Mānuka

Mānuka (; ''Leptospermum scoparium'') is a species of flowering plant in the myrtle family Myrtaceae, native to New Zealand (including the Chatham Islands) and south-east Australia. Bees produce mānuka honey from its nectar.

The Latin specific epithet ''scoparium'' means 'like broom', referring to Northern Hemisphere genera such as ''Genista'' and ''Cytisus'' which it superficially resembles, but to which it is only distantly related.

Description

Mānuka is a prolific shrub-type tree and is often one of the first species to regenerate on cleared land. It is typically a shrub growing to tall, but can grow into a moderately sized tree, up to or so in height. It is evergreen, with dense branching and small leaves long and broad, with a short spine tip. The flowers are white, occasionally pink, – rarely up to – in diameter, with five petals. The wood is tough and hard.

Mānuka is often confused with the related species kānuka (''Kunzea ericoides'') – the easiest way to tell the difference between the two species in the field is to feel their foliage – mānuka leaves are prickly, while kānuka leaves are soft. Alternatively, the seed capsules of mānuka are large ( in diameter) and often remain on the plant year round, whereas the seed capsules of kānuka are much smaller ( in diameter) and are not present for much of the year.

History and habitat

Evidence suggests that ''Leptospermum scoparium'' originated in Australia before the onset of the Miocene aridity, and moved as a result of long-distance dispersal events to New Zealand from eastern Australia sometime during the last 20 million years. Cyclones and other wind activity are most likely responsible for transporting seeds long distances. Supporters of this claim cite evidence that the genus ''Leptospermum'' arose under conditions where frequent forest fires were common (i.e. in Australia, and not temperate New Zealand), because they possess fire-adaptive traits like serotiny and storage lignotubers. It has been postulated that on arrival in New Zealand, ''L. scoparium'' became established in limited edaphically suitable areas until the arrival of the Polynesian people, whose fire and forest-clearing brought about the low-nutrient-status soils for which it was preadapted in its homeland. It is now more common in New Zealand than it is in Australia. It is found throughout New Zealand, but is particularly common on the drier east coasts of the North and South Islands, and in Australia in Tasmania, Victoria and New South Wales.

Ecology

Fire ecology

Mānuka is one of the few New Zealand native species which are adapted to fire, able to respond to fire by opening seed pods and dispursing in recently disturbed ground.

Native bush regeneration

Mānuka can quickly colonise areas of disturbed land, and can create environments where other native species can establish more successfully. Because of this, mānuka is often utilised by conservation projects in New Zealand.

Pests and diseases

The adult mānuka beetle ('' Pyronota festiva'') and its larvae feed on ''Leptospermum scoparium'' in New Zealand. The scale insect, '' Eriococcus orariensis'', is a sap-sucking insect that feeds on ''L. scoparium''.

Pollinators

Pollinators that visit ''Leptospermum scoparium'' include ''Melangyna novaezelandiae'', ''Hylaeus'', and honeybees.

Continued evolution

''Leptospermum scoparium'' is in the process of evolutionary differentiation as a result of its isolation from fellow members of the ''Leptospermum'' genus. New studies demonstrate a loss of lignotubers among populations of ''Leptospermum scoparium'' located in relatively fire-free zones of New Zealand's South Island, while Australian and Tasmanian populations retain their lignotubers along with stronger manifestations of serotiny. Australian populations of ''Leptospermum scoparium'' are shown to be chemically distinct from their New Zealand counterparts, with significantly higher levels of cinteole and monoterpines. Chemotypical variations also exist between different populations within New Zealand, leading some to suggest that ''L. scoparium'' be divided into three subspecies: those with high pinenes, high triketones, and high sesquiterpenes. Recently, however, new research suggests that plant-to-plant variation far outstrips the variation seen between geographically isolated manuka sites, at least with regard to nectar chemistry.

Names

The name ''mānuka'' is Māori; it comes from Proto-Polynesian *''nukanuka'' or *''nuka'' which refers to ''Decaspermum fruticosum'' due to its similar small white flowers; it is a doublet