Karaka (tree)

Karaka
A mature tree in Glendowie, a suburb of Auckland, New Zealand.
Conservation status
Not Threatened (NZ TCS)[1]
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Cucurbitales
Family:	Corynocarpaceae
Genus:	Corynocarpus
Species:	C. laevigatus
Binomial name
Corynocarpus laevigatus J.R.Forst. & G.Forst., 1776

Karaka or New Zealand laurel (Corynocarpus laevigatus) is a medium-sized evergreen tree in the family Corynocarpaceae. It is endemic to New Zealand and is common throughout the North Island and less common in the South Island. Karaka are also found on the Chatham Islands, Kermadec Islands, and the Three Kings Islands. It is mostly a coastal tree, though in the North Island, it can also be found in lowland inland forests.

Karaka was first described by the German naturalists Johann Reinhold Forster and Georg Forster in 1776. Karaka grows to heights up to 15–20 m (49–66 ft) and has a stout trunk up to 60 cm (24 in) in diameter. Its leaves are leathery, dark to bright green in colour and up to 15–30 cm (6–12 in) long and its oval shaped orange-coloured fruit is 30–40 mm (1.2–1.6 in) in length. Karaka is a valuable food source for the kererū (Hemiphaga novaeseelandiae) and the Chatham Islands pigeon (Hemiphaga chathamensis). It is naturalised and considered an invasive species in several Hawaiian islands and is mostly found on the island of Kauai. Karaka is also grown in Southern California.

Karaka is considered a taonga (cultural treasure) amongst the Māori and Moriori peoples, who used it significantly as a food source. On the Chatham Islands, carvings of Moriori ancestors were carved on to karaka trees (known as rākau momori) are considered internationally significant and unique to their culture. An exoplanet originally named HD 137388 was renamed to "Karaka" in 2019 in recognition of the tree's orange-coloured fruit.

Karaka is a medium-sized evergreen leafy canopy tree with erect spreading branches. It grows to heights up to 15–20 m (49–66 ft) and has a stout trunk usually up to 60 cm (24 in) in diameter. The largest trunk's diameter ever measured was 3 m (10 ft).^[2][3] Karaka is predominantly a coastal tree, though in the North Island, it can also be found in lowland inland forests.^[4][5]

Mature trees have dark brown corrugated bark with corrugations that are broken up into pieces that are roughly 1 cm × 3 cm (0.4 in × 1.2 in) and 0.5 cm (0.2 in) thick. Younger trees have light brown bark that frequently has short, horizontal bands that resemble sewing stitches. Karaka's dense shade and prolific seeding exclude local species and change the host community's composition and ecological processes in areas where it has been allowed to proliferate. Karaka has an alternating elliptic oval shaped foliage that are up to 8 cm (3 in) wide, with petioles less than 2 cm (0.8 in) long.^[6]

From August to November, karaka produces large, stout, erect panicles of tiny greenish-yellow flowers, each less than 0.5 cm (0.2 in) in diameter. It starts flowering between August to November and each panicle may have up to 100–200 flowers.^[2][3] The fruit karaka produces is oval shaped and 30–40 mm (1.2–1.6 in) in length; with pale yellow–orange coloured flesh and a poisonous seed which is smooth and elliptic. The seed has an open system of fibrous veins on the yellowish surface.^[7][8]

Karaka's wood anatomy prevents them from being dated using the conventional technique of counting annual growth rings in the trunk. Karaka trees planted in Palmerston North in 1962 grew to a height of 14 m (46 ft) in 42 years. The largest stem diameter measured 26.5 cm (10.4 in), and the trees grew 0.68 mm (0.027 in) per year. Other karaka trees grew at different rates; the largest karaka tree on mainland New Zealand which was 500 years old with a diameter at breast height (DBH) of 212 cm (83 in) and a growth rate of 0.43 cm (0.17 in) per year.^[6]

The fruit ripens between January and April and the seeds are mostly dispersed by two columbiform birds, the kererū and the parea, which also feeds on its fruit. In modern-day New Zealand, the majority of karaka seeds germinate within 8 m (26 ft) of a parent tree, indicating that the tree does not normally spread out very far.^[9][3]

• 
  Close-up of karaka's greenish-yellow flower panicle and characteristic leathery, oval-shaped leaves
• 
  Clusters of karaka fruit showing different ripening stages, from green to orange-yellow, hanging from branches with yellowing leaves
• 
  Dense foliage of a mature karaka tree showing its characteristic branching pattern and dark green, glossy leaves

Karaka (Corynocarpus laevigatus) was first described by the German naturalists Johann Reinhold Forster and Georg Forster in 1776, though their description was incomplete, and the figures of the parts of the flower were inaccurate. It was described from specimens collected on the second voyage of James Cook. Sir Joseph Banks and Daniel Solander, who were the botanists on the first voyage of James Cook, also brought specimens of C. laevigatus to England, where they described and figured it under the name Merretia lucida, though their work was never published.^[10]

Karaka (Corynocarpus laevigatus) is a unique medium-sized tree endemic to New Zealand, unlikely to be mistaken for any other native, foreign, or naturalised tree. It can be readily identified by its orange drupes and its leathery, dark green leaves.^[11] Karaka is in the family Corynocarpaceae, which includes four other species in the genus: (C. similis) in Vanuatu, (C. cribbianus) in the Solomon Islands, North Eastern Queensland and Vanuatu; (C. dissimilis) in New Caledonia; and (C. rupestris) in the Australian states of New South Wales and Queensland.^[6]

Corynocarpaceae may have originated from a Paleotropical centre, then two separate radiations into colder climates. In the first, C. cribbianus and C. rupestris were found in Australia through New Guinea, while in the second, C. dissimilis, C. similis, and C. laevigatus were found in New Caledonia, which led to New Zealand. Fossilised Corynocarpus kernels from the early Miocene era were found at Landslip Hill in the Southland Region, indicating that the genus has a long history in New Zealand. It is possible that Corynocarpus spread from New Caledonia to New Zealand via land connections that existed in the mid-Tertiary era.^[12]

The etymology of Corynocarpus translates to English to "club fruit", and the Latin specific epithet laevigatus translates to "smooth", in reference either to the fruit of the leaf or the skin. In the Māori language, karaka can either refer to the fruit of the tree or the tree itself. Karaka is also the Māori word for the colour orange.^[13][7] In the Moriori language and on the Chatham Islands, the tree is known as kōpi. The tree is also known in English as the New Zealand laurel.^[14]

Karaka is in large numbers throughout the North Island and South Island as far south as the Banks Peninsula on the east coast of the South Island and Greymouth (on the West Coast).^[4][5] Karaka is also found on the Chatham Islands, Kermadec Islands, and the Three Kings Islands.^[12] Sources generally agree that before Polynesian arrival in New Zealand, karaka was likely limited to the northern North Island, despite its current range across offshore islands and the northern South Island.^[15] In the far north of New Zealand, where kauri (Agathis australis) forests are its natural vegetation type, the density of karaka is low (2.5 stems per hectare). Populations can be significantly denser further south, where karaka has spread from Māori plantings. A 2006 study by the New Zealand Journal of Botany indicated an average canopy coverage across plots in karaka stands was 41%, with a maximum cover of 75%. Its estimated altitudinal range is between 29°N and 38°S.^[6] If planted, karaka can survive as far south as Dunedin.^[16]

It is naturalised and considered an invasive species in Hawaii, where it is naturalised in moist soils and considered a threat to endangering rare plants such as Exocarpos luteolus.^[17][18] Karaka is also grown in Southern California.^[19][20] Karaka was introduced to Hawaii for reforestation purposes and was first naturalised to Kauai in 1891, and is still commonly found throughout the island.^[19][18] Karaka is primarily naturalised on the island of Kauai. It is also found on the islands of Hawaii, Molokai, and Oahu.^[21]

Karaka is a valuable food source for New Zealand birds.^[22] The kererū (Hemiphaga novaeseelandiae) and the Chatham Islands pigeon or parea (Hemiphaga chathamensis) are the only are the only extant bird species with a gape large enough to consume the fruits of karaka.^[23] The extinct moa and other large birds likely consumed karaka fruits centuries ago.^[24]

A 1966 article from the Ornithological Society of New Zealand reported a New Zealand bellbird (Anthornis melanura) feeding on the sap from the bark of the karaka.^[6] Other smaller New Zealand birds such as the North Island robin (Petroica longipes), silvereye (Zosterops lateralis) and whiteheads (Mohoua albicilla) are known to search around karaka trees for insects.^[25] The endocarp of karaka is usually nibbled by Polynesian rat (Rattus exulans), while the larger brown rats (Rattus norvegicus) occasionally chew open the endocarps. Both species consume the flesh of karaka.^[6] Possums (an invasive species in New Zealand) are also known to consume the ripe flesh of karaka berries.^[26]

Karaka is common in cultivation and widely available for sale both in New Zealand and elsewhere in the world.^[1] It was one of the most grown food crops by pre-European Māori (alongside kūmara and aruhe); they ate the drupe and seed after a long detoxification process.^[27][28] Karaka berries contain a highly toxic alkaloid called karakin.^[29] Initial symptoms of poisoning include diarrhoea, nausea and restlessness which develop to more severe gastrointestinal and neurological problems.^[30]

Every autumn, pre-colonisation Māori would collect the seeds dropped from the coastal karaka trees. The seeds would be placed in open-weave traditional baskets (kete), washed in water to remove the outer pulp and baked and sun dried, a process that would remove toxicity from the seeds.^[31][32]

Karaka is of great importance to Māori, who primarily used it as a food source.^[33][34] In Māori mythology, karaka is told to be from Hawaiki, an ancestral homeland for the Māori people.^[16][35] While pre-European Māori primarily valued karaka for nutrition rather than medicine, they did use leaf undersides to draw out infections and fresh upper surfaces to heal injured skin.^[36] The seeds of karaka were of great value to Māori and needed to be prepared before they could be safely consumed, while the flesh of the berry was consumed uncooked. The seeds are very poisonous and bitter in taste which had to be steamed properly in earth ovens (umu).^[4][37] Karaka wood is used in constructing canoes (waka).^[38]

On the Chatham Islands, karaka has played a distinguished role in the history of Moriori people; the bark of these trees has been used for making dendroglyphs. A 2000 Department of Conservation report documented 147 karaka trees with dendroglyphs on the Chatham Islands, though not all carvings were confirmed as authentically Moriori.^[39][40] Karaka (or kōpi in Moriori) is considered a taonga (cultural treasure) amongst the Māori and Moriori peoples. Carvings on karaka trees, known as rākau momori in the Moriori language, typically depict Moriori ancestors and are considered internationally significant and unique to their culture. A rāhui protects the remaining carved trees due to their fragile state, with conservation measures underway. Karaka wood was also utilised by the Moriori to smoke and preserve food.^[41][42]

An exoplanet originally named HD 137388 was renamed to "Karaka" in 2019 in honour of the tree's orange fruit.^[43] A small community 20 km (12 mi) west of Whanganui named Pākaraka is also named in honour of the tree and its name reflects the "abundance of karaka trees" that previously were situated here.^[44] New Zealand Post recognised karaka in 1967 by featuring it on penny postage stamps.^[45]

• List of trees native to New Zealand

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• Media related to Corynocarpus laevigatus at Wikimedia Commons