Kahikātoa / Mānuka in general
Peat bog mānuka, Leptospermum repo
Tairāwhiti mānuka, Leptospermum tairawhitiense
North Island kahikātoa, Leptospermum hoipolloi
Kahikātoa in poetry and whakatauākī
Mānuka Blight
Myrtle Rust
Introduction: Kahikātoa / Mānuka in general
 On this page we are using the words Mānuka and Kahikātoa interchangeably to refer to New Zealand members of the genus Leptospermum. Mānuka is now the more general term used throughout the country, and Kahikātoa the term formerly most commonly used in the Taitokerau region (although also used elsewhere) for plants now classified botanically as either Leptospermum hoipolloi or L. scoparium s.s. The latter name now refers to the varieties of Mānuka with broader oval, roundish or oblong leaves, all tapering to the typical pointed tip (see the papers by Luzie Schmid (2023), Peter de Lange (2021, 2023) and associates in the bibliography for more information about the reasons for this realignment of New Zealand species of Leptospermum). The composite picture on the left illustrates the foliage and flowers typical of Leptospermum scoparium s.s. It should be noted that while the division of Leptospermum scoparium s.l. outlined on this page is accepted by many botanists internationally, not all New Zealand or overseas botanists are currently in agreement; among other things, the revised classification has political and economic as well as scientific ramifications. [The abbreviation s.s. stands for sensu stricto, "in the strict sense" i.e. "strictly speaking", and s.l. for sensu lato, "in a broad sense".]
The Mānuka/Kahikātoa grouped together by botanists in the genus Leptospermum and until recently sharing the specific name L. scoparium are a very important set of small trees by any name. Trees of one species, L. hoipolloi, occasionally grow up to about 10 metres high, but around 4 m. would be the normal height, with fully-grown plants of L. repo often much shorter. Kahikātoa trees are found in a wide variety of soils in open places. They act as a nurse tree for regenerating forests. The flowers are very attractive, much larger than those of the kānuka with which in some districts they share a name (over a centimetre wide, compared with a few milimetres). The Kānuka and Kahikaatoa are very similar trees in many ways but the kānuka has soft (rather than prickly) leaves, and several species grow three or four times higher than the tallest kahikātoa. Also, Mānuka (Kahikaatoa) leaves, which have aromatic glands on the undersides, and leaf-tips are aromatic when crushed, whereas the leaf tips of the Kānuka (despite its also being called "tea tree" in English), are much less so.
The excellence of these trees for heavy-duty work that required a slender, durable, sharp object is captured in this proverb, comparing the comparatively tiny kahikātoa to the mighty tōtara, one of the kings of the forest:
He iti kahikātoa pakaru rikiriki te tōtara
The little kahikaatoa can reduce the mighty tōtara to tiny splinters. [M & G #419]
The wood is very strong and hard, excellent for weapons and agricultural implements. As the proverb notes, as well as for the weapons that could defeat mighty warriors, the kahikaatoa was the ideal timber for wedges used for the felling and dismemberment of large trees, and thus a symbol of what could be achieved by anyone with the requisite determination and resilience.
The red wood also makes excellent firewood, which, along with the fashion for clearing land for dairy farms, has depleted stocks of the timber in many places where it was once abundant. However it is a resilient tree in adverse conditions, and can quickly re-colonize abandoned land and act as a nurse tree for regenerating native forest.
Traditionally the thin branches of both kānuka and kahikātoa were used extensively for making stout fences and other structures from the intertwined twigs woven together. The name for this process, rauwiri (and variants rauiri and rawiri) came to be used for both the fences and the trees themselves. The genus Leptospermum originated on the Australian mainland. The ancestors of all the New Zealand species arrived in New Zealand from Tasmania, probably within the last million years, and further differentiation took place here. Recent genetic studies (e.g. Buys et al. 2019 and Koot et al. 2022) have confirmed the existence of distinct strains within the New Zealand species, and the genetic separation of all New Zealand species from their Tasmanian counterparts. The study by Matt Buys and associates explicitly concluded that there was sufficient evidence to make Leptospermum scoparium (i.e. the species name as representative of the New Zealand plants hitherto covered by that name) endemic to New Zealand.
 Bees are attracted to the nectar-laden flowers, and mānuka honey produced from kahikātoa/mānuka flowers (those of New Zealand varieties of Leptospermum scoparium sensu lato [broadly speaking])
is now a major industry; from being a cheap, everyday honey a few decades ago it now attracts premium prices in New Zealand and overseas, and its production is carefully regulated. The nectar contains a powerful antibacterial agent, methylglyoxal (MGO), which is
the result of the transformation of the saccharide dihydroxyacetone (DHA) into MGO. We know that mānuka flowers contain green nectaries (rather than white, as in most flowers), and that these enable the production of DHA through photosynthesis -- the more sunlight the mānuka flower receives, the higher the level of DHA in the nectar (see the 2021 paper by Professor Michael Clearwater and associates for more information about this). The resulting transformation of DHA into MGO occurs naturally with time and warmth [see note 1, References and further readings, below] without the assistance of enzymes. The "Unique Manuka Factor" in honey is now considered to be mainly proportional to the MGO content [see note 2] though factors contributing to the residual variation in activity and differences between regions are largely unknown. The qualities, attributes, and variations of mānuka honey are still the subject of intense research at the University of Waikato (where the UMF phenomenon was first detected) and elsewhere.
There is more informaton about this on the page for the name mānuka.
After the transfer of the species formerly known as Leptospermum ericoides s.l. (Kānuka) and L. sinclairii (Great Barrier Kānuka) to the genus Kunzea, the genus Leptospermum in Aotearoa was represented in the native flora by two named varieties of Leptospermum scoparium: L. scoparium var. scoparium,
based on a description by the Forsters in 1776 with reference to a specimen thought to have been collected from Dusky Sound (in the southwest corner of the South Island), which was assumed to be representative of similar trees found throughout the country, and L. scoparium (now L. hoipolloi) var. incanum (illustrated above, left), a generally smaller shrub or tree usually with pink flowers, although these may sometimes be dark red, and occasionally white. It is confined naturally to Northland from the Aupouri Peninsula to Ahipara, then east to Whangaroa, and is now (2024) classified as a form of a new species, Leptospermum hoipolloi (see below).
Leptospermum scoparium (in this case, from a still contested New Zealand point of view -- not all Australasian botanists accept the changes noted here) remains a catch-all name for other types of mānuka found occurring naturally throughout the South Island, which are characterized by their oval, rounded or oblong leaves tapering or ending with a sharp tip (rather than the narrower, lance-like leaves of the North Island species), along with North Island plants with similar characteristics. They have a monopoly of South Island habitats, except for the northwest corner. Some South Island strains of L. scoparium s.l. show similarities with Tasmanian plants, but differ in important respects, including the absence of lignotubers at the base which enable the Tasmanian plants to regenerate quickly after fire. The other strains of L. scoparium in New Zealand are also distinct from their Australian counterparts, and research has been under way which is progressively resulting in the complete taxonomic separation of the NZ plants from the Australian varieties currently sharing the same specific name.
Peat Bog Mānuka: Leptospermum repo
  The first stage of this revision process was completed when a plant community formerly subsumed under L. scoparium found in peat bogs and the fringes of peat lakes was formally identified as a new species, and appropriately named Leptospermum repo. It has been described in a paper by Dr Peter de Lange and an associate published in 2021 (see Bibliography for details). L. repo is a rather spindly, small shrub or tree, sometimes only a metre or so tall, occasionally reaching about 6 metres in favourable habitats. This species was once probably widely distributed in northern Aotearoa, but, as its natural habitats have been destroyed by changes in land use, is now confined to a small number of remnant bog ecosystems mainly in the Waikato.
This paragraph is flanked by images of the foliage (note the narrow, attenuated leaves) and the flowers (note the white stamens) of plants of this species of mānuka/kahikātoa, taken from the 2021 paper.
Like the other plants in the myrtle family, this plant is also endangered by the spread of the fungal disease myrtle rust (see below) a wind-borne fungal disease potentially fatal to infected trees.
Tairāwhiti Mānuka: Leptospermum tairawhitiense
 Mānuka growing in the East Cape area has been found to be genetically distinct from other New Zealand species. They also have unusually high levels of triketones in their leaves. Triketones are organic chemical compounds with strong anti-bactarial, anti-fungal and anti-inflammatory properties, some of the key medicinal elements present in mānuka oil. A paper by G.J. Atkins, Peter de Lange and M.A.M. Renner (2003) has formally established the East Coast plants as constituting a new species, Leptospermum tairawhitiense. They grow up to 4 m. tall, with very short leaves (3-9 mm long x 1-2 mm wide) densely crowded along the branchlets. The leaves have numerous oil glands and are spicy-scented when crushed. The tree has a short, dense branching habit, and unusually for New Zealand mānuka, will produce suckers from the base, which in suitable habitats (e.g. flood-prone river flats) will enable a single plant to develop into a colony. The white flowers are cupped (rather than flat when fully open, like those of L. hoipolloi) and smaller than other species -- 8-14 mm in diameter. They are produced sporadically through the year, but there is a short period of intense flowering in October and November. The short leaves make the male flowers conspicuous and appear larger than they really are.
This species is found naturally on river flats and places subject to frequent flooding along with adjacent coastal shrublands and reverting pasture from Hawai (aboout 25 km east of Ōpōtiki) to Uawa (at the southern tip of Tolaga Bay). The illustration above, taken from the Atkins et al. paper, shows (A) the inflorescence with both "perfect" (having both pistils and stamens) and male (lacking a pistil) flowers, (B) flowers showing the cupped shape, and (C) a mature, unopened seed capsule. All were taken by Peter de Lange, in different localities in the Tairāwhiti / East Cape region. At present this species is not threatened by myrtle rust, but its restricted natural range, economic importance and cultural significance to the Whānau-a-Apanui, Ngāi Tai, and Ngāti Porou tāngata whenua make it especially important that this remains the case.
North Island Kahikātoa: Leptospermum hoipolloi
 Analysis of the genetic and morphological data in the light of accumulated research findings and fieldwork has resulted in the publication of a paper by Luzie Schmid, Peter de Lange and Andrew Marshall which has placed most North Island mānuka in a new species, Leptospermum hoipolloi, formally established in their paper published in 2023. This species takes one of three major forms -- variants showng some morphological and genetic differences, often charactistic of plants in a particular geographical area, but blending in with each other so as to remain part of a single species. One of these, L. hoipolloi f. incanum has been described and illustrated in the introductory section, above. This is confined to the far north, from Pawarenga across to Mangonui and the Aupouri peninsula. A second northern variant, L. hoipolloi f. procumbens (illustrated on the left, in its natural habitat on the Kauere Coastal Track on the Aupouri Peninsula), is naturally confined to a narrow strip along the east coast from North Cape to about Leigh, including the offshore islands, and across to the eastern side of the Coromandel Peninsula as far south as Tairua. It is often found outside this range as it is a popular garden plant. This form is a prostrate plant forming patches up to 6m in diameter of often interlocking branches, which may develop roots when in contact with the soil. The young leaves are silver-grey to silvery white, becaue of a dense hair covering, and become red-green, green or dark green when mature. They are slightly concave in shape, and normally vary from about 11 x 2.2 to 14 x 2.8 mm in length and breadth. The flowers have 5 petals and are spreading when fully opened; they are usually white, but may occasionally be pink or tinged with pink. The plant likes to cover bare ground or rocky outcrops, where it may be found in association with kānuka (Kunzea spp.), several species of Coprosma, and rauaruhe (Pteridium esculentum), among other native species.
 Most members of this species however fall within the ambit of L. hoipolloi f. hoipolloi, the common everyday mānuka (as its name suggests) found throughout the North Island and in the Northwest tip of the South Island, from the Abel Tasman National Park down to Charleston (a little south of Westport), as well as a few areas in the Marlborough Sounds. It grows in a wide range of habitats from the coast to about 900 m above sea level, and thrives on regenerating areas and gumland. Once regarded as a weed, it has now been widely planted as the primary source of mānuka honey, as well as for native flora restoration and as a garden plant. This essentially is the kahikātoa of the proverbs and poetry, the manuka of mānuka honey, and the red mānuka of firewood merchants and popular imagination. The height of these trees depends very much on where they happen to be growing. In wet, poorly drained soils they may reach only a metre high -- or ten centimetres in extremely acid wetlands. In excellent conditions they can reach ten metres, although in most places mature trees will be 3 or 4 metres tall. The flowers have 5, sometmes 6 petals and are around 2 cm wide, flat when expanded and generally white, sometimes tinged pink, more rarely solid pink. The leaves (illustrated on the right on a plant from the Karikari peninsula) range from 10.6 to 17.8 mm and about 2.8 cm wide (sometimes proportionately a little longer or shorter), tapering to a pointed tip.
Kahikātoa in Poetry and Whakatauākī
The valued qualities of kahikātoa are reflected in many proverbs besides the one already quoted. It is sometimes also compared favourably with other trees:
Te paku peke tāne kaha, te iti kahikātoa.
[The strength of a small man is like a kahikātoa -- or,
The tanekaha (Phyllocladus trichomanoides) is pliable, but red mānuka is strong and durable. [M&G #2393]
He iti,
he iti kahikātoa
Although it is small, it is red mānuka. [M&G #417]
Nui pūwhāwhā, iti kahikātoa.
Big but hollow inside; tiny but red mānuka [M&G #1994]
That is, don't be taken in by appearances of affluence or grandeur!
The famous oriori (geneological lullaby) Pinepine te kura (Ngā Mōteatea # 215), welcoming the child into the world, identifies the kahikātoa as a source of strength, against the adversities which lie ahead: (NM 215, 7-9)
Nau mai e tama, ki te taiao nei
Kia whakangungua koe ki te kahikātoa
Ki te tūmatakuru, ki te taraongaonga.
[Welcome o Son, Welcome to this world of life,
You are to be ritually strengthened with the kahikātoa
With the tūmatakuru and the taraongaonga. N.M. vol 3, no. 215]
That is, he would be taught the weapons of war, symbolized by the kahikātoa, so that he could defend himself against formidable obstacles, symbolized by the tūmatakuru (spear grass) and taraongaonga (nettles).
Follow the links to the Proto-Polynesian names for more information (and speculation) about the etymology of Mānuka and Kahikaatoa.
Manuka Blight
 There are many named cultivated varieties of kāhikatoa, often derived from strains of Leptospermum hoipolloi f. incanum, but those we have tried growing all succumbed to "manuka blight" after a few years. The blight is the effect of infestation by the Australian scale insect Eriococcus orariensis, illustrated on the left, which weakens the plant by drawing out large quantities of sap, and providing an environment for the growth of a sooty fungus which covers the stems and leaves. The insect apparently arrived in Aotearoa by accident, but was propagated by farmers wishing to get rid of mānuka, once regarded as a weed, on their farms. There are many mānuka (mostly grown from the seed of wild plants) in the garden which have been used as nurse plants. These plants sourced from the wild have held their own, but seem to begin to die of old age after fifteen or twenty years. (They are naturally a short-lived tree, and as nurse plants will also die out once they are overshadowed by the trees they have fostered.)
Myrtle Rust
 An even more serious threat to mānuka, and all other members of the myrtle family like ramarama (see photo, left), pohutukawa and rātā is the fungal disease myrtle rust. This is caused by the fungus Austropuccinia psidii, the tiny spores of which are carried by the wind -- it reached Australia from South America (where it is endemic) in 2010, and had reached Aotearoa by 2017 when it was discovered in a Kerikeri nursery, after earlier being detected on Rauol Island (Kermadecs). It has now spread throughout New Zealand, despite attempts to eradicate it, affecting both native and exotic (e.g. Eucalyptus) trees. There is a succinct description of its effects in this extract from a Ministry of Primary Industries / Department of Conservation poster:
Myrtle rust attacks soft new growth including shoots, leaves, buds, flowers
and fruit. It can affect seed development. Repeated infections of this
fungal disease can kill the plant.
Symptoms to look out for on plants from the myrtle family are:
» Bright yellow powdery eruptions appearing on leaves and stems
» brown/grey rust pustules (older spores) on older infected areas
» Some leaves may become buckled or twisted and die off.
The following advice is given if you notice myrtle rust on any plants:
» Don't touch the plant or the infected area – this could spread the tiny spores which are fine like talcum powder.
» Take a photo – of both the powdery patches and the plant itself.
» Take careful note of the site so you can find it again. Mark it if possible with tape, ribbon, rope etc.
» Phone MPI's hotline 0800 80 99 66.
Myrtle rust can be spread from clothes and gardening equipment, so if you have been in contact with infected plants, wash your clothes on a hot wash, and also thoroughly wash any equipment before using it elsewhere. There is comprehensive information about this menace and how to deal with it on the interagency Myrtlerust website.
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