than a low growing form on Great Barrier Island, all the kanuka throughout the country was known as Kunzea ericoides. Then in 2014 Auckland DoC botanist Peter de Lange redefined New Zealand Kunzea, identifying a total of 10 species including Kunzea ericoides which is confined to where the Forsters saw and described it in Northwest Nelson. The Waitakere form has been named Kunzea robusta and is the largest growing form reaching a height of up to 30 metres and a trunk diameter of one metre. They can live for around 150 years.

Generally the best identifying characteristic is the capsule. Manuka flowers while very young, and the developed capsules can remain prominently on the branches for many years before opening to release their seed, whereas kanuka's smaller capsules generally open in the autumn following flowering, and frequently drop off the branch within a few months, so by spring it can be difficult to find a capsule on some trees.

Just to complicate the story early botanists recognised that Leptospermum scoparium includes "a myriad of varieties" and "multitudinous forms imperfectly known". With modern DNA techniques it is now possible to determine more accurately whether or not there should be several new species of manuka created out of the existing Leptospermum scoparium.

Of course nature has known that there is huge variability among the composite forms we call manuka, to the extent that some animal and insect species have evolved to live their lives on just one form of manuka, and never adjust to moving onto a differing form which may grow adjacent to their preferred host tree. Such speciation may be for a number of reasons, but as the world has been modified by the influence of modern man, those specialist creatures are at great risk of being driven to extinction.

One rapidly developing situation could see the increasing numbers of introduced honeybees lead to the decline of many endemic native species. Man's determination to maximise profits by overloading an environment with increasing numbers of hives can only be to the detriment of the native biota. Precious resources essential for native species such as insects and bats which rely on a limited range of plants, will be depleted by the thousands upon thousands of foraging bees, efficiently collecting pollen and nectar in vast quantities. Having been part of a balanced ecosystem for millions of years, these native species could be exterminated without our knowing it in a matter of years. Many of these insects have not been discovered yet, let alone identified and named.

Many bee-keepers are planting extensive areas of manuka to provide still more habitat for bees, yet we don't even know the differences among the "multitudinous forms" to even attempt to match the habitat with the form. All the apiarist wants is maximum production and chooses his manuka plants on the assumption that a known form produces more of the active ingredient that his customers are wanting. It may be good business but it is not good for the environment. Much more research is needed, particularly before permission is granted to beekeepers seeking to place hives in currently protected native bush blocks such as the large DoC estates.



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