Corynocarpus laevigatus

Corynocarpus laevigatus, commonly known as karaka or the New Zealand laurel, 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. C. laevigatus individuals are also found on the Chatham Islands, Kermadec Islands, and the Three Kings Islands. C. laevigatus is mostly a coastal tree, although in the North Island, it is also found inland.

Corynocarpus laevigatus was first described in 1776 by the German naturalists Georg and Johann Reinhold Forster. C. laevigatus grows to heights of up to 15–20 metres (49–66 feet) and has a stout trunk of up to 60 centimetres (24 inches) in diameter. Its leaves are leathery, dark to bright green in colour and up to 15–30 cm (6–12 in) long. From August to November, C. laevigatus produces large oval-shaped orange-coloured fruits, about 30–40 mm (1.2–1.6 in) in length. C. laevigatus seeds are highly toxic to humans and contain poisonous toxins and other glucosides of 3-nitropropionic acid. The fruits are a valuable food source for the kererū (Hemiphaga novaeseelandiae) and the Chatham Islands pigeon (Hemiphaga chathamensis). C. laevigatus has been introduced to the United States for reforestation purposes; it is naturalised and considered an invasive species on several Hawaiian islands and is mostly found on the island of Kauai.

It is considered a taonga (cultural treasure) amongst the Māori and Moriori peoples, who valued C. laevigatus for its drupes and seeds. On the Chatham Islands, depictions of Moriori ancestors were carved on to C. laevigatus trees (known as rākau momori) and 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.

Corynocarpus laevigatus (karaka) is a medium-sized evergreen leafy canopy tree with erect spreading branches. It is endemic to New Zealand. It grows to heights of up to 15–20 metres (49–66 feet) and has a stout trunk usually up to 60 centimetres (24 inches) in diameter, but can be up to 1 metre (3 feet 3 inches) in diameter. The largest trunk of a C. laevigatus specimen diameter ever measured was 3 m (10 ft) in diameter. Its bark is typically a grey colour, although on young trees it can is a lighter brown-colour. C. laevigatus is predominantly a coastal tree, although in the North Island, it can also be found in lowland inland forests. C. laevigatus is suggested to have a maximum lifespan of 500 years in mainland New Zealand, and potentially 600 years from a solitary specimen examined on Lady Alice Island.

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. C. laevigatus'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. C. laevigatus 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.

From August to November, C. laevigatus 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 and November, and each panicle may have up to 100–200 flowers. Its sepals are rounded, and its petals are vaguely spathulate (spoon-shaped). Each panicle on an inflorescence (flower cluster) can be up to 200 mm long. The fruit C. laevigatus produces are 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. The fruit has a sickly sweet taste, reminiscent of apricots or dates. Its leaves are dark green in colour, paler green beneath, thick, leathery, and are vaguely obovate (egg-shaped) to oblong (rectangular) in character.

Corynocarpus laevigatus's wood anatomy prevents them from being dated using the conventional technique of counting annual growth rings in the trunk. C. laevigatus specimens 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 C. laevigatus trees grew at different rates; the largest C. laevigatus tree in mainland New Zealand 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. The fruits of C. laevigatus usually ripen between January and April and the seeds are mostly dispersed by two native columbiform birds, the kererū and the parea, which also feeds on its fruit. In modern-day New Zealand, the majority of C. laevigatus seeds germinate within 8 m (26 ft) of a parent tree, indicating that the tree does not normally spread out far. C. laevigatus has a diploid chromosome count of 46.

At least 11 compounds have been identified in C. laevigatus. A unique nitropropanoyl glucopyranose called 1,4,6-tri-(3-nitropropanoyl)-β-D-glucopyranose (corynocarpin) was first identified and extracted by a 1978 study published in Phytochemistry. A 2025 study examined the phytochemical screening of C. laevigatus extracts and revealed that the tree contains "significant amounts of phytochemicals".